Running .035" Squish In 8V Cylinder Head

[glhs613]

Does anyone have any experience with running a "Tight" 0.035-0.040" squish clearance in the 8V Chrysler turbo motors? In specific, I'm curious how much additional static compression ratio might be possible with the 0.035" squish versus the standard 0.075-0.090" clearance? (Or whatever is typical) I've seen more and more articles where n/a engine builders were able to gain a few tenths of a compression point with setting a 0.035 squish. The tight squish clearance supposedly promotes better turbulence in the combustion chamber and gives some additional detonation resistance. My question is, how much additional detonation resistance in a 8V turbo motor? Would it be enough to go up 0.5 on static compression ratio?

[turbovanman²]

Subscribed.

[glhs875]

I think that is something well worth pursuing!

[5DIGITS]

..."Tight" 0.035-0.040" squish clearance in the 8V Chrysler turbo motors?

Excellent topic.
The benefits of doing this (decking the block approx. .040") can be well worth it.
Keep in mind that the engine to engine variations should have you measuring and determining how much needs to be cut, for YOUR engine.
I personally do not focus on the compression gain as much as I concentrate on squish and knock suppression.
The 2.2 has older attributes and the compression/ring-land locations are two key items that are 'Yester-tech'!!
Therefore, decking the block (not milling the head) and adding squish to a currently 'dead' chamber will breathe new life into the engine while the added squish will suppress knock.

When trying to do this, remember that the shape and depth of the piston dish can be a complimentary tool to the chamber.
In short, when the piston dish diameter and depth is well matched with a modified chamber, squish can be optimized to a relatively high level and aggressive timing without knock is the benefit.
Although, if you utilize a standard piston, the benefits are still there !!
A good point of reference - The spark advance that required a racing fuel mix should now be available with pump gas.
That can be approx. 5-7 degrees of spark advance improvement and even higher if its an optimal arrangement.
Add the race gas back into the equation with additional spark and the true benefits can now be realized.

Note: depending on how much needs to be removed from the deck on your engine, you may require a shorter cam belt.

I hope this helped.

[4 l-bodies]

Or, if you are ordering custom forged pistons you can alter the CH height bringing pistons past TDC and out of the hole. No issues with timing belt being too long this way, or cam timing being substancially retarded. However this can give you other issues like valve relief depth if running bigger camshaft lift, and increased compression ratio. I typically run all my 8v pistons about .015 out of the hole and it likes it. That puts me about .050 squish running Cometic gasket. That is about .025-.027 higher than factory.
I personally think the factory turbo piston design and being at least .010-.012 down the hole to begin with, makes for far less than optimal squish/quench. Seems like lots of area for impovement.
Todd

[4 l-bodies]

I think that is something well worth pursuing!
Some of us have been for many years (lol).

[88C/S]

Or, if you are ordering custom forged pistons you can alter the CH height bringing pistons past TDC and out of the hole. No issues with timing belt being too long this way, or cam timing being substancially retarded. However this can give you other issues like valve relief depth if running bigger camshaft lift, and increased compression ratio. I typically run all my 8v pistons about .015 out of the hole and it likes it. That puts me about .050 squish running Cometic gasket. That is about .025-.027 higher than factory.
I personally think the factory turbo piston design and being at least .010-.012 down the hole to begin with, makes for far less than optimal squish/quench. Seems like lots of area for impovement.
Todd

So that would require increasing the valve relief depth(.025 -.027) by the same amount?

[glhs613]

Todd/5DIGITS,

Thanks for the response. Per Todd's comment "factory turbo piston design and being at least .010-.012 down the hole to begin with." That is pretty much exactly what I measured on my 2.2L 8V buildup. With that said, Cometic makes custom head gaskets of various thicknesses and they show one in their catalog at 0.035." I CC'd my cyl head and piston bowl so I know where I am from that standpoint. I think I can achieve the "Tight Squish" I'm looking for with the thinner gasket but I will have to machine material out of the piston bowl or combustion chamber to get the proper C.R. I'm looking into which of those options right now but I was hoping to get some feedback on where to set my C.R. Stock is 8.2:1. With the .035" squish I'm comfortable bumping up a few tenths while still running 92 octane pump gas. I just don't know if I should venture above 8.5:1. Your thoughts?

My hard-parts list:
-Forward Motion S3 Cyl head - Early Non-CNC version with 53cc chambers
-FWD-Perf S3 Cam
-Wiseco Forged Pistons
-Garrett GT3076 DBB Turbo
-BIG Air-to-air IC
-Tunable Fuel/Ignition

Thanks,

Steve Coghill

[4 l-bodies]

Todd/5DIGITS,

Thanks for the response. Per Todd's comment "factory turbo piston design and being at least .010-.012 down the hole to begin with." That is pretty much exactly what I measured on my 2.2L 8V buildup. With that said, Cometic makes custom head gaskets of various thicknesses and they show one in their catalog at 0.035." I CC'd my cyl head and piston bowl so I know where I am from that standpoint. I think I can achieve the "Tight Squish" I'm looking for with the thinner gasket but I will have to machine material out of the piston bowl or combustion chamber to get the proper C.R. I'm looking into which of those options right now but I was hoping to get some feedback on where to set my C.R. Stock is 8.2:1. With the .035" squish I'm comfortable bumping up a few tenths while still running 92 octane pump gas. I just don't know if I should venture above 8.5:1. Your thoughts?

My hard-parts list:
-Forward Motion S3 Cyl head - Early Non-CNC version with 53cc chambers
-FWD-Perf S3 Cam
-Wiseco Forged Pistons
-Garrett GT3076 DBB Turbo
-BIG Air-to-air IC
-Tunable Fuel/Ignition

Thanks,
Steve Coghill

Steve,
If running Cometic gasket make sure RA finish is fine on deck and head. Obviously you should not assume deck is flat to begin with. It needs to be if using Cometic gasket as they do not compress much (if any). If your using swirl head, you might gain a couple more cc's by unshrouding valves further. With your ability to tune ignition and fuel, you should be able to run a bit more compression than the factory. That is of course dependent on available fuel, amount of boost, and environment your in. I've personally heard of many guys running standalone EFI running 8.5 or even a bit more on pump fuel.
Todd

[GLHS60]

This is a great topic. I have always considered .035 to be ideal squish but have been reading that in some cases highly boosted engines can actually benefit from reduced squish. As in approx. .110 clearance. Any one have any input??

Thanks
Randy

[4 l-bodies]

This is a great topic. I have always considered .035 to be ideal squish but have been reading that in some cases highly boosted engines can actually benefit from reduced squish. As in approx. .110 clearance. Any one have any input??

Thanks
Randy
Not saying I'm in this camp as I try to tighten up squish in my 8V applications, but there are people out there that think squish/quench is not particularly important in forced induction applications. I've been debating this with my Cosworth motor for a while now. The factory Mahle forged pistons have a ridicuously large 49cc dish piston. That makes for a far heavier piston than it needs to be. Also the flame propagation or travel can't be ideal with a piston design like that. Anyway, a couple guys had some Cosworth pistons made by Ross a few short years ago. They sent sample Mahle Cosworth pistons to them, and Ross determined their design would use a flat top piston. They were very light and they just ran the piston WAY down the hole. Another forum member bought a disassembled 2.0 Cosworth motor from a Bonneville salt flat racer. He used Aries pistons. They also came back designed as flat tops as well, They were designed for a forced induction application. Like the Ross, just ran it down the hole like .250! Obviously with no regard to any squish whatsoever. The Cosworth is an extreme example as their chambers are only around 29cc (compared to 50-56cc for the 8V heads). To run pistons up near TDC required a HUGE dish piston if using in a forced induction appication. All the pics I've seen of the the Hans Herman head pistons that went into #001 appear to be flattops as well. I don't think the chamber had nearly big enough cc to do this without running the piston quite far down the hole like the Cosworth. Obviously using the same "screw the squish" approach.
Todd

[5DIGITS]

... but there are people out there that think squish/quench is not particularly important in forced induction applications.
A good example of benefits and need for squish is the effort put into the SRT Turbo 2.4.
The engine was originally developed by Rousch for the Mexican Stratus turbo but it was lethargic in many respects.
A key piece to improving the output of the engine while reducing knock sensitivity was the 'ski ramp' piston tops.
16V chambers do not offer much shrouding when compared to the 2V chamber, therefore the piston top is modified to bring it out of the hole and closely mate with the chamber.
This supported a 7 degree spark advance increase across the board and 10-11 degrees in specific areas and therefore a significant gain in torque and HP, over the original piston.
Although, there is an obvious down side to adding height to the piston - weight! This added piston weight, above the wrist pin, can induce added wear on piston skirts due to the pistons tendancy to 'bobble' in the bore, between combustion events. Therefore, the added weight obviously needs to be concentric and/or well balanced with respect to the wrist pin axis. In short, in cases where decking the block will not provide all of whats needed, it's a justifiable trade-off when done properly.

