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Cometics, .040 or .045?

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Old 04-03-2007, 09:15 AM
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Default Cometics, .040 or .045?

Going to order my head gaskets today. I was told, by a very reputable sponsor, that .040's on a stock short block would be a little tight. That you would have to be very careful with the .034 quench because of the loose tolerances.

Anyone had any problems with the .040?

The difference between SCR/DCR is 11.4/8.43 for the 040 and 11.25/8.32 with 045. But I've read the the ideal quench is .034.

Any thoughts, comments or suggestions on which ones to use?

Tried searching - all I get is a white screen...
Old 04-03-2007, 09:17 AM
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yeah .040 is a bit tight for a stock block. The .045 would probably be a better choise.
Old 04-03-2007, 09:50 AM
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I've seen .040 recommended a lot because of the DCR, but I wanted to play it safe and got a .045 and didn't look back. The DCR is a very important element of the combo and I'd think you'll be fine with a .040. However, PTV clearance could become an issue if you have aftermarket valves, and a lot of duration in your cam.
Old 04-03-2007, 09:52 AM
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.040 is more recommended more for the quench not the DCR.
Old 04-03-2007, 09:55 AM
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For an unmilled head the .040 Cometic is perfect. I run them and have no problems.
Old 04-03-2007, 10:38 AM
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PRC LS6 heads milled .030 with 2.02 valves. The dcr only changes by .15 but I was just trying to tighten up the quench a bit.

Think I'll wait for the forged internals, (next winters project), before I get too crazy with it...
Old 04-03-2007, 11:00 AM
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It all depends on you piston to deck clearance.

I have my slugs .010 out and with .050 gaskets = .040 quench, and at 12:1 no issues with misfires or detonnation.

Good range is on average .040 for street.
Old 04-03-2007, 12:02 PM
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.045's it is... Thanks guys




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