Running .035" Squish In 8V Cylinder Head

[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