[glhs875]

I have been involved with the tuning of the 2.4 engine using flat top pistons which decreased the quench. The combo was VERY sensitive to ignition timing and was unable to run much timing advance without running into detonation. Although it still made alot of power.

[Vigo]

I was moved to give this thread 5 stars.. and i dont think ive ever rated a thread before! Good info in here!

[GLHS60]

To expand the discussion even further some feel squish and quench are not exactly the same thing.
Please discuss.

Thanks
Randy

[GLHS60]

Making higher power with less advance is not a bad thing.

Thanks
Randy


I have been involved with the tuning of the 2.4 engine using flat top pistons which decreased the quench. The combo was VERY sensitive to ignition timing and was unable to run much timing advance without running into detonation. Although it still made alot of power.

[glhs875]

I don't disagree with your statement. It would of been interesting to see how the combo would have performed with more quench being the only change!

[zin]

To expand the discussion even further some feel squish and quench are not exactly the same thing.
Please discuss.

Thanks
Randy

Technically, they aren't, kind of like pre-ignition and detonation, similar, but not quite the same...

Quench is what happens to the flame front when it gets to withing a few thousands of something, like the cylinder wall, chamber, etc. In effect, the cooler (compared to the flame) piece quenches/extinguishes the flame front. This can be beneficial if the part you are quenching is the volatile "end gasses" that are prone to detonation. Not so good for emissions as those same surface areas will have a bit of unburnt hydrocarbons that will exit with the exhaust, driving up emissions, or at least adding to the burden of the catalytic converter.

Squish is what happens when you bring two movable surfaces together, in this case the piston and the chamber. You can imagine what is happening to the mixture when this occurs, they are "squished" out into the open part of the chamber, the resulting turbulence is great for combustion efficiency.

It is even better if the part you're "squishing out" is the end-gasses (the last part of the mixture to burn), as they are what is going to "detonate" due to their exposure to the highest heat for the longest time.

One of the reasons these two things get confused, is that you rarely have one without the other, though I suppose you could have squish without quench if the two surfaces don't get that close to each other.

In order to use quench as an advantage, you'd want it to be where the end-gasses will be. The idea is to use the two surfaces to "blow" the remaining mix into the oncoming flame front, while snuffing out/quenching the part of the chamber/mixture that is most prone to detonation.

Sounds complicated but it really isn't. Basically you'd like to have a chamber and piston that come close to each other, .035 is a good place to start, much wider and you loose much of the effect, tighter and you're likely to have things "talking to each other".

Aside from welding up the chamber, I don't see much that can be done to make things much better besides running the piston higher/decking the block to get the .035" clearance, but perhaps 5DIDGITS has some insight he'd care to share?...

Mike

PS I agree with you in regards to making max HP with min timing, that's what we should be shooting for, and these mods will help in that area, as well as making the engine more tolerant to fuel quality, ie more boost on lower octane.

[GLHS60]

I'm a one finger typer so I have to simplify things.

Squish - squeeze

Quench - cool

Detonation - after plug fires

Pre-ignition - independant of plug firing

Thanks
Randy

[GLHS60]

Yes, I'm with you there. While there is no doubt squish is important N/A, the question is, at what boost level and circumstances might it become a negative. It seems there might be a point when there can be too much turbulence.

Thanks
Randy




I don't disagree with your statement. It would of been interesting to see how the combo would have performed with more quench being the only change!

[Reaper1]

This topic has been on my mind for a LONG time (ever since I was on the Endyn TOO forum). After looking at the chamber and the piston, I came up with a piston design that allowed good, tight squish where needed, directed the charge toward the exhaust valve, and still kept a reasonable static compression ratio. Although, if done very well, the static compression ratio isn't really that important.

Basically instead of the piston having a symmetrical deep dish, the dish was a ramp shape (deeper side on the exhaust side of the chamber) and the edges closely followed the contour of the chamber. Obviously this would have to be a custom piston, but it is possible to do. Depending on cam choice and how close the dish ends up being to the valves, this design might need valve reliefs and most certainly would become an interference engine. This was all based on information from Larry Widmer both from the forum and from his archived articles. The only thing different is that the dish on my proposed pistons wouldn't be as tight on the intake side so as to reduce the static compression ratio a bit since we are going to be artificially making the density of the charge higher than it normally would be. This is used by Larry on pistons that are designed for FI applications. This is a VERY good read and I think it should be mandatory for anyone looking to explore this type of design: http://www.theoldone.com/articles/The_Soft_Head_1999/

Todd, by "Cosworth" engine, you are talking about the Masi 16V engine, correct (because the head was cast by Cosworth)? If/when I ever need to build a new bottom end for my engine, I am going to employ the strategies of the "Soft Head" design. I believe 100% that the Masi head would be even more incredible if the entire system was used. As a note: the Venolia pistons that are in my Masi engine do mimic the stock piston design, but with a more shallow dish which gives a static compression ratio of 8.5:1 IIRC (could be 8.2). The area outside the dish are at the top of the bore and match the head's chamber shape to provide squish.

Warren Stramer is running his pistons down in the hole by a bit (similar to the NSRT 2.4 Turbo) and when asked about it he responded that he has noticed a current trend for high performance FI engines to not be using squish much, if at all. While I can't argue with his results, knowledge, or skills, I can't agree with that thinking simply because it doesn't make much sense if you look at the "problem" from an engineering physics point of view. Maybe I'm all "starry eyed", and have fallen prey to an elaborate gimmick, but I've seen the results from using this train of thought in practice, and I've had other very experienced engine people agree with it as they'd also messed with portions of the idea and seen results themselves. Also, given that new, high efficiency engines are employing this type of design (which Larry and his company have been contracted by auto makers to develop products for them)...I can't help but to believe this is the way to go.

[Ondonti]

The engineering point of view is only valid when all variables have been accounted for and deciding that all things are accounted for ends up being a subjective call. So, in the end, it is something to think about but very expensive or problematic to refine into a perfect answer without doing hands on testing. Those F1 teams spend millions on the hands on testing because they know they can't figure out all the variables sometimes and testing either reminds us of things we have forgotten or teaches us things we were not aware of.

When you bog down on the thinking side of things its time to test what you have come up with and find out what you are missing.

[GLHS60]

While there is no doubt squish is important N/A, the question is, at what boost level and circumstances might it become a negative. It seems there might be a point when there can be too much turbulence.

Thanks
Randy

[johnl]

Complex shapes, be they of chamber or piston, all increase surface area and that reduces combustion efficiency yet those complex shapes are created for good reasons. A jumble of compromises. Good thread.

[GLHS60]

Great thread for sure. I am a firm believer in proper squish but what got me thinking was a few years ago I bought some flat top 2.5 Venolias and was planning on doing a custom dish. A friend who also bought a set just machined the tops off to achieve approx. 8:to1 so his pistons were way down the hole and his engine ran really strong with no detonation problems. Anecdotal evidence for sure but not a detonation monster like I expected. I continued reading and came across the idea that there could be too much squish induced turbulence under high boost situations. Emphasis on high boost!!

Thanks
Randy

[Vigo]

It would be nice to know how to judge that so i could decide whether to try to use a tighter 'squish' on any upcoming engine assemblies.

[zin]

While I'm a firm believer in the "weird sh!t happens" philosophy, I don't think I can quite get on board with the idea that boost would affect whether or not squish/quench is effective. Boost basically effects the density of the charge, but not so much its action, add to that the fact that there is typically back pressure on the order of 50% or more of the boost charge, and this becomes even more unlikely in my eyes.

Even supercharged engines, which aren't burdened with the relatively high back pressures, don't seem to follow the idea that quench/squish loose their effectiveness at any boost pressure.

The only thing that comes to mind that might make this partially true is if they are referring to such high boost that no amount of squish/quench will stave off detonation, but that's hardly the "fault" of squish/quench...

It is conceivable to me that, say in the case of F1 engines, other considerations could take precedence. I can imagine that the design of the ports and/or the chambers don't benefit enough from added quench or squish as much as they might from say lower surface to volume ratios or even just added volume (space to put mixture).

Like almost all things in life, I'm sure there are exceptions, which is probably where this notion came from, and so I'll reserve final judgment as I certainly haven't looked for the exceptions, and welcome further knowledge, I'm firm in my knowledge, but open minded enough to entertain other possibilities, if the facts support them.

Seems we are of similar mindset here.

Mike

PS Vigo, running tighter than is needed to provide quench won't yield better results, but will increase the possibilities of interference, so I wouldn't go that way unless there was some other compelling reason to do so.

