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Old 09-17-2012   #1
Halon
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Squish Band / Quench

This is something I've never really paid much attention to until recently, and I'd bet I'm not the only one here in that boat. So figured I'd throw up some info I found on some of the Toyota forums in case it's useful to anyone on here. Sorry it's mostly going to be 2JZ specific numbers, but quench theory in general applies to most motors so might be useful to some on here if you just plug in the 4G63 numbers.

All credit for this info goes to SuperStock and JGSupraTT.




Squish band or Quench is the area between the flat of the piston and the flat of the cylinder head at TDC. It is generally accepted that .032”(.8mm) is the minimum safe piston to cyl head clearance. It is also generally accepted that when the piston to cyl head clearance exceeds .060”(1.5mm) the squish effect is severely diminished. Some side effects of too high of a quench area consist of increased heat, and increased risk of detonation.

There are 3 things that matter when calculating the squish.
1. Where the top of the piston sits relative to the deck of the engine.
2. The compressed headgasket thickness.
3. Flush or recessed combustion area on the head (2jz-ge=.030" recess, 2jz-gte=0 recess).

The 2JZ-GTE and 2Jz-GE pistons both are .005" below the deck in our engines at TDC.

The compressed headgasket thickness is either 0.050" (GTE) or 0.010" (GE).

Which head you are using is important because on the GE head, the combustion chamber is recessed 0.030" compared to no recession in the GTE head. This means the GE head will increases the distance between the flat of the piston and flat of the cylinder head (ie. increased squish).

PIC OF RECESSED GE HEAD vs. NO RECESS GTE HEAD
GE Recessed:
http://i1196.photobucket.com/albums/...tonchamber.jpg
http://i1196.photobucket.com/albums/...ionchamber.jpg

GTE no recess:
http://i1196.photobucket.com/albums/...tonchamber.jpg
http://i1196.photobucket.com/albums/...ionchamber.jpg

At this point it is simple math (piston to deck distance + compressed HG + head recess)

2JZ-GE = .005 + .010 + .030 = .045"
2JZ-GTE = .005 + .050 + .000 = .055"




So with that all being said, a couple little things I found out about the various generations of the 4G63. These numbers below were pulled from the internets, so if anyone has real numbers they've actually measured, feel free to chime in.

Early 4G63's = .015 deck height +.050 HG = .065"
Evo 8 = .070 deck height + .035 HG = .105"
Evo 9 is = ??? deck height + .049 HG = ??? (.119" if deck is same as evo 8)


I thought that was interesting, because that would imply Mitsubishi engineers basically don't give a crap about quench theory. Maybe this is why certain shops (Magnus) have come up with specialized piston designs that they claim improve the quench band?

Anyhow, food for thought that I thought I'd share. Maybe some smarter people on here will chime in with their thoughts.
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Old 09-17-2012   #2
goodhart
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Re: Squish Band / Quench

Interesting. Nice post man
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