Running .035" Squish In 8V Cylinder Head

[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/sh...l=1#post994568


4LBodies -
http://www.turbo-mopar.com/forums/sh...l=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...n-grooves.html

PS: Can you see the picture?

[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?

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