[Force Fed Mopar]

Bore size may come into play also.

[Vigo]

It is conceivable to me that, say in the case of F1 engines, other considerations could take precedence.

Bore size may come into play also.

I think F1 engines are a completely different ballgame because of the RPM. I think there is a point where you start 'outrunning' detonation with rpm. I also think a small bore size makes detonation easier to control, and a lot of f1 engines throughout history have had smallish bore sizes although the last few years they were allowed up to 98mm.

[Reaper1]

Also keep in mind those F1 cars are running methanol from what I remember.

Brent, you are correct that at some point you gotta make the thing and try it! Math, physics, computer models...they can only get you so far. Real life is the true test.

I think the one thing to keep in mind is that this idea works as part of a system. I don't think that having super small squish areas just by itself will do much good. You have to have a swirl inducing chamber and you have to be able to place the charge where you want it in the chamber.

I also do not buy into high boost affecting how squish works. We are dealing with a compressible gas that hopefully has stratafied fluid in it. It doesn't matter what density it is, as long as it is still compressible. Now, you CAN cause issues if there are places in the chamber that are dead and cause the fluid to fall out of suspension. This is why I don't believe there is such thing as too much turbulence in the chamber. I've heard of some people worrying about centerfuging the fluid out of suspension, but again, that's what turbulence is for.

No matter the chamber design, amount of squish, ect. you are always working with a fuel that has limits. Yes, a well designed chamber will allow you to take full advantage of those limits, but they are still there. If you push past them, you will still experience the detonation issue. Squish, swirl, turbulence....they are not cures for detonation, they are tools to be able to take full advantage of the fuel's resistance to it.

I think the most important thing to remember is that not one of these things singly will make a huge difference. They are all part of a system. If something is missing, the system will either not work as well as it could, or not work at all and possibly worse than if that part wasn't there at all.

[Shadow]

Great thread for sure. I am a firm believer in proper squish but what got me thinking was a few years ago I bought some flat top 2.5 Venolias and was planning on doing a custom dish. A friend who also bought a set just machined the tops off to achieve approx. 8:to1 so his pistons were way down the hole and his engine ran really strong with no detonation problems. Anecdotal evidence for sure but not a detonation monster like I expected. I continued reading and came across the idea that there could be too much squish induced turbulence under high boost situations. Emphasis on high boost!!

Thanks
Randy

I'm Diggin the new sig pic!!!! :)

[GLHS60]

I'm Diggin the new sig pic!!!! :)

Thanks man !!!

Thanks
Randy

[Shadow]

Making higher power with less advance is not a bad thing.

Thanks
Randy

This ^^




Brent, you are correct that at some point you gotta make the thing and try it! Math, physics, computer models...they can only get you so far. Real life is the true test.

This ^^




I think the most important thing to remember is that not one of these things singly will make a huge difference. They are all part of a system. If something is missing, the system will either not work as well as it could, or not work at all and possibly worse than if that part wasn't there at all.

And This ^^

rob out ;)

[turbovanman²]

Hmmm, gonna have my TIII apart soon, hmmmmmmmmm.

[BadFastGTC]

A good friend of mine told me something a number of years ago that was also quoted by John Kaase in so many words after another win in the Engine Masters Challenge. The piston dish should mirror the combustion chamber. I have seen some very tight quench gaps. Personally, from what I have researched on it, we cannot go wrong with improvements in it. But as Kaase stated, most people are not willing to go through the effort and expense to do it.

[GLHNSLHT2]

Indy/CART cars used to use methanol. F1 uses highly advanced gasoline though.

[Force Fed Mopar]

A good friend of mine told me something a number of years ago that was also quoted by John Kaase in so many words after another win in the Engine Masters Challenge. The piston dish should mirror the combustion chamber. I have seen some very tight quench gaps. Personally, from what I have researched on it, we cannot go wrong with improvements in it. But as Kaase stated, most people are not willing to go through the effort and expense to do it.

So basically the ideal thing would be to have everything else done in the cyl/chamber, take all the measurements possible, then take a mold of the combustion chamber and send it to the piston manufacturer and have them make it to match w/ the specs you want. And to really optimize it, you would have them design the piston to be as light and balanced as possible, then have rods made to match.

[turbovanman²]

A good friend of mine told me something a number of years ago that was also quoted by John Kaase in so many words after another win in the Engine Masters Challenge. The piston dish should mirror the combustion chamber. I have seen some very tight quench gaps. Personally, from what I have researched on it, we cannot go wrong with improvements in it. But as Kaase stated, most people are not willing to go through the effort and expense to do it.

I remember that. I get the Engine Masters magazine once in awhile and remember he mentioned that with one of his builds.

[Vigo]

The idea of mirroring the combustion chamber in the piston kind of seems like an oversimplification that could land you with a needlessly intricate piston design. Seems to me like the main thing that 'shape' of the combustion area can do to combat detonation (not really talking about squish or designing out hot spots etc) is to make the distance that the flame front must travel from the ignition point uniform in all directions as much as possible while working around the many many constraints, like the valve locations and the fact that the ignition point is not usually the center of the combustion space. If im wrong id like it to be pointed out and explained to me.. :)

[zin]

I'll disagree with that, not that it isn't a good thing, as it does help combustion efficiency, but doesn't guarantee any benefit against detonation.

That said, improving efficiency would reduce some tendencies to detonate, but without other elements, such as quench, may not be worth the effort, especially when you're talking about moving the position of the sparkplug, not easy! The main benefit would be to limit the residence time of the mixture in the most unstable portion of the chamber, but often lighting that portion would be more beneficial than a central location.

If you burn the nitroglycerin first, the C4 might go off, but if you burn the C4 first, the nitroglycerin WILL detonate on its own, far ahead of the flame front, simply due to the rising heat and pressure.

Mike

[Vigo]

Well if you assume that heat and pressure 'travel' faster than the flame front, then distance has to be some kind of factor. If you put the spark plug all the way to one side of the cylinder, wouldnt that make the engine more likely to detonate at the other end of that cylinder?

[OmniLuvr]

The idea of mirroring the combustion chamber in the piston kind of seems like an oversimplification

yes, but to a point, it really prob depends on the shape of the combustion chamber, id like a g-head piston that matched the combustion chamber, not just the small circle dish they came with.

and so far im liking how my t3 flat tops are performing with my g-head (they had about .013 pop out when installed?) and failpro headgasket @ 20 psi, just need a little more ball$ to use premium fuel instead of e-85 and see where it takes me...

[zin]

The heat generated by the increasing pressure of combustion does effect the charge/chamber as a whole, and all at once, so the flame front isn't as dominate as one tends to expect. This is why a hot spot (plug tip, exhaust valve, etc) can be both a point of pre-ignition and detonation. Both tend to make the "local" mixture less stable, one before ignition and the associated pressure rise, one just by itself, both with similar outcomes.

Since detonation is the uncontrolled combustion of the end gasses, which by definition are at the "end" of the combustion chamber, you'd be correct that distance can make a difference, both in terms of detonation (as in how long will the "far end" be subjected to rising temps/pressures), and whether or not the hot/unstable portion is consumed before it can "go off".

An example would be the ubiquitous SBC angled plug head. While both the straight and angled plug heads have the plug in roughly the center of the chamber, the angled plug reduced detonation dramatically buy angling the plug towards the hot exhaust valve area, thereby burning the hottest/most unstable portion of the charge first, leaving the portion that could best endure the heat and pressure as they increase.

You'd also be correct in that the mirroring of the chamber in the piston is an over-simplification. If one knew of nothing else to do, mirroring would have a good chance at "fixing" a detonation problem and/or increasing combustion efficiency, but would likely be less than optimal, though the "shot gun" approach might hit some of the targets.

Mike

[glhs875]

yes, but to a point, it really prob depends on the shape of the combustion chamber, id like a g-head piston that matched the combustion chamber, not just the small circle dish they came with.

and so far im liking how my t3 flat tops are performing with my g-head (they had about .013 pop out when installed?) and failpro headgasket @ 20 psi, just need a little more ball$ to use premium fuel instead of e-85 and see where it takes me...


I have a set of those T3 pistons that I plan on using on an 8v engine as well! But I will be using a Cometic headgasket.

[zin]

yes, but to a point, it really prob depends on the shape of the combustion chamber, id like a g-head piston that matched the combustion chamber, not just the small circle dish they came with.

That arrangement would actually be pretty good! It's close to a fully spherical chamber, which has excellent surface to volume ratio and would effectively force the out laying gases into the combustion space, aiding turbulence.

A couple of downsides, off the top of my head, would be that the hottest part of the mix wouldn't be lit first, due to the plug placement, though I'm not sure just how much that would effect things...

