340 High Compression Pistons

340 High Compression Pistons

1badcolt, the question of how much compression you can run has a lot to do with the cam.... which has to do with the use. Can you give us more detail on what you will be doing with the engine/car? Is the cam selected?

IIRC, those recesses milled in the Edelbrock heads are listed as .060" deep. The volume in the very short cylinder shape of that milled recess is about 13 cc's so that leaves 52 cc's in the part of the 60179 Edelbrock chamber above the milled recess. (You could CC that part of the chamber to verify; I would.)

Let's see what can be done with a flat top.

Let's make it easy by starting with a thin Cometic head gasket at .027" thick, which is the minimum they list in their catalog for the MLS types. (Warning: I can't recall if the Edelbrocks have a surface finish proper for the Cometics MLS...needs answering.)
So we can compute this like a closed chamber head with a 52 cc volume, with a 'head gasket' of .087" thick. (.060" in the milled head recess + .027" actual gasket)
And let's further say that the Piston CH height is set as part of the custom setup and the decking and the rod and stroke to push the piston up about .035" from the bottom of the open chamber part of the head. That will give you quench effect.... that = good for high compression. The flat top of the piston would be .087 - .035 = .052" above deck.
Stroke is the stock 3.31" with a 4.08" bore.
Assume a head gasket bore diameter of 4.125" to keep the crevice down the side as tight as practical. (IIRC, that is a standard bore size number from Cometic. 4.100" would be even tighter.)
There is still a crevice between the piston top and sides of the milled recess. I don't know the exact diameter for that recess, but have assumed it is 4.140". A measurement of the diameter of that recess would be helpful.
Finally, let use the fairly typical 5 cc eyebrows. (Dunno what those you show actually are.)

Well, lookit that..... 11.92:1 SCR for those conditions.

Now whether the crevice down the side of the piston in the head and gasket is any issue, I don't know. Maybe others can comment. But it is gonna be a pretty small volume, around 1/3 to 1/2 of a cc unless that milled recess is a really huge diameter... and it is extremely short and < 1/2 of the approximately 1 cc volume of the tall crevice down to the top ring between the side of the piston and the cylinder wall. (Did I ask you measure that recess diameter yet?)

The CH of such a flat top piston will depend on the deck height. If you milled so that the deck is 9.585", then the CH needed to put the flat top of the piston .052" above deck is (9.585 + .052) - (3.31/2 + 6.123) = 1.859".

Note that this is working for a flat top BECAUSE of that milled recess. It makes things so you can pop the piston up above deck a considerable distance, and take advantage of that small 52 cc volume in the chamber above the milled recess. This may be of interest to moparodbuster as he sorts things out.