please check my math!

[stroker mike]

Before I order any parts I want to make sure I got this right...
4.28 bore, 3.38 stroke, 84cc chamber, .038 gasket, piston is a kb162 ( +5cc), .005 in the hole, should turn out to be 9.2:1 with an .044 quench. Am I right?
I wanna get it perfect this time...
The stealth heads and XE275HL cam with an rpm intake and Maddog headers... Should be on target for that 425 hp mark, maybe a little more...?

 

[moper]

Not sure which calculator you're using. I come out with 8.99:1. If it was me, I'd have the pistons brought out proud of the deck by .005" bringing quench to .034" and the heads milled to reduce the chamber size to 74ccs. That gives you a true 10.1:1. Or, you can run the KB400 with it's dome and get 10.25:1 with the piston .005 out of the deck and 84cc heads. The smaller chamber/flat top will make more power but the 84cc/domed deal will be cheaper. Also, which heads? Angle plug heads (RPMs, Indys) need the flat top. Stealths or MP/Edelbrocks/452s it doesnt matter.

 

[stroker mike]

It was recommended to me to keep it below 9.5, with 10:1 am I gonna have any issues? what are the potential issues for a pump gas, frequently driven car?

 

[1wild&crazyguy]

You can do 10.1 with the right cam selection, and further tuning.

 

[dusterdon]

With alloy heads you can probably go to 11:1 and be ok if you have a big enough cam.

 

[moper]

9.5 in aluminum is the same as 8.5 in iron. You can go as high as 10.8 with no issues. When you factor in the cam and a modern build witha tight quench, you can go up past 11:1 with ease. It's just not easy to get compression in a 383 because of the piston choice. You can spend to mill heads or block, or pay to get custom pistons. The pistons are usually cheaper and you can get a better result using them.

 

[Babyblue66]

Agreed, 9.2 is fine for iron heads, but aluminum can be a point higher, no problem with good quench.