Second would be that timing could be tricky. If started too soon, it could "set off" the mix before it gets quenched by the piston and chamber. This has more to do with quench than squish, kind of like snuffing out the fuse on the dynamite before it gets to the stick.

This also assumes a reasonable compression ratio could be obtained between the piston and chamber without ridiculously shaped/configured pistons.

Mike

[Reaper1]

Most well designed 2-valve combustion chambers (with the few exceptions) will typically aim the spark plug toward the exhaust valve. This is done for the exact reasons Mike pointed out.

Now, lets think about the chamber design as a whole (which includes the piston face). If you simply mirror the upper part of the chamber in the head onto the piston, yes, you will get more squish, more quench, and probably better combustion efficiency as a whole. BUT, the charge is still over most of the face of the piston, which means a good portion of it isn't near where the combustion event starts at all. This is where we start to NOT mirror the upper part of the chamber. You want to actually force the charge into the area where the plug is, and bias it towards the exhaust valve.

Now, the reasons for doing that don't just lie in the combustion event. Think about what happens AFTER the charge is spent. Now we have the exhaust stroke in a 4-stroke engine. By not only mirroring the upper part of the chamber, but also biasing the volume towards the exhaust valve, now we are forcing the spent charge out of the open exhaust valve and making sure the chamber is as purged as it can be of the spent charge. THAT is the part of the trick they aren't telling you!

Now, add in a tiny bit of valve overlap along with swirl and you can really clean the chamber out for the next cycle!

[glhs875]

(Now, add in a tiny bit of valve overlap along with swirl and you can really clean the chamber out for the next cycle![/QUOTE])



A little overlap can help to cool the exhaust valve during that cycle as well. I like the idea of using a piston/chamber design to force things where they need to go. This is a good thread!

[OmniLuvr]

i feel as if the swirl pistons with a g-head doesnt have a good quench area (because the dish is so large), but they seam to work good, not sure if its the low comp ratio or?

i ran a swirl head on g-head pistons and e85 with no intercooler (14.7psi) and made enough power to blow up the stock 525, which isnt saying much i guess? but it still felt pretty good, i wanted to take it farther, but went with the g-head/t3 piston motor while swapping in a 523 instead.

i think i might even try the swirl head on the t3 piston motor next, prob a little easier to get a tune for it i think... just worried about valve to piston issues...

[johnl]

A good friend of mine told me something a number of years ago that was also quoted by John Kaase in so many words after another win in the Engine Masters Challenge. The piston dish should mirror the combustion chamber. I have seen some very tight quench gaps. Personally, from what I have researched on it, we cannot go wrong with improvements in it. But as Kaase stated, most people are not willing to go through the effort and expense to do it.


As I understand it, the perfect chamber has the absolute minimum surface area, the idea being that chamber/piston area exposed to heat pulls heat away from combustion and therefore from application of its energy to moving the piston. On this aspect alone, leaving other complications and necessities aside, the perfect chamber would be a sphere.

[Reaper1]

i feel as if the swirl pistons with a g-head doesnt have a good quench area (because the dish is so large), but they seam to work good, not sure if its the low comp ratio or?

i ran a swirl head on g-head pistons and e85 with no intercooler (14.7psi) and made enough power to blow up the stock 525, which isnt saying much i guess? but it still felt pretty good, i wanted to take it farther, but went with the g-head/t3 piston motor while swapping in a 523 instead.

i think i might even try the swirl head on the t3 piston motor next, prob a little easier to get a tune for it i think... just worried about valve to piston issues...

I personally think the swirl head on g-pistons having good results is more of the lowered compression ratio (I got all messed up here and confused. This actually yields a HIGHER compression ratio, but the rest of my comment here still stands.) than any kind of increase in combustion efficiency. The only way to really tell would be to use EGT probes and monitor the A/F and the amount of fuel being used (either by a fuel flow meter or by calculating it using the pressure and pulse width at the injectors with the flow capacity of the injectors being a known). This would have to be done with a back-to-back test using both set-ups in each test, preferably on the same day. Increase in power or detonation resistance doesn't really tell the whole story.


As I understand it, the perfect chamber has the absolute minimum surface area, the idea being that chamber/piston area exposed to heat pulls heat away from combustion and therefore from application of its energy to moving the piston. On this aspect alone, leaving other complications and necessities aside, the perfect chamber would be a sphere.

This is where ceramic coating comes into play. :thumb:

[zin]

On this aspect alone, leaving other complications and necessities aside, the perfect chamber would be a sphere.

You'd be correct John, but there are other complications, some become big deals, others not so much.

An interesting mental exercise is to imagine this mirrored chamber, or spherical chamber being filled with high pressure gas, and how that force is acting on the pieces when they are "sealed up" at TDC, then imagine them pulling apart, and going back together.

It starts to become clear how timing, both physical positions and flame front become important factors.

For example, it is possible to have a chamber with lots of quench and the associated "squish"/tumble/swirl/turbulence that helps combustion and staves off detonation (the quench part), but if the timing is too early the end gasses could start to burn before the two halves get together to perform the quench, resulting in lots of HCs (from effective, but late quench) at best, and detonation at worst.

If the quench/squish is too aggressive, it could "blow out" the flame front as well, as the flame front will (within a certain degree) always burn at the same speed/rate, which is one of the reasons why big bores are difficult to make anywhere near as efficient as smaller bores, even though their larger surface area would tend to make them more desirable in most cases.

I'm not quite sure how I feel about the idea of holding the mix around the exhaust valve, I'm concerned that being in proximity to that much heat might destabilize the mix, resulting in detonation.

I do like the idea of pushing the spent gases out the exhaust with the chamber and piston shape, just not sure I'd work to concentrate the mixture in the hot spot... maybe if it were a very lean stratified charge...

Mike

[Shadow]

I personally think the swirl head on g-pistons having good results is more of the lowered compression ratio than any kind of increase in combustion efficiency.



Swirl head on G-pistons = Higher comp...........No? I did this years ago and the car went like a BOOH at 14 psi, everything else stock TII.

G head on Swirl pistons = Lower comp AFAIK.

- - - Updated - - -



If the quench/squish is too aggressive, it could "blow out" the flame front as well, as the flame front will (within a certain degree) always burn at the same speed/rate, which is one of the reasons why big bores are difficult to make anywhere near as efficient as smaller bores, even though their larger surface area would tend to make them more desirable in most cases.

Mike

This is a Good point, and one to keep in mind when building a boosted mtr.

[Vigo]

Swirl head on G-pistons = Higher comp...........No? I did this years ago and the car went like a BOOH at 14 psi, everything else stock TII.

I dont know what BOOH means but i assume it's good. My spirit has that combo and seemed pretty strong at 12psi for, like you said, stock tII everything else.

[OmniLuvr]

BAT OUT OF HELL :-)

and yes they do...

[Reaper1]

I think I actually tried the opposite combination, swirl pistons with a moderate port job and the chambers had been modified a little (laid the back wall by the valves back a bit to help unshroud the valves). That combination felt SO much faster at 10# than the original did at 14#. I will admit that I believe I made some other changes between set-ups that would most likely have that kind of effect as well.

Yes, I think the G-pistons with the swirl head would yield a higher static compression ratio. Please refresh my memory here. If IIRC the G-pistons have a dish that is smaller in diameter than the swirl pistons, and the dish is deeper, right? If this is the case, then that combination might be doing the altered squish area and charge volume control on a very basic, but what seems to be effective level. If so, that would be pretty sweet and kinda shows that the theory is sound.

[Shadow]

The biggest - for the swirl head vs the G-head IS how shrouded the valves are, so simply unshrouding them with no other work done will yield gains.

How much did the dynamic comp change from 85 (G-head) to 86+ (swirl)? We Know that the G-head has a significantly larger volume (cc's) chamber vs the swirl. So placing a stock swirl head on a G-head bottom end Will Increase the dynamic comp of That mtr.

What relation it will have to a regular swirl mtr we would need to bring more info into the fray, but I would be willing to bet that the swirl head + G-bottom end will still be Higher.

[Vigo]

I think the reason it isn't more common is that the g-pistons dont have proper valve reliefs for swirl head, which makes it interference. I have not tested this theory by breaking a belt yet. :p

[Shadow]

Common info on the 84-85 2.2l mtr is that Chrysler dropped the CR to 8.5:1 for turbocharging. When we bolted the swirl head on I'm pretty sure I cc'd the chambers and figured we would be up in the 8.8-9.0:1 range.

So, Chrysler would have had to drastically Increase comp on the swirl mtrs in order for them to be higher and I'm pretty sure (already having det. problems if proper octain not used) they Didn't.

