[steve25]

Cliff, do you happen to know what this motors cranking compression was?

[Cliff R]

No, since I was only hired to assembly and dyno I didn't check piston dish or combustion chamber volume. I suspect the compression was under 10 to 1 simply because it made less vacuum at idle and needed more timing and idle fuel than any of the ones I've done here. Compression is a key play in making power (torque) with these engines. The camshaft must be chosen according to the CID and compression to make optimum power on pump gas, simple as that. Doesn't mean that you can't make decent power with low compression, but for sure higher compression allows for less negatives with larger cams.......Cliff

[steve25]

One big key part of the puzzle is that below a certain compression ratio a motor needs really good low lift flow to clear our the cylinder!

Since low compression engines have such a slow burn rate they also hold on to more unusable cylinder pressure / gases at BDC and this needs to be gotten rid of at a fast rate before the piston even starts back up the Bore to initiate the Exh cycle!

[Vid]

Well fellas good news, it looks like I lined up a pair of brand new, still in the box completely assembled larger chamber KRE heads that someone fairly local to me had bought but never used for his 455 Firebird project. Very fair and reasonable price of $2k. I pick them up next week.

No worries about dish size now but after absorbing the information in this thread I guess that didn’t matter anyway. Thanks for all of the good info, I learned a lot!

Maybe I’ll even go 4.5” stroke and a roller instead of HFT cam now, haha.

I’ll save my #62 heads for the tired but original 350 I’m pulling out of the Le Mans and use them when I freshen the little motor up.


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[Vengeance Race Engines]

Originally Posted by Vid

Hi all,

Just curious how much dish some of you are running, and what’s the most you’re cutting out? Anybody at or near 30cc?

I’m considering the options on my build and of course a major factor is cubic inches versus combustion chamber size. Still teetering on buying aluminum heads or using my ported 62 iron heads, if I use the iron heads and Butler’s 471 stroker assembly withRoss pistons (400 block .030 over) a 30cc dish calculates out to 9.4:1, which ‘should’ work with 91 pump gas. Butler says 30cc is doable, but pushing it. I don’t know if pushing the envelope is a good thing to do or not in this case? But if it works without issues, I just might. Thanks for any feedback!


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What they mean by "pushing the limits" is you can only remove so much volume in the crown for a specific piston design. Big dish in a smaller diameter with a high pin and ring land leads to trouble. It's not the actual size of a dish being the issue, it just needs to work with the piston design. If it doesn't, it becomes the issue they are referring to.

Originally Posted by 77 TRASHCAN

So Bart, that's leaving you a .035ish quench distance???

Nothing wrong with a real tight quench distance. I have run tighter, but it isn't recommended nor is it commonplace on every engine. Very application specific. However .036" works very well in a lot of applications.

Originally Posted by tom s

I was told by Autotec that a dish can get too big and compromise the integrity of deck.They get around it by what he called a donut but have NO clue what that was.I did a 23cc dish in a 4.04 bore piston.Tom

The "Donut" he was talking about is a full circular dish , but the middle is a raised radius. If you lool at it from the top, it looks like a donut. We use this design quite often in certain applications.