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Question my compression ratio for pump gas...

Posted: April 10th, 2012, 1:06 pm
by Dezertxj88
:doh:

Alright guys my blocks machined, my crank is here, my rods & pistons are ready to drop in. Now since I'm here I figured I should just do a cam, but I'm worried if it will run on 91oct. Its a HIGH compression 4.2L, ported head, .038 quench.

9.73SCR, and 8.31DCR.

3.935" piston
3.500 stroke
60cc combustion chambers
12cc dish (2229 pistons)
.043 head gasket
-.005 deck clearance
6.125" rods.

This gives me 9.73:1SCR...adding in the Comp 232 vs the 87-95 OEM cam, my DCR goes from 7.1:1 to 8.3:1...is this still safe on 91oct?

Re: Question my compression ratio for pump gas...

Posted: April 10th, 2012, 2:18 pm
by Muad'Dib
I have almost 8.5 DCR and i only have a slight ping at sea level running premium. I live at about 3500ft though so this is rarely an issue and its nothing Octane Booster doesnt solve.

Every engine is different though.. and with your tighter than tight quench and lower DCR, i am willing to say that you should be OK.

Re: Question my compression ratio for pump gas...

Posted: April 10th, 2012, 4:36 pm
by Dezertxj88
Ok cool..I'm at sea level, it'll be tuned via a SAFC II..also have polished combustion chambers, and am looking at how to polish my top of the pistons tops before it goes together..