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I just detonated a piston so I am trying to get my combo correct this time. I think it was the perfect combo just enough blow a hole in #7 piston (to much timing ,motor was hot @210 deg , changed shift points and forgot to change rev limiter)any way this gives me the chance to get it right , but of course I have a budget
as I keep researching I keep coming up with different dynamic calcs . I think my setup is very borderline to the high side because of my cam / head choice . I have dcr calcs from 8.77-9.47
my setup is as follows :
lq4 6.0l 4.00 bore x 3.66 stroke
stock 6.57 dish pistons w/reliefs
head gasket is gm mls 4.06 bore .53 thickness
prc stage 2.5 5.3l heads milled .020 (62cc chambers)
The car ran a strong 12.02 @ 113 mph but I was getting kr from 2nd gear on my afr was a steady 12.5 so I tried backing 2 deg out and up the shift points at the same time . I didn't even realize it burnt a piston and made another 12.19 @ 113 on 7 cyl's
The reason for me asking is I can make a piston change to lower or raise compression or stay with what I have without hurting my budget to much
don't get me wrong I would love to go to a 408 stroker kit , but I am thinking that would require new heads and different cam and that isn't in the budget right now
I got 8.72 with my calc. Would be nice if you could run a thinner gasket like a .040" and get more squish (quench). I think that would be about a 8.96 kind of near the edge although DCR is really very complicated and numbers are only part of the real world results. A tighter squish fights detonation in itself. One thing you could do is get your injectors flow tested and put the highest flow one on #7.
Thanks I figured out what I was doing wrong I was using duration @.050 , now I am down to 8.24 . if I use mahle forged pistons with a +4 cc dish I get 8.48 do you guys think I should tighten up quench ? right now it is .047
If I do a .040 gasket I end up @ 8.77 and a quench of .034 or is that pushing it for 93 octane ?
I don't want to end up with a kr bomb on my hand
and I will while I have everything apart send my injectors out ...thanks
Thanks I figured out what I was doing wrong I was using duration @.050 , now I am down to 8.24 . if I use mahle forged pistons with a +4 cc dish I get 8.48 do you guys think I should tighten up quench ? right now it is .047 If I do a .040 gasket I end up @ 8.77 and a quench of .034 or is that pushing it for 93 octane ? I don't want to end up with a kr bomb on my hand and I will while I have everything apart send my injectors out ...thanks
That's great for 93 octane. .040 HG and .034 quench. Tighter quench helps reduce knocking, so you get a win/win there
That's great for 93 octane. .040 HG and .034 quench. Tighter quench helps reduce knocking, so you get a win/win there
Iron block application; I'm not so sure he should run it quite that tight. Aluminum different story as the deck grows north by 6-8 thousandths or so
In his situation I'd prolly go .045 gasket and be happy medium/safe on the quench.
Just double checking your IVC, here are the numbers on your cams advertised or .006" duration:
When doing compression for these engines, I like to work backward from the known combos as a double check. With that said, here are the numbers with your cam on a stock LQ4:
I am not sure if you are saying that you had 62cc combustion chambers and then milled them .020" or if you are saying you have 62cc combustion chambers after milling the heads. Here are the numbers using a 62 CC combustion chamber and everything else the same:
In looking at these numbers, you are in good shape. If you busted a piston with detonation, it was tune related or you were getting oil in the combustion chamber.
Just double checking your IVC, here are the numbers on your cams advertised or .006" duration:
When doing compression for these engines, I like to work backward from the known combos as a double check. With that said, here are the numbers with your cam on a stock LQ4:
I am not sure if you are saying that you had 62cc combustion chambers and then milled them .020" or if you are saying you have 62cc combustion chambers after milling the heads. Here are the numbers using a 62 CC combustion chamber and everything else the same:
In looking at these numbers, you are in good shape. If you busted a piston with detonation, it was tune related or you were getting oil in the combustion chamber.
they were 65cc heads milled .020, texas speed originally told me they would be 62 cc .
11-08-2015, 08:44 AM
SCR/DCR what is correct calcs ? what am i missing 
