Sorry i know this has been beat to death but i cant seem to find any info on this.

Im currently running a 388 (bored .060 over) and have a bad pinging. I ordered .062 head gaskets but im not sure that it will resovle my problem. The deck height is either .019" or .025" (calulated using specs from piston manufacturer.) my heads are ANGLE MILLED .030" i tried the old trick with the water and found them to be no smaller than 60cc combustion chamber i "think." but I was wondering if there is a math method to figure out exactly how much was taken off cc wise? There was a website that said to use this equation,

old cc's (64cc) - number found = amount milled (.030) / .0065 (number from DART)

using this formula it says that 4cc's were taken off. i understand and angle milling generally doesn't effect the compression as much as straight milling (if thats what its called.)

so are my heads 60cc combustion chamber now? I hope so or otherwise i have to order thicker head gaskets and i want to drive it now!... haha thanks for all the help

 

Doesn't really matter too much what cc's the cylinder heads are. IIRC, you were at 10.9:1 comp ratio last time. Going from a .040 to a .062 thickness is only about a .5 drop in compression ratio, assuming the bore of the gasket remains the same. 10.5ish is still borderline too high for iron heads. I would keep it under 10:1. Especially with minimal quench effect.

But generally, yes, that number (cc's removed) sounds about right, maybe a bit high. Depends on chamber design and specific angle of the mill, though. The only way to determine, with certainty, the cc's of the chamber would be to use a burette and measure it out.

 

not sure on the chamber design kinda looks like a "D" with the curved part holding the valves and the flat part where the plug comes in. But at 10.6:1 on iron heads will it ping like it is now at 11.2:1? i want the compression low enough to run 93 octane without any octane boost or additives. its pinging now but if i advance the timing it will start detonating. i think i might send back the gaskets for the next step larger (.072). but these numbers are also found using 60cc combustion chamber and my buddy and i used a surange to fill the heads and found it to be 62cc. so im using the smaller number just to be on the safe side. all in all i think ill be buying the .072" thick gaskets.

 

Personally, I think it's still high, with a chance of ping. If you were to have a tighter quench, optimal being .042" or so, then I would say it could be done with some trick timing. But you'll have quench around .090" or so, which pretty much negates the effect.

If the cam were large enough, that could also help, but I don't remember the specs...

Also, what pistons are you running? I.e. What's causing your compression to be rather high.

 

im just running forged flat tops w/valve reliefs (-4 relief cc), but with the longer stroke of the the 383 and the heads being milled boosts my compression up a lot. The person before me milled the heads to raise compression. I wasn't sure if it was going to make that much of a difference but i guess it did.

the cam specs are:

lobe seperation is 110*
duration is 240/246 at .005"
lift is .507/.510 (intake/exhaust)

i'm going to get my heads off and double check the combustion chamber size but i think im just a smidge higher than 60cc.

 

TTT