Thicker Head Gaskets with Hi Boost applications
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From: Forced Induction Heaven
Thicker Head Gaskets with Hi Boost applications Anybody use thick head gaskets like around .070". I have the 2002 MLS Head Gaskets (which I think are great as they sustained 16lbs of boost with ARP Head Studs) but my CR is 9.7:1 and I was toying with the idea of using a thicker head gasket to drop the CR. Any ideas???
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From: Forced Induction Heaven
Originally Posted by INTMD8
Thicker head gaskets are not the way to go. You will lower the compression, but you will increase quench distance so much that you will be more likely to have detonation problems.
Yeah thats what I thought....the quench/squish area is critical to everthing working correctly.
Thanks
bah mine are .067" thick, less then .9 degrees max knock retard with 94 octane and hot outside. stock thickness is around .057 so that much shouldnt hurt.
I do agree dont go to thick it is better to lower it through pistons, but a few points wont hurt, i thick someone is running .078's with no adverse effects shown, aka mello yello
I do agree dont go to thick it is better to lower it through pistons, but a few points wont hurt, i thick someone is running .078's with no adverse effects shown, aka mello yello
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From: College Station, Tx
Quench is basically the distance from the top of the piston to the bottom of the head. You can figure it as
Headgasket Thickness(compressed) + (Block Deck Height - (Rod Length + 1/2*Stroke + Piston Compression Height))
If you know where the piston is with relation to the deckheight you can replace the whole second term with that - on a stock LS1 shortblock it's about 0.007 out of the whole, so the second term would be -0.007 - so if a stock headgasket is 0.057, your stock quench is about 50 thousandths.
smokinHawk: So how do you know you wouldn't have 0 knock retard and be able to run more timing if you had a proper quench? It's not voodoo or anything else, it's pretty much a basic fact. You can get your quench large enough that it doesn't matter anymore (motor becomes a "non-quench" design - you have to be over 0.1 or so for this to work - some of the Dodge Magnum motors are like this) - but ideally I would build a normal quench motor - and all the values here are in that range anyway.
A larger quench doesn't mean you will blow up right away, but it will hurt your octane tolerance - you may improve it (octane tolerance) by reducing compression, but you will hurt it with a larger quench - so in the end it may be a wash - you could have made more power at the same octane level with a smaller quench/higher compression.
The best bet is to set your compression with the heads/pistons, and keep your quench between 0.035-0.040 or 0.045 or so.
Headgasket Thickness(compressed) + (Block Deck Height - (Rod Length + 1/2*Stroke + Piston Compression Height))
If you know where the piston is with relation to the deckheight you can replace the whole second term with that - on a stock LS1 shortblock it's about 0.007 out of the whole, so the second term would be -0.007 - so if a stock headgasket is 0.057, your stock quench is about 50 thousandths.
smokinHawk: So how do you know you wouldn't have 0 knock retard and be able to run more timing if you had a proper quench? It's not voodoo or anything else, it's pretty much a basic fact. You can get your quench large enough that it doesn't matter anymore (motor becomes a "non-quench" design - you have to be over 0.1 or so for this to work - some of the Dodge Magnum motors are like this) - but ideally I would build a normal quench motor - and all the values here are in that range anyway.
A larger quench doesn't mean you will blow up right away, but it will hurt your octane tolerance - you may improve it (octane tolerance) by reducing compression, but you will hurt it with a larger quench - so in the end it may be a wash - you could have made more power at the same octane level with a smaller quench/higher compression.
The best bet is to set your compression with the heads/pistons, and keep your quench between 0.035-0.040 or 0.045 or so.
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Joined: Apr 2002
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From: Austin, TX
What chris said, but here is a bit of info that I found that helps explain it further.
Here is my question, Does a typical dished piston impact the squish area (or is the volume all taken out within the chamber area. Even so, it would impact the turbulence, right?
The portion of the head's deck that is outside the combustion chamber but exposed to the bore is used as a squish region. Its function is to create internal charge acceleration that stimulates the end gas and increases the burn velocity as it rushes to escape this area as the piston sweeps toward TDC. It is considered internal charge acceleration because it's created in the bore.
I think the quench is only on a portion of the top of the piston..see the head bowl and youll see the flat part...most dished pistons ar set to press the quench are and dished on the other 2/3rd or so. Could be right...could be wrong...may just not have explained it well as i see it.