Also, I seem to remember looking at the pistons and it seemed apparent (at the time) that the swirl mtr had the lower comp. pistons to make up the diff.

Someone jump in here and correct me if I'm Wrong!

[turbovanman²]

Swirl head on G-pistons = Higher comp...........No? I did this years ago and the car went like a BOOH at 14 psi, everything else stock TII.

G head on Swirl pistons = Lower comp AFAIK.

- - - Updated - - -



This is a Good point, and one to keep in mind when building a boosted mtr.

Booh as in crap or good? How can lower compression and a lazy chamber go better than a properly setup up TII? Everyone who has run a G-head on swirl pistons has noted, including me, they run like crap until the spark timing is changed.


Common info on the 84-85 2.2l mtr is that Chrysler dropped the CR to 8.5:1 for turbocharging. When we bolted the swirl head on I'm pretty sure I cc'd the chambers and figured we would be up in the 8.8-9.0:1 range.

So, Chrysler would have had to drastically Increase comp on the swirl mtrs in order for them to be higher and I'm pretty sure (already having det. problems if proper octain not used) they Didn't.

Also, I seem to remember looking at the pistons and it seemed apparent (at the time) that the swirl mtr had the lower comp. pistons to make up the diff.

Someone jump in here and correct me if I'm Wrong!

G head pistons have a very small dish, swirl head have a large dish. We had all the chamber CC's in the old KC but I guess we need to redo it again since its gone. G head on swirl pistons puts the compression down 1/2 a point.

I came up with this a few years ago-


Ok, these are averages and not exact, I worked out that its about 1 point using a TIII head on 2.5 pistons, TBI pistons are close to TIII pistons in dish volume and TBI's are 8.9:1 so based on that-

8 valve pistons, swirl head, 8.0:1
8 valve pistons, G-head, 7.5:1
8 valve pistons, TIII head, 7.0:1
8 valve pistons, Neon head, 8.0:1

TIII pistons, TIII head, 8.0:1
TIII pistons, swirl head, 9.0:1
TIII pistons, G-head, 8.5:1
TIII pistons, Neon head, 9.0:1

[Shadow]

Booh as in crap or good? How can lower compression and a lazy chamber go better than a properly setup up TII? Everyone who has run a G-head on swirl pistons has noted, including me, they run like crap until the spark timing is changed.

Not sure who your talking to here? No one is talking about a G-head on a swirl bottom end, the conversation is about the Opposite; Swirl head on a G-bottom end! :)




G head pistons have a very small dish, swirl head have a large dish. We had all the chamber CC's in the old KC but I guess we need to redo it again since its gone. G head on swirl pistons puts the compression down 1/2 a point.

I came up with this a few years ago-

Well, if that's true it would Support what I'm saying; IF the G-head Drops comp by 1/2 point, then the reverse would also be true; that the swirl would Increase it by 1/2 point making the Swirl + G bottom end 9.0:1 comp. (I guestimated 8.8-9.0:1 with that combo)

So your Agreeing with me :)

- - - Updated - - -




Yes, I think the G-pistons with the swirl head would yield a higher static compression ratio. Please refresh my memory here. If IIRC the G-pistons have a dish that is smaller in diameter than the swirl pistons, and the dish is deeper, right? If this is the case, then that combination might be doing the altered squish area and charge volume control on a very basic, but what seems to be effective level. If so, that would be pretty sweet and kinda shows that the theory is sound.

You confused me earlier by saying the the Swirl head on G-bottom end = Lower comp. So now your saying the opposite, that it would yield Higher comp? (so agreed?)

That being said, and if it holds true, how could we possible know that Any benefit from squish is being had? Don't you think the simple answer to the gained "feel" of performance would be the raised comp?

Don't get me wrong, I would love to agree with you guys about this, but I believe it's a waisted venture in a highly boosted engine. Your making the mtr Work Harder, and at 2-3 x atmospheric pressure the Squish is no longer "as relevant".

- - - Updated - - -




Warren Stramer is running his pistons down in the hole by a bit (similar to the NSRT 2.4 Turbo) and when asked about it he responded that he has noticed a current trend for high performance FI engines to not be using squish much, if at all. While I can't argue with his results, knowledge, or skills, I can't agree with that thinking simply because it doesn't make much sense if you look at the "problem" from an engineering physics point of view. Maybe I'm all "starry eyed", and have fallen prey to an elaborate gimmick, but I've seen the results from using this train of thought in practice, and I've had other very experienced engine people agree with it as they'd also messed with portions of the idea and seen results themselves. Also, given that new, high efficiency engines are employing this type of design (which Larry and his company have been contracted by auto makers to develop products for them)...I can't help but to believe this is the way to go.

When you say "down in the hole a bit", what are we talking here? Stock height, lower, or is this simply a reference to anything run "under deck height"?

Not being a smart a$$, just trying to get some clarafication, cause I'm Not aware of Warren running his pistons any lower than one normally would.

[Reaper1]

Yeah, I think I'm getting all messed up with the different combo's now! LOL

So, I went back and re-read some stuff! :)

I agree that G-head on swirl pistons should yield a lower compression ratio. I have no clue why I thought anything different! LOL I did, however, bring up the G-head on the swirl bottom end. That is what I was talking about that I ported and de-shrouded the valves. (I think....man, now I'm second guessing myself...that was back in 2000) Maybe this came from the train of thought back at the time that the G-head was the way to go because of the huge chamber and lower compression to help with detonation because good engine management wasn't really around yet. Now I'm thinking I went away from that convention and DID stick with the swirl head. I know I used the FelPro "head saver" shim to lower the compression ratio at that time.

I know as time went on I kept leaning more towards the swirl head while others were still poo-pooing it. I also know I was recognizing that the pistons were a really crappy design (though I never did get to pulling the trigger on my design :( ).

For mixing stock designed parts, I agree that the G-pistons with the swirl head is probably a good place to start. It seems a few have had success using a flat, or near flat-top piston as well. I can see how that would also yield some good results.


That being said, and if it holds true, how could we possible know that Any benefit from squish is being had? Don't you think the simple answer to the gained "feel" of performance would be the raised comp?

By doing this:
The only way to really tell would be to use EGT probes and monitor the A/F and the amount of fuel being used (either by a fuel flow meter or by calculating it using the pressure and pulse width at the injectors with the flow capacity of the injectors being a known). This would have to be done with a back-to-back test using both set-ups in each test, preferably on the same day. Increase in power or detonation resistance doesn't really tell the whole story.
I also need to say that monitoring spark advance needs to be added in there. Technically and theoretically speaking, the less advance you have to run, the better because the charge is able to combust more quickly and efficiently with a good design.


When you say "down in the hole a bit", what are we talking here? Stock height, lower, or is this simply a reference to anything run "under deck height"?

From my understanding, the stock 2.4 turbo engines (NSRT-4, PTGT), at TDC the piston crowns do not come up to the block deck height. To me, this is "down in the hole".

[Shadow]

Yeah, I think I'm getting all messed up with the different combo's now! LOL

So, I went back and re-read some stuff! :)

I agree that G-head on swirl pistons should yield a lower compression ratio. I have no clue why I thought anything different! LOL I did, however, bring up the G-head on the swirl bottom end. That is what I was talking about that I ported and de-shrouded the valves. (I think....man, now I'm second guessing myself...that was back in 2000) Maybe this came from the train of thought back at the time that the G-head was the way to go because of the huge chamber and lower compression to help with detonation because good engine management wasn't really around yet. Now I'm thinking I went away from that convention and DID stick with the swirl head. I know I used the FelPro "head saver" shim to lower the compression ratio at that time.

I know as time went on I kept leaning more towards the swirl head while others were still poo-pooing it. I also know I was recognizing that the pistons were a really crappy design (though I never did get to pulling the trigger on my design :( ).

For mixing stock designed parts, I agree that the G-pistons with the swirl head is probably a good place to start. It seems a few have had success using a flat, or near flat-top piston as well. I can see how that would also yield some good results.

Ha, ya I figured things were getting pretty mixed up and confused when Simon came on bourd and started talking about g-head/swirl bottom end combos and I'm like, WTH? I thought we were talking about swirl heads on G-bottoms! lol

Glad I didn't waiste any more time on that one!




By doing this:
I also need to say that monitoring spark advance needs to be added in there. Technically and theoretically speaking, the less advance you have to run, the better because the charge is able to combust more quickly and efficiently with a good design.

Fair enough, but to what end? Let's just say that Some efficiency Could be had from this. So you design a custom piston, install it above the deck and raise the Dynamic compression to a level that makes the mtr No longer user friendly?

So now what? Design a custom cam to try and change the timing events to bring Down the Static compression to a level where you won't have to run pure alcohol or 118+ octain to drive anywhere?

