Blueprint specs.

Greg Reimer 7376 · 09-18-2016, 08:11 PM

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.

09-18-2016, 08:11 PM	#4
Greg Reimer 7376 VIP Member Join Date: Nov 2008 Location: Glendora,Calif. Posts: 1,136 Likes: 172 Liked 705 Times in 219 Posts	Re: Blueprint specs. 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.