LS6 with AFRs

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Jan 1, 2008 | 10:58 PM

#21

RareBreed0295

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From: Bishopville, SC

I have decided to just stick with my set of PRC 2.5s right now. Something is wrong with the tranny right now so hopefully i can still get some good power out of the PRCs and a custom grind cam.

Jan 1, 2008 | 11:05 PM

#22

JonCR96Z

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From: Asheboro, NC

Quote:

Originally Posted by hammertime

Leaving the heads unmilled will make the car lazy on the bottom end, and leave a few HP on the table across the board.

Uh, don't think so. It depends on the rest of the setup. Unmilled heads actually flow better. I don't plan on milling my AFRs and my SCR will be right at 11:1, depending on how far the pistons are out of the hole and what head gasket I end up using. My DCR will be around 8.4-8.5:1. Theres more factors at work here than milled heads.

Jon

Jan 3, 2008 | 05:20 PM

#23

1stz06

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From: Houston, TX

Try to find out how much the AFR's have been milled. I have seen night and day differences in numbers between LG's G5X3's with 64cc and 59cc heads.

440-460 would be my guess.

J.R.

Jan 3, 2008 | 08:11 PM

#24

hammertime

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From: Smithton, IL

Quote:

Originally Posted by JonCR96Z

I'm not sure how you are arriving at 11:1 without milling. Even at .010 above the deck, the heads are 66cc unmilled (you are using 205's, right?), and would need so thin a gasket as to leave an unsafe deck clearance just to get that high.

I get 10.87:1 SCR using PianoProdigy's calculator, and come real close at 10.84 using all the following: 66cc head, 3.94 x .040 gasket, and .010 negative deck clearance. A 232 lobe would need to be installed on a 108 to 106 degree centerline to get the DCR to 8.4 - 8.5:1.

It is my understanding that the gains in compression outweigh any reduction in airflow up to about .040", but airflow begins to fall after that. Since the original poster was suggesting a cam with 7 degrees more duration than your 232/236, he'll definitely benefit from the increased compression. Using the same SCR above, the MS4 (239/242 111+3) comes in at a DCR of just 8.1:1. Milling to 59 cc should remove about .042" from the head, the absolute max before we compromise flow any significant amount.

Valve clearance may also be an issue at this duration, so its a tough call between just taking .030 to end up at 61cc, or cutting valve pockets for additional clearance and milling all the way to 59cc. In my opinion, .012" isn't much leeway, and a cam with that duration and RPM potential could use the extra PTV clearance.

Sorry for the long response, but my short answer was meant to imply that the SCR and DCR would benefit a great deal from milling.