What are you planning to do with the crazy comp that is inherently going to go hand in hand with this modification?

I'm Not trying to be pessimistic here either, just looking for the Practical end to this. :)

Now if one or several of you are simply Driven to "Have to know" (like myself and a few others around here) than I already know that Nothing I can say will dissuade you and Good luck and I look forward to your results.

I will agree than in a 1 off all out drag car that is trying to gain Every possible advantage with No regard to expense and time, this may be worth persuing. (then again, it just may Not be :()

Now remember, part 2 of what I feel is Great about a car like the Charger is it can go 9's at the track, then get 40 MPG cruising home on pump premium! lol

Now that's just me, maybe you guys have other goals in mind?



From my understanding, the stock 2.4 turbo engines (NSRT-4, PTGT), at TDC the piston crowns do not come up to the block deck height. To me, this is "down in the hole".

OK, I kind of thought that's what you may have ment. So all of our 2.2/2.5 mtrs are "down the hole" according to that thinking. Because you specifically mentioned the NSRT-4, I thought you may have been talking something beyond what one of our "stock" built mtrs would be running. (further down than normal)

- - - Updated - - -


While there is no doubt squish is important N/A, the question is, at what boost level and circumstances might it become a negative. It seems there might be a point when there can be too much turbulence.

Thanks
Randy

I would have to Agree with this statement! Maybe in a low boost application like the Omni last year that was trying to run a monster turbo out of its efficiency at 10psi boost, you may see a significant improvement. Also IF your mindset is running on the ragged edge of timing in an effort to make more power on less boost. This may be the way to go.

But, with the understanding that the Amount of boost is irrelevant, really only a # for reference, and the Real Focus is what is happening in the cylinder, (cylinder pressure = Power) your always going to want to run as Much Boost as your set-up can and This Will Increase the turbulence at the opening of the intake valve.


By how much? Enough that most ppl "in the know" have come to regard "squish" as no longer needed like an N/A mtr and move their attention to the benefits of "not running squish".

[Reaper1]

I'm not saying that the high squish design HAS to have some sort of abnormally high CR or that the piston has to stick up out of the hole. The goal can be accomplished without having a static CR through the roof.

The goal is to control the charge and place it in the chamber where you want it while keeping it homogeneous.

Here, take a look at these:

These are listed as 2002 Eclipse FI (left) and high compression (rt)
http://www.theoldone.com/components/pistons/2002_Eclipse_1.jpg

This is for the 6G72 twin turbo
http://www.theoldone.com/components/pistons/3000GTTurbo.jpg

2JZ turbo
http://www.theoldone.com/components/pistons/2JZ06.jpg

All of those pistons are designed with the high squish and charge control that I'm talking about. For the most part, the Honda pistons for FI max out at around 10:1 give or take. There is one combination that is 11:1. Most are in the 9's. However, with this design fully implemented (meaning correct porting and correct chamber shape) the compression ratio isn't the deal breaker it once was because you have more control of the charge.

Yes, there is a limit for pump gas, I agree 100%. The beauty is that you can now make more power with pump gas than you were before, and probably do it using LESS fuel and LESS boost (or more accurately less air)! I don't see a downside.

With control over the charge placement and everything mechanically lending itself to a more efficient burn, ignition timing advance should DECREASE. That's not a bad thing either. That means there is less time the engine is having to work against the burning charge, freeing up more power and helping the engine to react faster.

Turbulence at the valve opening helps, for sure, but what happens to the charge AFTER the valve once it's in the chamber? Turbulence only lasts so long if there isn't something to keep it going. I really want to set up an experiment now to demonstrate this.

Anyway, the point is that if you can control the charge you introduce into the chamber while keeping it all mixed up and make sure that it is the cleanest charge you can have (something else high squish helps with, remember), you will be able to get more power out of that charge that if you otherwise just let it "roam free".

[GLHS60]

Well said!!!

Thanks
Randy


[/QUOTE] By how much? Enough that most ppl "in the know" have come to regard "squish" as no longer needed like an N/A mtr and move their attention to the benefits of "not running squish".[/QUOTE]

[Shadow]

I'm not saying that the high squish design HAS to have some sort of abnormally high CR or that the piston has to stick up out of the hole. The goal can be accomplished without having a static CR through the roof.

The goal is to control the charge and place it in the chamber where you want it while keeping it homogeneous.

Here, take a look at these:

These are listed as 2002 Eclipse FI (left) and high compression (rt)
http://www.theoldone.com/components/pistons/2002_Eclipse_1.jpg

This is for the 6G72 twin turbo
http://www.theoldone.com/components/pistons/3000GTTurbo.jpg

2JZ turbo
http://www.theoldone.com/components/pistons/2JZ06.jpg

All of those pistons are designed with the high squish and charge control that I'm talking about. For the most part, the Honda pistons for FI max out at around 10:1 give or take. There is one combination that is 11:1. Most are in the 9's. However, with this design fully implemented (meaning correct porting and correct chamber shape) the compression ratio isn't the deal breaker it once was because you have more control of the charge.

Yes, there is a limit for pump gas, I agree 100%. The beauty is that you can now make more power with pump gas than you were before, and probably do it using LESS fuel and LESS boost (or more accurately less air)! I don't see a downside.

With control over the charge placement and everything mechanically lending itself to a more efficient burn, ignition timing advance should DECREASE. That's not a bad thing either. That means there is less time the engine is having to work against the burning charge, freeing up more power and helping the engine to react faster.

Turbulence at the valve opening helps, for sure, but what happens to the charge AFTER the valve once it's in the chamber? Turbulence only lasts so long if there isn't something to keep it going. I really want to set up an experiment now to demonstrate this.

Anyway, the point is that if you can control the charge you introduce into the chamber while keeping it all mixed up and make sure that it is the cleanest charge you can have (something else high squish helps with, remember), you will be able to get more power out of that charge that if you otherwise just let it "roam free".

It all sounds good and looks good and like I said earlier, in certain applications I'm sure it will work well. Maybe that's where this becomes lost on me. Application!

So again, in a lower boosting application (10-15psi? Maybe lower yet?) I see this having a benefit. What is not clear to me is wether or not there is any benefit left at say, 25+psi where you have 2-3 x Atmospheric pressure + Working for you when the intake valve opens. Creating 2-3 times the "tumble" Through the valve and into/around the chamber. This Is the benefit of running higher boost........no?

Now, in an application where you want to put something together and run it at a certain boost pressure, let's say 15psi Max. I'm sure that this is 1 of the aspects of that type of build that will help you achieve Better power and efficiency in That boost range. (I don't really know What boost range it would be relevant) The problem with this type of build is you can get Lost on the turbo selection and end up moving Backward in over-all efficiency, loosing the "dynamic" of the system as a whole.

Maybe this is what most are looking/hoping for?

I have never "bought into" that way of thinking. For me, boost #'s are just a reference, a reference to how efficient the entire system is working according to the specific turbo Specs the system is running. Once I know the exact spec of the turbo, cold And hot side, I can look at the map, then look at what the most efficient set-up has made with that specific turbo, and see clearly where the system is at, with the understanding that in order to Really know where things are is to "run out the turbo".

Since my goal will alway be to run out the turbo in order to See Real world efficiency And, to see just how well matched my turbo is to my system, I will always be running 25-40psi boost and as far as I can see, there is no benefit to squish in such an application. (for reasons stated earlier)

Having said all this; If you can prove it wrong and come up with a piston design that incorporates squish and works to increase efficiency to 30psi boost, I'm all for it! :nod: and if the dynamic CR could be kept to say 10:1 or less, all the better.

Keep in mind that all this "thinking" is done with my "Lizard brain", so it may be too simplistic for some to digest. :)

[zin]

Fair enough, but to what end? Let's just say that Some efficiency Could be had from this. So you design a custom piston, install it above the deck and raise the Dynamic compression to a level that makes the mtr No longer user friendly?

If one is having a custom piston made, simply specify the pin height that will place the crown where you want it, and design the dish to provide the desired compression, and if possible, motion of the mixture.

None of this should make the engine any less user friendly... Unless you're referring to the fact that the added efficiency will necessitate the ignition timing be re-curved to match the improved combustion efficiency, but it seems like that shouldn't be that big a deal for someone willing to get this far into engine modifications.

As far as boost levels go, higher boost levels correlate to higher restrictions and the higher velocities that come with it. I can see how it can be used to maintain motion in the mixture, but I don't think it'll be nearly as effective as a mechanical "squish".

Disregarding squish for a minute, a more critical detail, especially at high boost, will be detonation resistance, which is what quench is going to provide. It effectively shrinks the active combustion space, reducing the saturation time the mixture sees. Additionally the smaller combustion space makes for a quicker/more efficient burn, even if squish isn't present.

