Blueprint specs.

[Michael K]

Question about deck clearance given in the NHRA blueprint specs - does the clearance include the head gasket thickness listed?

[Todd Gross]

No sir. The deck clearance is just that. The head gasket thickness is specified separately.
If your piston/deck is to shallow or wide, you are allowed to alter the Spec gasket thickness to make up the difference.
Reference NHRA rule book section 10A, Pg4 under gaskets for Stock and section 11A page 3 for Super Stock.
Hope this helps.



Todd Gross


= Journeyman=____
Performance Engines Inc.

[Michael K]

Thanks.

[Greg Reimer 7376]

Where head gaskets are concerned(obviously that's what we're discussing here,since it's about deck height),you need to determine what the minimum total deck height with gasket you need to establish proper clearance between the top the piston and the bottom of the head at the top of each gear plus a few. Determine what head gasket you want to use, measure it, then you know how much deck height you have to have above the piston at TDC. It's usually more than the spec. You need a few thousandths more than the minimum because as a rod stretches at high RPM's on the exhaust stroke,you don't want the area of the piston above the top ring to contact the head. That could pinch the top ring in its land causing a total lack of ring seal, a broken ring, a scored cylinder wall, and that's for starters.The NHRA spec is pretty immaterial at this point, just be sure you have more deck height than the spec calls for. Too much deck height can be compensated for with a thinner gasket,just don't make it too thin for all the above mentioned reasons. I built a 327 about 20 years ago in the days of cast pistons and OEM rods, and had .030"deck on 6 cylinders,.028" on one, and .026" on the last one.After that engine had been used for some time, it came down for one reason or another, and I found the faintest imprint of carbon on the .026"down piston in the shape of the outline of the combustion chamber on the flat part of the piston. It ran a max RPM of about 6800rpm. That rod stretched all of that .026" in order to touch that lightly. .022-.025"could have done damage. There's nothing trying to stop the piston at TDC on the exhaust stroke but the two rod bolts, and the beam section of the rod and the bolts absorb all that stretch force. It's absolutely amazing that engines lasted as long as they did. Better materials have sure helped engine longevity,that's for sure.

[Mike Taylor 3601]

deck clearance can be changed from spec, IE spec shows .025'' deck clearance and .016'' thick gasket, which would be a total of .041''. so as a example you could change to .002 deck clearance and .039'' thick gasket and be .041''
As long as distance between piston and head = the spec for deck clearance and gasket thickness combined is legal,always allow .002-.003'' extra to make sure you stay on the legal side.

Mike Taylor 3601

[Greg Reimer 7376]

My 327 calls for .002" tech height and a gasket thickness of .018" for a total deck with gasket of .020". We all know you would NEVER set an engine up that close. It would'nt work over 3000 rpm without clearance issues.This is nothing but a legal minimum. It's OK to have more deck height and gasket thickness than the minimum. Long ago, I built a 283 with a standard bore used block(try finding one now),and after getting the block and the assembly back from the machine shop, I trial assembled it without rings just to see what we had.We had .050"on one bank, .038"on the other, and that was without gaskets. I never remember hearing of the tech team measuring anybody's gasket thickness in a tear down situation. Anybody have their deck height checked,either?