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60 footing
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Discussion Starter #1
well, i posted this in the MKIV (1993-1998) with no answer, so i'll post it here since this is a drag car

any ways heres my setup
build head with stock valves, 272/272, 1600cc + weldon pump, JE 8.5.1 CR pistons +1.2 comtic HG, GT42-76R, NX kit, AEM
the question is, do you guys think 8.5.1 plus 1.2 gasget is over kill for my setup, i mean very low CR ?
most likly i'll be running 33+ psi and 150 shot on C16

another question, whats the highest boost can i run on the GT42-76R 1.01 A/R and still in the safe side ?

keep in mind this is a drag race car not street car
 

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60 footing
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Discussion Starter #3
non
 

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I run 9.5:1 CR and 41psi and 150shot without issue. If your using ARP L19's and keeping C16 in it, then your compression is too low for optimum power and spool.
 

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60 footing
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Discussion Starter #5
im using the regular ARP head stud i dont know if they the L19 or not, now how could i up my CR, are the OEM head gasget boost/N20 friendly ?
what kinda of solution do i have ?
to much boost and 200 shot plus more timing ?
 

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Vendor
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well, i posted this in the MKIV (1993-1998) with no answer, so i'll post it here since this is a drag car

any ways heres my setup
build head with stock valves, 272/272, 1600cc + weldon pump, JE 8.5.1 CR pistons +1.2 comtic HG, GT42-76R, NX kit, AEM
the question is, do you guys think 8.5.1 plus 1.2 gasget is over kill for my setup, i mean very low CR ?
most likly i'll be running 33+ psi and 150 shot on C16

another question, whats the highest boost can i run on the GT42-76R 1.01 A/R and still in the safe side ?

keep in mind this is a drag race car not street car
You can't just say "JE 8.5:1 CR", you need to use the actual dish of the piston, your specific combusion chamber volume after the headwork, the thickness of your headgasket and of course the cylinder volume and calculate it for your specific engine.
 

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There isn't a whole heck of alot of room to increase combustion chamber volume on the head... They are all valve. There is no reason to do any work on the head there except maybe a little polishing. I don't know how much a 1.2mm gasket lowers compression, but it's obviously thicker than stock, lowering compression below 8.5... Based on what he wants out of the car, I'm saying he needs more compression. I never recommend below 9:1 on anything boosted.
 

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There isn't a whole heck of alot of room to increase combustion chamber volume on the head... They are all valve. There is no reason to do any work on the head there except maybe a little polishing. I don't know how much a 1.2mm gasket lowers compression, but it's obviously thicker than stock, lowering compression below 8.5... Based on what he wants out of the car, I'm saying he needs more compression. I never recommend below 9:1 on anything boosted.

I didn't say he had a BBC, I just said to correctly calculate CR, you actually have to calculate CR...

No more, no less. Pistons are not a specific compression ratio, they have a specific volume, dish, dome, flat, etc.

But yes you can still work the chamber. Honestly if anything I'm agreeing with you, I like compression...run race gas, make power. Taking material off the chamber is going to further lower the SCR that's why I told him to actually calculate what his SCR is so he can make a more educated decision.
 

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60 footing
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Discussion Starter #10
how do i calculate the CR ?
 
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