In the end, quench/squish is worth perusing, but isn't an answer for all that ails you.

Mike

[Reaper1]

If one is having a custom piston made, simply specify the pin height that will place the crown where you want it, and design the dish to provide the desired compression, and if possible, motion of the mixture.

None of this should make the engine any less user friendly... Unless you're referring to the fact that the added efficiency will necessitate the ignition timing be re-curved to match the improved combustion efficiency, but it seems like that shouldn't be that big a deal for someone willing to get this far into engine modifications.

As far as boost levels go, higher boost levels correlate to higher restrictions and the higher velocities that come with it. I can see how it can be used to maintain motion in the mixture, but I don't think it'll be nearly as effective as a mechanical "squish".

Disregarding squish for a minute, a more critical detail, especially at high boost, will be detonation resistance, which is what quench is going to provide. It effectively shrinks the active combustion space, reducing the saturation time the mixture sees. Additionally the smaller combustion space makes for a quicker/more efficient burn, even if squish isn't present.

In the end, quench/squish is worth perusing, but isn't an answer for all that ails you.

Mike

^^ This.....that is all. :thumb:

[Shadow]

Not much more to ad to this, but I will say that when I originally got into turbo charging, my views we different that most. While others seemed to think that a turbo mtr is a Completly Different beast, I believed it was simply an N/A mtr with a snail attatched to it.

That is to say, take the most efficient N/A build, pick the right turbo and tune = the most efficient Turbo mtr also.

All these years later and for the most part, that has held true. I regard squish as one of the few eg that Maybe, Just maybe there are things that Are different for a turbo mtr? But wait a second, that's what I had thought about cams, before I tried the F4 cam. lol

Now I stuck with the stock cam because in my early years of building these mtrs it seemed like the ppl who were "in the know" had proven that higher lift cams Don't work at high boost. (so I got stuck in a mind-set) We ALL know now that it was Not true!

So who knows; there Is one eg that has intrigued me for these past several years, and that's the 4G63 builds from Spiros in Greece. 13.5:1 comp Turbo mtrs making 1500+WHP! His set-ups are definatly using Squish/Quench and obviously working. Although Everything included in those builds is priced beyond anything I will ever be able to muster in my whole life :(

So at the top, top end of insanity there is a glimmer of hope that this could all come true, but to bring it all down to practicle application is where the Real work begins and at a practicle Cost! (many of those mtrs have a life of 120hrs or less :()

I have Never had any issues with detonation being a problem with the Charger, and never really had any issues with the entire system working as a whole. So like they say, if it ain't broke..............

There are So many other basics that this community needs to get down before looking into stuff like this that it's not even funny. Most can't even hold one of these mtrs together for a year and are Still having trouble with simple tuning :(

So again, Not saying don't give it a try, just stating Why it has No appeal to Me at this point in time. Have fun and be safe out there!

Rob out..............

[Force Fed Mopar]

That is the consensus of many EMC builders as well.

[Aries_Turbo]

My question about those that have tried mix and match combos and came to the conclusion that it was faster or better. How many of those kept an eye on knock retard values or a actual ignition advance going into the engine?

Did the combo actually perform well or was it relying on the knock sensor to survive. Just some stuff to think about.

[OmniLuvr]

Did the combo actually perform well or was it relying on the knock sensor to survive. Just some stuff to think about.

so then that would just be a problem of getting the right tune?

i havent had any problems with my knock light coming on, but i also havent checked the scanner either. i have a 3 bar some sort of stage 5 g-head cal (a shelgame cal but not from shelgame himself) set to run on e85 and +40's, it gets the job done, really need to hit the dyno, but want to put a front mount on it first, i think the stock cooler is really holding me back...

[Aries_Turbo]

so then that would just be a problem of getting the right tune?

i havent had any problems with my knock light coming on, but i also havent checked the scanner either. i have a 3 bar some sort of stage 5 g-head cal (a shelgame cal but not from shelgame himself) set to run on e85 and +40's, it gets the job done, really need to hit the dyno, but want to put a front mount on it first, i think the stock cooler is really holding me back...

yes, having the calibration dialed in to your exact setup is key to making it last and getting all the benefits of the physical combination of parts.

see the stock restrictive cooler could be keeping the airflow down enough that the cal is pretty close. uncork that and it could go lean.

Brian

[GLHS60]

Back to the original topic I built my Super 60 Omni engine with .035 squish and is reasonably detonation friendly. I can run as much as 24 psi on pump gas depending on weather etc. and after 14 years I finally blew one headgasket. However running .035 squish means my pistons are .033 "proud" or above the deck. I have been thinking about why Chrysler always always runs turbo pistons so far below the deck totally ignoring the squish theory. It occurs to me they may be more interested in crevice area/volume than squish. Crevice is totally minimized with the piston below the deck. With the piston proud the crevice now includes the headgasket bore which is about 3.540 over a 3.445 bore and worse yet the piston crown is usually about .030 smaller than the bore so the crevice area/volume increases drastically. The crevice is the area/volume above the top ring to the top of the piston and is detrimental to a good burn.

Thanks
Randy

[Ondonti]

The high top 6g72 style piston was used in a 2 valve setup by Sunmind for a 3000gt (similar type build to the Rick Lozier 3.0) and he seemed to think he needed to run race gas and that the piston top was causing combustion problems (flame front propagation). 2 valve 6g72 has the spark plug biast to the exhaust valve where the 4 valve is more centralized.

13.5:1 compression on 100% methanol fueling is not really comparable since that stuff is not going to detonate no matter how bad your chamber is. At that point I think the challenge is being able to light off the mixture.

For a 2 valve with moderate compression levels (like 9:1) I would have a slanted dish that diverged slowly from the quench area farthest from the plug and deepened near the plug. I am not into those extreme valve reliefs if your motor is going to be interference anyways. Are those 4g64 eclipse pistons or 6g72. Big difference. Not sure if the valve faces are closer to the piston on one motor than the other.

[Reaper1]

Back to the original topic I built my Super 60 Omni engine with .035 squish and is reasonably detonation friendly. I can run as much as 24 psi on pump gas depending on weather etc. and after 14 years I finally blew one headgasket. However running .035 squish means my pistons are .033 "proud" or above the deck. I have been thinking about why Chrysler always always runs turbo pistons so far below the deck totally ignoring the squish theory. It occurs to me they may be more interested in crevice area/volume than squish. Crevice is totally minimized with the piston below the deck. With the piston proud the crevice now includes the headgasket bore which is about 3.540 over a 3.445 bore and worse yet the piston crown is usually about .030 smaller than the bore so the crevice area/volume increases drastically. The crevice is the area/volume above the top ring to the top of the piston and is detrimental to a good burn.

Thanks
Randy

Stock 2.2 turbo pistons aren't that far below the deck, if at all, but the "crevice" is pretty darn huge for a "modern" engine. The ring pack sits a pretty good ways down.

I do agree that this can have an adverse effect on burn quality, but it serves 2 main purposes: it helps protect the top ring and it adds strength to the piston crown.

Compare the robustness of the cast 2.2 vs. 2.5 common block pistons in this area and you'll immediately see what I'm talking about.


The high top 6g72 style piston was used in a 2 valve setup by Sunmind for a 3000gt (similar type build to the Rick Lozier 3.0) and he seemed to think he needed to run race gas and that the piston top was causing combustion problems (flame front propagation). 2 valve 6g72 has the spark plug biast to the exhaust valve where the 4 valve is more centralized.

13.5:1 compression on 100% methanol fueling is not really comparable since that stuff is not going to detonate no matter how bad your chamber is. At that point I think the challenge is being able to light off the mixture.

For a 2 valve with moderate compression levels (like 9:1) I would have a slanted dish that diverged slowly from the quench area farthest from the plug and deepened near the plug. I am not into those extreme valve reliefs if your motor is going to be interference anyways. Are those 4g64 eclipse pistons or 6g72. Big difference. Not sure if the valve faces are closer to the piston on one motor than the other.

What pictures are you asking about?

I agree that if the engine is going to be interference, then the only reason to have valve reliefs on the piston is to make sure the valve doesn't hit it during normal operation. Cutting huge pockets in the pistons just to make it non-interference will probably do more harm than good for combustion efficiency.

[4 l-bodies]

Stock 2.2 turbo pistons aren't that far below the deck, if at all, but the "crevice" is pretty darn huge for a "modern" engine. The ring pack sits a pretty good ways down.

I do agree that this can have an adverse effect on burn quality, but it serves 2 main purposes: it helps protect the top ring and it adds strength to the piston crown.

Compare the robustness of the cast 2.2 vs. 2.5 common block pistons in this area and you'll immediately see what I'm talking about.

