cormyr

with a quench of .064" and a 10.5:1 c/r with aluminum heads, flattop pistons, 180 deg thermo, and a 226/226@.050 cam do you think i will have problems with detonation or should this setup be ok?

ede

ideal quench is around .040, you're way over that. think i'd reduce head gasket thinckness and try to get it down a little. if the block isn't assembled i'd zero deck it. hard to predict if you have detionation or not, but i'd say with right fuel and timing no.

cormyr

ok i guess i need to clarify. obviuously i know that .040 is the ideal quench. dunno if you've looked around but none of the aftermarket companies make a piston that is anywhere between -5cc and -12cc. therefore, i have to deal with a not-so-optimal quench. anyone who has built a 383 f/i street vehicle knows what i am talking about. given that, anyone out there who has done this before with decent results?

ME Leigh

What -5cc and -12cc are the most common pistons. -5cc pistons are flatops with valve reliefs and -12cc are a slight dish.

cormyr

probe industries makes a -12.8cc forged dish. srp makes a -5cc forged flattop. i have yet to find anything in-between.

ME Leigh

Oops sorry i just reread your post and i'm an idiot. If you need to reduce compression alittle i would grind in the combustion chamber. Get a carbid cutter and a diegrinder and unshroud the valves. Just grind off whatever you need 1cc 2cc, 3cc ...

BTW have you cc the heads to find out what they really measure as?

cormyr

yep they came in at 63cc. they are lingenfelter fully cnc'd heads so im not into cuting them up with a die grinder.

i guess my real question is how wide can i go on the quench before it actually presents a problem? i've seen posts with guys running .070+ without problems but at a lower c/r. i was wondering if anyone out there has done this with a higher c/r and aluminum heads.

Streetiron85

I've heard that tightening the quench more than compensates for the increase in CR as far as the octane sensitivity is concerned.
In other words 10.5/1 CR with .070" clearance would supposedly be more detonation prone than 11/1 CR with .040".
That's what some guys say anyhow.
I plan on doing some experiments with that, but haven't had a chance to yet... Sorry
It sounds like a good opportunity for you to do an experiment of your own.
If it pings, it could be an excuse to get a bigger cam.

http://kb-silvolite.com/calc.php?action=comp

The link above is a dynamic CR calculator that might help you to figure it out

cormyr

check this out btw:

https://www.thirdgen.org/techbb2/sho...ghlight=quench

Streetiron85

I couldn't locate this link at first.
There might be some useful info here.
You won't need to do all the math that's detailed on that site since the calculator on the KB site does that for you. But some of the data is still applicable.

http://members.uia.net/pkelley2/DynamicCR.html

And here's a guy who's running flattops with small chamber heads, on his 383. I don't know what he uses for fuel on the street tho

http://www.karl-ellwein.org/383y2001.htm