zero deck height or thinner head gasket?
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From: hamilton waikato
zero deck height or thinner head gasket?
im planning a rebuild of my stock 350 and having learnt about the benifits of quench from this site would like to maximise it.
what are the pros and cons of thinner head gaskets vs a zero deck height?
cheers
what are the pros and cons of thinner head gaskets vs a zero deck height?
cheers
Safety Car
Joined: Sep 2001
Posts: 4,154
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From: Glenbeulah Wi
Either way will work but if your deck surface is flat and a thinner head gasket will work then it will save you money to use the thinner gasket. The thinner gasket also saves the block for more rebuilds in the future.
Also the tighter quench (.040) does not raise your octane requirement it actually lower it because it decreases the onset of detonation by increasing turbulance in the cylinder (mixing). Once the quench exceeds .050, quench has almost no effect on detonation and you run the risk of having detonation.
A typical SBC with stock decks leaves the piston .025 in the hole, with a fel-pro 1094 gasket (.015) you end up with .040 total pistin to head clearance or quench. If this works out it can save you money over machining the block.
Also the tighter quench (.040) does not raise your octane requirement it actually lower it because it decreases the onset of detonation by increasing turbulance in the cylinder (mixing). Once the quench exceeds .050, quench has almost no effect on detonation and you run the risk of having detonation.
A typical SBC with stock decks leaves the piston .025 in the hole, with a fel-pro 1094 gasket (.015) you end up with .040 total pistin to head clearance or quench. If this works out it can save you money over machining the block.
Le Mans Master
Joined: Aug 2010
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Either way will work but if your deck surface is flat and a thinner head gasket will work then it will save you money to use the thinner gasket. The thinner gasket also saves the block for more rebuilds in the future.
Also the tighter quench (.040) does not raise your octane requirement it actually lower it because it decreases the onset of detonation by increasing turbulance in the cylinder (mixing). Once the quench exceeds .050, quench has almost no effect on detonation and you run the risk of having detonation.
A typical SBC with stock decks leaves the piston .025 in the hole, with a fel-pro 1094 gasket (.015) you end up with .040 total pistin to head clearance or quench. If this works out it can save you money over machining the block.
Also the tighter quench (.040) does not raise your octane requirement it actually lower it because it decreases the onset of detonation by increasing turbulance in the cylinder (mixing). Once the quench exceeds .050, quench has almost no effect on detonation and you run the risk of having detonation.
A typical SBC with stock decks leaves the piston .025 in the hole, with a fel-pro 1094 gasket (.015) you end up with .040 total pistin to head clearance or quench. If this works out it can save you money over machining the block.
Le Mans Master
Joined: Mar 2002
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From: Castro Valley Calif.
St. Jude Donor '03 thru '26
Either way will work but if your deck surface is flat and a thinner head gasket will work then it will save you money to use the thinner gasket. The thinner gasket also saves the block for more rebuilds in the future.
Also the tighter quench (.040) does not raise your octane requirement it actually lower it because it decreases the onset of detonation by increasing turbulance in the cylinder (mixing). Once the quench exceeds .050, quench has almost no effect on detonation and you run the risk of having detonation.
A typical SBC with stock decks leaves the piston .025 in the hole, with a fel-pro 1094 gasket (.015) you end up with .040 total pistin to head clearance or quench. If this works out it can save you money over machining the block.
Also the tighter quench (.040) does not raise your octane requirement it actually lower it because it decreases the onset of detonation by increasing turbulance in the cylinder (mixing). Once the quench exceeds .050, quench has almost no effect on detonation and you run the risk of having detonation.
A typical SBC with stock decks leaves the piston .025 in the hole, with a fel-pro 1094 gasket (.015) you end up with .040 total pistin to head clearance or quench. If this works out it can save you money over machining the block.
Don't forget to ensure valve lift & piston reliefs work together & finally, check your P-V clearances with clay. P-V clearance is normally affected by cam timing and duration in addition to the quench.
Melting Slicks
Joined: Jan 2009
Posts: 3,482
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From: folsom california
for quench to happen, the piston must be a flat top; at least in the "quench" area in the head. some are. some aren't. choose carefully.
as important as head gasket thickness may be, even more important is that the type of gasket you choose be compatible with the material the head is made of, which I assume is aluminum, and the cast iron block and that the heads be finished to the appropriate smoothness. Back when heads and blocks were both cast iron this wasn't such an issue, but it is now.
as important as head gasket thickness may be, even more important is that the type of gasket you choose be compatible with the material the head is made of, which I assume is aluminum, and the cast iron block and that the heads be finished to the appropriate smoothness. Back when heads and blocks were both cast iron this wasn't such an issue, but it is now.
Race Director
Joined: Nov 2003
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
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I agree with Brian.
I was also under the impression that inverted dome pistons were the best for quench -- as the point of the issue is to squeeze the flameball into a tighter "sphere". As such, time for ignition decreases since you're igniting a smaller ball of fuel. Having a shorter "flamefront" means less ignition timing is necessary.
Other shapes of pistons work as well...the main idea is to squeeze the charge inward and avoid hot-spots of detonation. Though I read about this on Silvolite's website, there is a very good thread on the subject in this tech forum.
I think the other issue the OP is asking is how much does it affect quench to leave the piston .025 down in the hole vs zero-decking it. Ideally, I think you want to get combustion up into the head chamber but it's not critical to gain some/most of the benefits. At least part of the reason for this is you get better flow thru the cylinder heads when part of the charge isn't sitting down in a hole -- probably the most important during the scavenging process.
I was also under the impression that inverted dome pistons were the best for quench -- as the point of the issue is to squeeze the flameball into a tighter "sphere". As such, time for ignition decreases since you're igniting a smaller ball of fuel. Having a shorter "flamefront" means less ignition timing is necessary.
Other shapes of pistons work as well...the main idea is to squeeze the charge inward and avoid hot-spots of detonation. Though I read about this on Silvolite's website, there is a very good thread on the subject in this tech forum.
I think the other issue the OP is asking is how much does it affect quench to leave the piston .025 down in the hole vs zero-decking it. Ideally, I think you want to get combustion up into the head chamber but it's not critical to gain some/most of the benefits. At least part of the reason for this is you get better flow thru the cylinder heads when part of the charge isn't sitting down in a hole -- probably the most important during the scavenging process.
Last edited by GREGGPENN; Mar 9, 2012 at 05:50 PM. Reason: Added last sentence.
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From: Dale City VA
It dosen't matter how you get your target quench. .040 piston to head is .040 piston to head.....
The main advantage to running the piston in the hole and using a thin gasket is you have a thicker/stronger deck surface on the block.
1) Decide what you wanto to target your quench distance at.
2) Look over your head gasket options.
3) Select the combination of machine work and parts that suites your quench goal.
BTW you can run way tighter than .040 quench in a fairly low RPM engine with tight piston to wall clearances.... or in higher RPM motor if you have a really good rotating assy.
I'm running .034 quench, turning over 7000RPM in my 92.
Will
The main advantage to running the piston in the hole and using a thin gasket is you have a thicker/stronger deck surface on the block.
1) Decide what you wanto to target your quench distance at.
2) Look over your head gasket options.
3) Select the combination of machine work and parts that suites your quench goal.
BTW you can run way tighter than .040 quench in a fairly low RPM engine with tight piston to wall clearances.... or in higher RPM motor if you have a really good rotating assy.
I'm running .034 quench, turning over 7000RPM in my 92.
Will
