Pistons down hole

[Nick payne]

It would take a -60cc dish to achieve the cr I'm looking for due to my heads being a 30cc combustion chamber. I looked at that option but was told the piston would be very weak and subject to cracking around the wrist pins. My next step was to change heads all together. The heads I have are really nice heads and flow very good compared to all the other sbf heads I've seen that are similar without spending 10k on a set. Then I was told by the machine shop working on my block that we can run them in the hole. That's when i was made aware of the experience on this site. I really appreciate all the input wether it's what I want to hear or not. I would rather spend the money once even if it costs more.

[piston guy]

I don't have any experience running a piston down in the bore like that but I would still think you would be better off adjusting your displaced volume with piston dish or combustion chamber then running the Piston down like that. I realize in some cases it's the only way you can get the compression low enough

As the engines grow in cubic inches and the heads stay small with the boost rising , keeping compression low is a challenge for sure. Thankfully many are going to alcohol or the super high end race gas and more compression. Steel rings help to keep it all sealed up. "Down in the hole" is a last resort in my opinion as well. "To me" a dish focuses the energy in the center of the piston where it should be. Energy is lost as it spreads sideways.

[4vpc]

How about using the Cometic .140 MLS gasket? I'm thinking about doing that going boosted as my flat top pistons are at zero and I'd rather shell out $400 on gaskets than $700+ on new pistons alone.

Only a suggestion, I have no experience using them. I know about shims but then you have two gaskets each side instead of one thick.

It's a bit redneck, but you can mill or turn .040 from the top of a piston if it's over specified or strong enough to begin with, or even machine a slight dish in it.

[Monza355]

A friend of mine once ran a 427 bbc with 454 dome pistons and nitrous in a 3700 lbs firebird street car.. it ran mid tens with a .092 jet or so in the plate system

[kimosabi]

How about using the Cometic .140 MLS gasket? I'm thinking about doing that going boosted as my flat top pistons are at zero and I'd rather shell out $400 on gaskets than $700+ on new pistons alone.

Only a suggestion, I have no experience using them. I know about shims but then you have two gaskets each side instead of one thick.

It's a bit redneck, but you can mill or turn .040 from the top of a piston if it's over specified or strong enough to begin with, or even machine a slight dish in it.

Gonna have to check with Mahle on that, I doubt they will say anything other than "buy a dished piston" though.

[Dan Timberlake]

225 slant sixes ran their pistons "down the hole."
My recollection is it looked like a mile, but the first online source I stumbled on said 0.140"

[Racerrick]

In 400m ford, the piston is around .08 down and the 351/400 heads have no quench area at all. They run really nice on propane.

[4vpc]

How about using the Cometic .140 MLS gasket? I'm thinking about doing that going boosted as my flat top pistons are at zero and I'd rather shell out $400 on gaskets than $700+ on new pistons alone.

Only a suggestion, I have no experience using them. I know about shims but then you have two gaskets each side instead of one thick.

It's a bit redneck, but you can mill or turn .040 from the top of a piston if it's over specified or strong enough to begin with, or even machine a slight dish in it.

Gonna have to check with Mahle on that, I doubt they will say anything other than "buy a dished piston" though.

Yeah I think so, you need to ask anyone but them.
Of course it is 'application dependent', we did do it on some forged, 1/2hrs work for anyone with a 4 jaw in the lathe. Turbod it put out 125bhp per cylinder and is still running fine some years on. They were pretty heavy things to start of with though.