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I posted the 408 motor combination in my 68 valiant race car here last week and through the responses i got, it seems i need to increase compression from 10.8 to 12.5 or 13.1 to reach my goal of 10.00's
The issue i'm having with doing this is how can i get that compression considering the relatively large chamber of the CNC indy head (68-70 cc) My current 408 combo has diamond flat top pistons, set .005 below deck.
I talked to RyanJ about increasing compression, and he suggested we mill the heads down to the intake valve seats, making them 59-60cc's. That will increase compression to 12.3 by my calculations. I guess you could call me a conservative, but i'm worried about doing that since the heads will never be able to be cut again.
How are other 360 head users making this kind of compression? Custom domes? thanks-Andy



there's no doubt that milling the heads is the "cheapest" way, for the time being at least. one of the problems is it doesn't really get you where you want to be on C/R. the other is that your basically to the limit of how much you can mill that head. what happens in the future not if, but when they need to be touched up again? another thing that happens is you affect the amount of valve to piston clearance by milling that much off any head, especially the Indy head though because of the valve/ seat placement in the chamber. you'll also be milling a ton either off the intake side of the head or the intake itself. that can be problematic to take that much off the intake side of the head since that area is already thin. sealing, or even fitting the valve cover can become a problem. as far as i know, everyone that we've done pistons for here on Moparts has been very pleased with what we've done, and that's a lot of people.

Last edited by DRAM_Perf_Only; 09/16/09 10:03 PM.