I've got a few questions about some of the specs of a typical small block (305 and 350) that you'd find in a thirdgen.

First, the pistons have 4 small valve reliefs, correct? Does anybody know what that total volume is?

Second, what is the depth of the piston, as measured from the block deck down to the piston top? (the "in the hole" depth)

Third, what kind of compression ratio do you typically get when you put a 64 cc head on a 350 engine?

I've been putting numbers into desktop dyno for compression calculations, and it would be nice to know what some of those measurements are.


Thanks!

 

As long as you're not terribly worried about accuracy (which you probably aren't if you're using desktop dyno ), take the stock CR with the stock chamber size for your engine and work backwards to figure out what it would be with the smaller chambers.

 

Typical 4 valve reliefs are 6cc but that may be for only 2 valve reliefs. Piston depth can be just about anything. Typical factory piston depth is around .030".

64cc heads and flat top piston in a 350 make 10.3:1 compression ratio.

There are too many factors to determine an exact number. How much area is inside the head gasket hole. It's not the exact same size as a cylinder. How much area is around the piston down to the first compression ring is also part of the cylinder volume. If you really want to get picky. How much area is lost in the combustion chamber from the spark plug protruding into the cylinder.

 

That was roughly in line with my estimate and from a few articles I've read; so with the valve reliefs and depending on head gasket thickness, the ratio for 64cc's on a 350 would be from about 9.5-10 to one, right?

I have tried the working backwards approach, by setting up the parameters to get a given ratio, then changing only the head chamber cc. It looks like there's about half a point difference going from 64 to 58, if I remember right.



In case you were wondering, I've been looking at Sportsman IIs, 200cc intake w/ 64 cc chambers, possibly used in a combo with a Magnum 270H cam and Victor Junior intake