Every bone stock 2.2 & 2.5 8V motor I have measured during disassembly is at a minimum .010 down the hole. Maximum has been about .015. Average is about .012". That isn't much below deck?
Todd

[Reaper1]

Not compared to 1/4" ;)

[contraption22]

Bringing this thread back from the dead because it came up in Google searching.
Seems like the general consensus is that .040 is the safe piston-to-head clearance number to shoot for for a street engine with steel rods. JE pistons recommends this much clearance. Balls-out race engines can go tighter, but less than .035 is cutting it close. You also have to take piston rock into consideration.

Has anybody here run tighter than that with success?

[ShelGame]

I think the reason it isn't more common is that the g-pistons dont have proper valve reliefs for swirl head, which makes it interference. I have not tested this theory by breaking a belt yet. :p

Really? That's good to know. I'm putting a ported swirl head on a 2.2 T1 bottom end for my GLH (with HD rods).

I missed this thread first time around (or forgot about it). Good read!

[Aries_Turbo]

You going to measure with clay or something if there is enough clearance rob?

[contraption22]

You going to measure with clay or something if there is enough clearance rob?

Should be able to measure it with a dial caliper, as long as the crushed thickness of the head gasket is known.

[turbovanman²]

That's how I did it, used clay, then used some vernier calipers, worked like a charm.

[contraption22]

I'm not understanding the need for clay.

[Aries_Turbo]

put clay on the piston. oil face of valve. install head and used headgasket. torque head.

rotate crank to highest piston. rotate cam.

remove head. measure squished clay spot to see if there is adequate clearance from piston to valve.

Brian

[contraption22]

put clay on the piston. oil face of valve. install head and used headgasket. torque head.

rotate crank to highest piston. rotate cam.

remove head. measure squished clay spot to see if there is adequate clearance from piston to valve.

Brian

Ah that makes sense for piston to valve. I was still on squish.

[Force Fed Mopar]

Could be used to measure squish probably also.

[contraption22]

Could be used to measure squish probably also.

I suppose. I've been doing a lot of reading on this (unfortunately) and really the best way is piston deck height + head gasket compressed thickness.
So if your piston is .005 down in the bore, and your gasket is .035 thick, you have .040 clearance.
If your piston is .010 above the deck, and your gasket is .040, you have .030 clearance.

[mopar-tech]

put clay on the piston. oil face of valve. install head and used headgasket. torque head.

rotate crank to highest piston. rotate cam.

remove head. measure squished clay spot to see if there is adequate clearance from piston to valve.

Brian

I perfer checker springs myself, clay does have its uses time to time.

- - - Updated - - -


I suppose. I've been doing a lot of reading on this (unfortunately) and really the best way is piston deck height + head gasket compressed thickness.


Check over on Moparts Mike, there is usally lots of discussion on the subject with the B/RB crowd. Mike correct on how to check for squish and it is the way most people usally verify.

[Aries_Turbo]

I perfer checker springs myself, clay does have its uses time to time.

like a light spring? so you rotate the cam to max lift and the crank to TDC and then push down on the valve to check to see if there is clearance?

that does sound easier than clay lol.

Brian

[mopar-tech]

like a light spring? so you rotate the cam to max lift and the crank to TDC and then push down on the valve to check to see if there is clearance?

that does sound easier than clay lol.

Brian

Yes.

You setup the cylinder you are checking and install a dial indicator on the valve retainer and just push down on the valve at any point in the cycle to see how much clearance you have.

[Aries_Turbo]

Yes.

You setup the cylinder you are checking and install a dial indicator on the valve retainer and just push down on the valve at any point in the cycle to see how much clearance you have.

oooh. :) ill have to get some of these if i do a 16v conversion. :)

thanks

Brian

[Force Fed Mopar]

The cam degree kit I bought from Summit came with a checker spring.

[johnl]

Back to the original topic I built my Super 60 Omni engine with .035 squish and is reasonably detonation friendly. I can run as much as 24 psi on pump gas depending on weather etc. and after 14 years I finally blew one headgasket. However running .035 squish means my pistons are .033 "proud" or above the deck. I have been thinking about why Chrysler always always runs turbo pistons so far below the deck totally ignoring the squish theory. It occurs to me they may be more interested in crevice area/volume than squish. Crevice is totally minimized with the piston below the deck. With the piston proud the crevice now includes the headgasket bore which is about 3.540 over a 3.445 bore and worse yet the piston crown is usually about .030 smaller than the bore so the crevice area/volume increases drastically. The crevice is the area/volume above the top ring to the top of the piston and is detrimental to a good burn.

Thanks
Randy



On the first page of this thread, FiveDigits and 4LBodies both recommended milling the deck and, reading between the lines, I took it that reducing the volume of gasses trapped in what Randy calls the "crevice" helps control detonation.

I took it that way because that is the difference between milling the head and milling the deck.


Five Digits -
http://www.turbo-mopar.com/forums/showthread.php?71207-Running-035-quot-Squish-In-8V-Cylinder-Head&p=994568&viewfull=1#post994568


4LBodies -
http://www.turbo-mopar.com/forums/showthread.php?71207-Running-035-quot-Squish-In-8V-Cylinder-Head&p=994602&viewfull=1#post994602

[GLHS60]

I'm glad you revived this old thread!!

My crevice area thoughts have been confirmed as some racing pistons are now using anti-detonation grooves.

Thanks
Randy

http://www.cp-carrillo.com/gi-255687-anti-detonation-grooves-contact-reduction-grooves.html

PS: Can you see the picture?

62318

[zin]

Here's a good read: http://www.msbr.com.br/Documentos/pistonsquish.pdf

I was looking at it from a "chamber softening" for nitrous standpoint, but the data is good data, regardless of application.

Mike

[Reaper1]

That was a REALLY good read! Thanks!

[zin]

Some pretty interesting results in there, eh?:)

Mike

[Reaper1]

I want more! LOL I had heard of this, but I had a different mental image of what it meant. I understood what was going on, but not exactly how. I'd really like to see this study done with all kinds of designs. One thing I did notice is that the study was focused more on partial/light loading than all out power. I get that these ideas help combustion and such, but I wonder if or how much they break down when at max load?

[GLHS60]

And that's the question!!!

Thanks
Randy




. I get that these ideas help combustion and such, but I wonder if or how much they break down when at max load?

[Ondonti]

I want more! LOL I had heard of this, but I had a different mental image of what it meant. I understood what was going on, but not exactly how. I'd really like to see this study done with all kinds of designs. One thing I did notice is that the study was focused more on partial/light loading than all out power. I get that these ideas help combustion and such, but I wonder if or how much they break down when at max load?

Pretty sure I been telling you this is all bad for racing right?

This paper is chasing efficiency. Efficiency means avoiding knock at light load situations to allow running as lean as possible while still meeting emissions targets. I am interested by that deep piston, in that it made for unstable combustion at light loads. I wonder how it behaves at high load? Not a good piston design weight wise unless its a factory cast piston. Forged they would have to use a super thick crown.

In a full load setup, that "late knock" is not what you are aiming to avoid. You are trying to avoid peak cylinder pressure spikes. The poor combustion of the large chamber flat top piston is lovely under high load. The efficient setup gets too efficient at high load.

When the 8 valve turbo was designed, turbochargers of small size usually couldn't even be mapped above 30psi, cause they just didn't work up there. CAD designed billet compressor wheels can make 4-5 bars of pressure or more these days.

My point here being that an engine optimized for n/a performance running 1 bar of boost is not "that far" out of its comfort zone. Try running 45psi boost on that engine now. Would you rather run 45 pounds of boost, or 25 because your chamber is killing you?

------------------------------

[Ondonti]

Here's a good read: http://www.msbr.com.br/Documentos/pistonsquish.pdf

I was looking at it from a "chamber softening" for nitrous standpoint, but the data is good data, regardless of application.

Mike

They are doing the opposite! Putting together and order for a soft piston right now btw...

[Force Fed Mopar]

I know on my stock swirl head, above 15ish psi there were a lot of lower rpms at 1 degree total timing and I was running 10.6-10.8 on my wideband.

[Reaper1]

I know on my stock swirl head, above 15ish psi there were a lot of lower rpms at 1 degree total timing and I was running 10.6-10.8 on my wideband.

Was there any knock count?

[Force Fed Mopar]

I didn't really log it, but I don't think so. I had to modify the knock threshold for some engine noise and higher boost level. I ran it that way for 3 years after tuning it, never missed a beat, and the pistons look great still. Also the rod bearings looked like new still. So I feel confident in saying it never knocked...

I do know that if I tried to run it at 11.5-11.8 on my wideband, then I would start seeing the CEL flash in higher boost. 10.6-11.0, no issues.