02RedHawk

iTrader: (17)

I was having this discussion with a friend over the weekend, and we came to a subject where we didn't think anything was substantiated (yet).

Will an aftermarket head, ie AFR ETP or others, support a higher DCR than an as-cast GM 243 LS6 head? (Using the 243 head because it presumably has the best chamber design of the LS1/2/6 heads) Are the combustion chambers in the aftermarket heads that superior to the 243 casting - and do the combustion chambers then allow the aftermarket heads like AFR & ETP to support a greater dynamic compression ratio (knock-free) than the *exact* same setup with GM-243 heads?

(For the sake of discussion, we were presuming the car would also already have a well-flowing exhaust (longtube headers) and some sort of upgraded intake, like a ported LS6, FAST, etc.)

So, take two engines (or use the same engine and repeat the experiment, doesn't matter), set them up identically (same cam, same intake, same exhaust, etc.), but on one engine install AFR205s (or ETPs, whatever) milled to 64.67cc, and on the other engine install GM-243's unmilled at 64.67cc. Use the same head-gasket, etc., so that the DCR and SCRs are identical. If the timing were also identical between the two - and the 243-engine had "X" degrees of KR, would you assume the AFR-engine to have A) More KR, B) Less KR, or C) Same KR....?

The question: All else being EQUAL, will the aftermarket heads suppress detonation to a higher DCR than 243 heads?

What if the 243 heads were ported vs. unported (but the combustion chamber untouched)? Any change in your answers?

Patrick G

iTrader: (14)

With the AFRs, the answer is yes. The dual quench pad combustion chamber is a step above the best cathedral port factory casting (241,243,317). So yes, you will get a faster burn and yes, you will be able to handle increased dynamic compression.

Take my setup for example: I have around 11.50:1 static compression and 8.73:1 dynamic compression. I run 26 degrees of timing at peak torque and 30 degrees of timing at higher rpm. Zero knock, even in the Texas heat. This would be hard to do with a factory casting.

Phil99vette

iTrader: (11)

We finally calculated our DCR/SCR and its well above 12.0:1 and about 9.45:1 SCR. 93 octane, 26-27 degrees and no knock.

02RedHawk

iTrader: (17)

Yep, that's what I was figuring.

PatrickG - This with a 160 tstat?

Phil99 - That DCR (9.45) seems awfully high. Can you share your calcs?

Patrick G

iTrader: (14)

Yes, when running a 160 stat, my coolant temps hover around 180-190f with the ac blasting, and 175-180 without. Getting cool air in through the sealed Ram Air hood also helps.

Louie83

iTrader: (3)

I personally don't understand 160 stats. Isn't the optimal engine temperature higher than 180 degrees for running an LS1?

Patrick G

iTrader: (14)

Ideally, you want the block as hot as possible and the cylinder head as cold as possible. With engine temps around 180, the 160 stat seems to strike a happy medium with the hot/cold thing.

Phil99vette

iTrader: (11)

Sure:
3.62 stroke
3.905 bore
-2cc reliefs
52cc heads <== not mistyped
3.910 x .045 gasket
.007 out of hole

254/260 111 +0

Let me find the valve timing @ .006, its written down somewhere here. If memory serves me correctly my SCR is around 12.5:1
Phil

redfirebird

Phil i would be interested in the intake if its still available 4236677356 Dic Davenport

S10xGN

iTrader: (11)

Dude, this thread is 5 years old! Do you really think he still has it?

blk~2000~Z28

yes b/c it is listed in his SIG. I just don't think he knows how to use the PM service or a forum for that matter.