35 thou is the minimum, meaning that if it's off by just a couple of thou the piston might meet the head with "extreme predjudice". For example, what if the deck isn't completely parallel to the main bore? Or a piston could have a little too much side clearance and rock in the bore. Or one rod is a bit too long, etc. IOW, 35 thou must be the minimum on all eight, the pistons all have have the correct clearance, you need to measure all the rods center to center and meaure all the pistons, etc.

That's why production motors aren't anywhere near 35 thou. Too much chance of an error with production line variability.

As far as gasket choices go, I am not familiar with every LT1 gasket, but I know the stock gasket is thicker than the FP #1074, for example.

Rich

Rich

 

I've used quench as tight as .028 without a problem. Not exactly by choice but never any contact. That was a low-rpm race engine (7800 rpm, steel rod) which still had adequate piston-to-valve clearance. The valve clearance is the real stickler IMO. So is the growth of the piston above the pin. Some grow more than others.

Based on my experiences, I never sweat .035 minimum, and try to shoot for .035-.045.

I would also opt for a comp height that allows for decking the block. The decks squareness leaves something to be desired on most sbc blocks.

-Mindgame

 

Along the lines of what MG stated, I consider .025" a bare minimum for a quench hgt. This however, leaves assembler with zero tolerance for errors and variations among the four corners of the block, rods or crank throw tolerances. I feel confortable with .030-.035".

You don't wait to purchase the pistons. Although piston deck hgt. dimension, like wall clearance spec, is usually designed into the piston, I prefer to machine around what you intend to use. Crunch the numbers for the parts used, to determine what is needed in the way of machined dimensions. A good shop prefers to be informed what the compressin hgt. of the piston is, the clearance you want, and they will deck accordingly. Some shops prefer not to go beyond the 9.025" dimension unless you can show them you now what you are doing. The oem block will in most cases, not be premachined to the std. 9.025". Most producton oem blocks have enuf extra stock on them to allow correction of the 'kitty whompus' oem machining and still allow ample room to maintain the std. 9.025" block hgt.

With a .039" gasket, I feel comfortable with piston sticking out of the hole, as with the oem LSx engines, although the last engine was machined to std. deck hgt. dimension of 9.025. This resulted in the gasket thickness being the actual quench hgt.

 

.038 IMO is the least you should have for a 4340 steel rod motor on the street.Racing trailer queen,different story.

 

You can't ignore Arnie's statement about "zero tolerance" for error. There's a big difference between a very carefully constructed race motor and your typical performance buildup. The race engine is going to use some tricks and techniques that are very cost/time ineffective for a street motor just to gain a few hp. Pros need those extra couple of hp as they may be the difference between the winners circle or the trailer. Even if you aren't a pro, if you are building your own motor there's still the pride factor. And in that case, the cost is "just" your time. And since it's a hobby, the time spent is actually enjoyable. It's fun to assemble a motor as meticulously as you can using every trick you can think of. My personal favorite is just getting everything "surgically clean". No real benefit to it, I just like cleaning stuff! Problem is, on at least one occasion I really didn't want to run the thing, it looked so nice. That was a motorcycle many years ago. But I still have it even though I don't ride anymore.

Rich

 

I'll bet you do, Doc.

From personal observation, folks who "scrub" before going to work tend to be really neat and clean in most every thing they do.

 

My workbench is cleaner than my desk

Rich