Trouble finding thin head gaskets?
Race Director
Joined: Apr 2003
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From: Tampa, Florida
Jim, any chance you still have the link to the Speedtalk thread on the subject? Because that's really interesting and kinda blows my mind. I can't understand why the thinner gasket would be preferred other than the fact that the gasket's inside diameter is often way larger than the actual bore size...
Vizard had a good rule-of-thumb on how much power increase you get from a decreasing quench (assuming due to a faster burn); but I didn't save it....
If I remember right the "ideal" / "safe" piston to head clearance is also based upon the rod and rod bolt that you have and the RPM that you plan to spin, right? (Lower RPM with less stretchable rod materials / designs can safely have tighter piston to head clearances)
Adam
Vizard had a good rule-of-thumb on how much power increase you get from a decreasing quench (assuming due to a faster burn); but I didn't save it....
If I remember right the "ideal" / "safe" piston to head clearance is also based upon the rod and rod bolt that you have and the RPM that you plan to spin, right? (Lower RPM with less stretchable rod materials / designs can safely have tighter piston to head clearances)
Adam
Ideal/safe is also based on 'stacking' of clearances, .001 here, .002 there, crank flex, etc. Then there's thermal expansion which is independent of RPM...
Melting Slicks
Joined: Jun 2016
Posts: 2,979
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From: Woodinville WA
I don't have a particular link but those guys weren't overly particular about it either. It was more of a '30, 40, 50' whatever, don't worry about it. Optimize everything else first then worry about quench. Keep in mind that AFR recommends Felpro 1003 with their heads which is an .041 gasket. With a zero deck you're starting at .041 quench!! GM quench's are all higher than that!!
Ideal/safe is also based on 'stacking' of clearances, .001 here, .002 there, crank flex, etc. Then there's thermal expansion which is independent of RPM...
Ideal/safe is also based on 'stacking' of clearances, .001 here, .002 there, crank flex, etc. Then there's thermal expansion which is independent of RPM...
(After comparing my Profiler heads' passages vs. the Felpro 1094 gasket, I kinda wish they had worked with FelPro on the gasket. Some pretty huge differences...)
Adam
Adam
Last edited by NewbVetteGuy; Oct 8, 2018 at 04:57 PM.
Race Director
Joined: Mar 2018
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From: Golden Colorado
Not enough..................
I don't have a particular link but those guys weren't overly particular about it either. It was more of a '30, 40, 50' whatever, don't worry about it. Optimize everything else first then worry about quench. Keep in mind that AFR recommends Felpro 1003 with their heads which is an .041 gasket. With a zero deck you're starting at .041 quench!! GM quench's are all higher than that!!
Ideal/safe is also based on 'stacking' of clearances, .001 here, .002 there, crank flex, etc. Then there's thermal expansion which is independent of RPM...
Ideal/safe is also based on 'stacking' of clearances, .001 here, .002 there, crank flex, etc. Then there's thermal expansion which is independent of RPM...
Thanks
Racer
Joined: Jan 2008
Posts: 295
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From: Arvada Colorado
Race Director
Joined: Mar 2018
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From: Golden Colorado
Great article.................
Here, read this article: http://www.superchevy.com/how-to/eng...earance-guide/
Melting Slicks
Joined: Jun 2016
Posts: 2,979
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From: Woodinville WA
Thanks - very interesting article. Now I'm really thinking, I used the 049 head and it has a pretty steep angle mill cut. Forged pistons so I am sure the machinist put some room in there and there in lies my concern, piston rock at TDC bumping the piston into the head. The engine is all together and in the car so the dilemma becomes whether to run it or take it back out and pull the heads for fatter head gaskets. Assuming the "zero deck" gives up .005" or so it looks like I am still way under the recommended minimum!!! Thanks again. Good article.
Race Director
Joined: Mar 2018
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From: Golden Colorado
I did a search for "bbc minimum quench" and got about 460some hits. After lots of reading, some of it from some pretty big names in engine building, the general consensus is bbc steel rods, forged pistons with around .008 clearance, .0025 rod bearing, thermal expansion for rod, and about .005 to .007 "piston rock" at TDC - minimum quench, there should be .035 to .040 (on the tight side) for 6500 rpm. So..............looks like I need to pull the heads and put some thicker head gaskets in and just live with the slight decrease in compression. Oh well better to error on the side of caution.
Race Director
Joined: Apr 2003
Posts: 19,352
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From: Tampa, Florida
Adam, I was mistaken, it was a YB thread...with street engines it may make no difference
Post 54 lays it out...but read entire thread!!!
https://www.yellowbullet.com/forum/s....php?t=2530687
Post 54 lays it out...but read entire thread!!!
You want to keep the piston in the hole and run a thinner gasket. Your bore size is always smaller in diameter than what your gasket is. So that means less volume in the chamber area which means more compression. Now depending on which SS class you run might depend on the rule you have to follow. Let me know and I can try and help more...
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This is a 6 inch rod two valve relief forged Weisco 7 cc piston. Block was blue printed with a slight decking. So the pistons are .020 down in the hole. That is why I have tried to always use about .020 gaskets to get .040 quench. This particular motor ends up with about 10.86 C/R and it has a 7500 rpm rev limiter. To get the dyno simulator software programs to reach a mid 500 hp goal it required the head flow of AFR 210 or 227 cc heads, team "G" single plane and 1 3/4 headers into a free flowing 3 inch exhaust.