Seems so, he has been able to find them and when I was looking around I found them also at the time. My opinion is a dish piston is used when you cannot lower the compression any other way

You can alway lose some cc's in the chambers and gain a few ponies at the same time. I'm not familiar with vortec heads but pretty easy to open up 6 plus cc's. I'd cc chambers if their second hand just to be certain.

Can lose another cc with bore notching but that's not much. But sometimes every little bit can help.

Use Wallace racing compression calculator.

Thanks,

When the guy was first looking into the build we were working the numbers and there have been some mis matchs depending on which calculator used. So I work the numbers and came up with these initially.

I did not take into account the gap between the top of the piston down to the first compression ring, but the math worked seemed to work out. This is what was used to formulate the ratio currently.

Just thought a bit after Midvally's post, which made me think the dish is trading one thing for another. Use a 12CC dish and a .025 gasket or use a .040 gasket an flat top, about the same. Like the idea of keeping the piston in the hole a slight bit (.005 or tad more) more then 100% zero deck

It seems he is asking questions after all the machine work has been made completed and parts bought. At this point measure accurately how far the piston is in the hole, calculate the chamber volume needed to achieve 9.4:1 compression ratio and work the head according to chamber size required. He will need +.100 valves and narrow body self aligning roller rockers. What intake and carburetor is he using?

Nothing has been bought yet, his machine shop wants him to use flat top, but he's thinking dish is better.

It will be carb, just sent message as to what carb and intake

I’d tell the machine shop to put the piston .005-.008 in the hole, use a .039 thick head gasket for quench and modify the chamber to produce 9.4:1 compression ratio. Use whatever piston necessary. The worked chambers will help against detonation. If using the stock oil pan do not use high volume pump. What is the application for this engine?

Keep the compression around 9.5:1 for iron head vortec pleasure marine. Pushing it higher will risk issues with pump gas.

yes... victor rinz makes a .022 and .025 shim style stainless gasket

use the flat tops and make sure the chamber is 65-66CC plus approx .050 of quench you will be at 9.55:1 9.6:1 is about max for 87 in a pinch and 89 as majority fuel

dish pistons can create turbulence a flat top wont