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Old 01-16-2013, 06:32 PM
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just cc'd the pistons and heads

just got done with the heads and pistons.the pistons held appox. 22.5cc's (dished) and the heads toped off at 65cc's .the block has zero piston to deck height .this is in a 421sbc 4.155 bore by 3.875 stroke JE pistons with 6" rods .running a solid roller xr286r comp cam.with this info what would be the diff.in compression with a .039 versus a .041 head gasket.the heads are dart iron eagle 215's.a little worried about pump gas .PS did this with a veterinary syringe and plexy glass could be a little off.is this enough info. for the dcr.?

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Old 01-16-2013, 06:48 PM
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Google or search this forum for several c.r. calculator links, they're free.
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Old 01-16-2013, 07:02 PM
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just cc'd the pistons and heads

.039 head gasket- 9.951 cr. and 7.693 dcr, .041- 9.951 cr and dcr 7.724.
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Old 01-16-2013, 07:18 PM
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Quote:
Originally Posted by jtz55 View Post
just got done with the heads and pistons.the pistons held appox. 22.5cc's (dished) and the heads toped off at 65cc's .the block has zero piston to deck height .this is in a 421sbc 4.155 bore by 3.875 stroke JE pistons with 6" rods .running a solid roller xr286r comp cam.with this info what would be the diff.in compression with a .039 versus a .041 head gasket.the heads are dart iron eagle 215's.a little worried about pump gas .PS did this with a veterinary syringe and plexy glass could be a little off.is this enough info. for the dcr.?
I think we can muddle through it.....
861 cc's in the cylinder
22.5 cc's in the piston crown
65 cc's in the chamber
0 cc's in the piston deck height
8.5 cc's in the head gasket
Mr. Gasket Ultra-Seal Head Gaskets 5801G - SummitRacing.com
Total 957.0 cc's
Subtract cylinder cc's from total and find 96.0 cc's
Divide 957 by 96 and find 9.97:1 SCR with a 0.038" squish.

Intake valve on the XR286R cam closes at 50 degrees ABDC @0.050" tappet lift.
Using these figures in the KB calc.....9.970, 3.875, 6.000, 65.000,
I get a DCR of 7.989:1 (call it 8:1).

I like to see in the vicinity of 8.5 on this calc, so I'd be thinkin' that to show that number the motor would need either more SCR or less cam. An intake closing at 40 makes 8.55:1 DCR. Then again, with a range of 3000 to 7000, this big cam might make up the difference in flow and let the motor make more power than a smaller cam with the "ideal" DCR. At 8:1 DCR and a 0.038" squish, I don't think there's much to worry about in the detonation department on pump gas. I'd run it with the big cam if it was mine.
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Old 01-16-2013, 08:19 PM
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how about this cam instead?

111313-06S NA 279 279 247 247 .585 .585 106 102 .022 .022 1,2,5
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Old 01-17-2013, 09:25 AM
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You are fine as is with either gasket. It will make great power either way..
92+ octane gas.


Be sure to verify VTP clearance.. Set the valve lash cold about .004" less than cam card hot lash spec
with that cam.

Your fine and it will GLH.
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Old 01-17-2013, 05:31 PM
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thanx for the calculations tech.thought might be a little higher so iam happy with close to 10-1 wont have to worry about detonation while cruising around on hot summer days in central il.F BIRD what if any experience do u have with comp. cam products such as springs ,roller rockers. do u have any other preferences like manley or isky.or would u stay with the same manufactuer as the cam?
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Old 01-18-2013, 05:07 AM
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Quote:
Originally Posted by jtz55 View Post
thanx for the calculations tech.thought might be a little higher so iam happy with close to 10-1 wont have to worry about detonation while cruising around on hot summer days in central il.F BIRD what if any experience do u have with comp. cam products such as springs ,roller rockers. do u have any other preferences like manley or isky.or would u stay with the same manufactuer as the cam?
i have use that exact cam in a BBC.. Buy the complete K kit and install exactly as instructed. Make sure you get the cam button end play correct. Make sure you verify cam to stroker connecting rod clearance. and verify VTP clearance.
Call comp cams if you want. They are there to help. They have premium beehive springs too for this, if you want.
Its a good cam makes great power. Set the lash -.004" cold.

The complete K- kit is a great way to go . K12-772-8 for that cam.

I like Scorpion roller rockers.

I have never used a Isky roller cam but would not hesitate to do so.
I like an use their flat tappet stuff. Its one of my go to preferences for
a flat tappet cam.

I have a Comp cam in my car now.

I think you have made a good choice. Post back on how you like this combo when you get it all done.
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