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Highest "safe" DCR for 92 octane?

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Old May 8, 2007 | 05:49 PM
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Default Highest "safe" DCR for 92 octane?

Hello guys.

I'm looking at a set of heads, and wondering if they'll be safe to use with my current setup on 92 octane gas, which is basically all I can get around here.

Using JROD's excellent calculator, I show SCR at 11.35 and DCR at 8.75. What do you guys think, is this too much DCR for 92 octane gas? Anyone with personal experience with similar numbers?

Thanks in advance...

P.S. This is on a car with bolt ons, 228/232 on 114+4 XeR lobe cam, and heads "would be" 59cc Patriot LS6 Stage IIs. Thanks!

Last edited by Higgs; May 8, 2007 at 06:05 PM.
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Old May 8, 2007 | 09:17 PM
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Do you have a good cold air system? How tight is your quench? The tighter the better. Does you car normally run cool or does it run over 200 degrees? The list could go on but you get the drift.
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Old May 8, 2007 | 10:12 PM
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Originally Posted by 1989GTA
Do you have a good cold air system? How tight is your quench? The tighter the better. Does you car normally run cool or does it run over 200 degrees? The list could go on but you get the drift.
Blackwing with fresh air access behind the bumper screens, DCR numbers were calculated using factory MLS gasket thickness, car runs a 160 degree stat that generally has the car running in the 180-190 range.
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Old May 9, 2007 | 08:27 AM
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Old May 9, 2007 | 10:32 AM
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I think you would be safer w/ a DCR closer to 8.5. If you would be willing to run cometic gaskets you can go w/ an 0.040 thickness and run 64cc chambers. This puts the DCR at about 8.52 w/ a quench of 0.033. It is important to tighten up the quench distance to resist detonation. If you are gonna stick w/ the GM MLS gaskets I would go w/ a 62cc chamber, which puts DCR at 8.43. Of course I do tend to lean toward the safe side.
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Old May 9, 2007 | 10:35 AM
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Use 1 step colder plug, the calc will reflect higher than actual so you'll be fine.
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Old May 9, 2007 | 05:11 PM
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He was origionally leaning towards a 62cc heads, but they were sold before he bought them. Also looking at a set of used 59cc, but I recomend against it due to the DCR. As you suggested if he was buying new a set af 64cc heads with the .040" Cometics would be the best setup. I was leaning towards the 8.4-8.5 DCR range, but nothing is set in stone and I could be leaning a little on the low side for safety.


Originally Posted by 5.3LJimmy
I think you would be safer w/ a DCR closer to 8.5. If you would be willing to run cometic gaskets you can go w/ an 0.040 thickness and run 64cc chambers. This puts the DCR at about 8.52 w/ a quench of 0.033. It is important to tighten up the quench distance to resist detonation. If you are gonna stick w/ the GM MLS gaskets I would go w/ a 62cc chamber, which puts DCR at 8.43. Of course I do tend to lean toward the safe side.
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Old May 9, 2007 | 06:46 PM
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11.35?? with only 92.. hmm.. pushing it.. but shouldnt be too bad..

why dont gas stations carry 93 anymore? Even the sticker on the gas door to my Typhoon says to use 93... i can only get 91.. and it seems to not like certain 91's too. sorry that was off topic
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Old May 9, 2007 | 07:32 PM
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Originally Posted by GR33N GoblinM6
11.35?? with only 92.. hmm.. pushing it.. but shouldnt be too bad..

why dont gas stations carry 93 anymore? Even the sticker on the gas door to my Typhoon says to use 93... i can only get 91.. and it seems to not like certain 91's too. sorry that was off topic
I'm planning a setup that has just over 11.35 static compression. With a 60cc head and a .040" gasket, this one will approach 8.65:1 DCR according to the calculator, but I'm going to keep my fingers crossed that the calculator is a little optimistic on DCR and that a tightened quence will keep it resistance to any pinging during the hot Louisiana summer weather using 92 octane.

Ben T.
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Old May 10, 2007 | 02:41 PM
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Thanks. Looks like I'm going to be better off with slightly larger cc heads and a better quench. Sigh, guess I need to pass up a good deal.....
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