327 Compression ratio - Team Camaro Tech
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post #1 of 14 (permalink) Old Apr 15th, 08, 10:11 PM Thread Starter
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327 Compression ratio

I would like to have about 9.5 to 1 in the motor I am building. The .040 flattops I am using said they would be 9.1 to 1 with 64cc head on a 327. How much would they have to surface off the head, to get it to 9.5 or 10 to 1? How much could you take off and still get proper alignment of the intake? The heads are the good 492 castings. I am using Federal Mogul forged pistons (same as the old TRW or Speed Pro's). L2165's. Thanks for any input.
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post #2 of 14 (permalink) Old Apr 15th, 08, 10:34 PM
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Re: 327 Compression ratio

I would only shave enough of the heads to true them and make up the compression by decking the Bock within the distance between the Piston Top at TDC to your present Deck Height which normally is .025" providing them pistons have the STD Compression Height. That way you can use a .030" to .039" composite Head Gasket to optimize Quench and vary compression. Also you will not upset GM Specs and require Intake milling... Etc. I would say taking .020" off the deck would be safe.

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post #3 of 14 (permalink) Old Apr 15th, 08, 11:16 PM Thread Starter
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Re: 327 Compression ratio

If the piston is .025 "in the hole", why not just clean up the head, and use a .015 or .020 gasket? That would make your "quench" .040 or .045. You should have taken .010 or .015 off the head, then gain another .015 to .025 using a thinner gasket, so you have taken off .025 to .040, would that get you a 1/2 point in compression? Will this work?
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post #4 of 14 (permalink) Old Apr 15th, 08, 11:35 PM
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Re: 327 Compression ratio

I agree same results but you have more room to play within the Quench Specs if you deck. Your proposal Quench is .025" + .019" (Shim Gasket) = .044" and no more options. My proposal considers future options; such that, .005" + say a .030" (Composite Gasket) = .035 Quench which is optimum and you got another .009" to work with available gaskets plus you can always take more off the head if you ever decide you want more compression pending Piston to Valve clearances.

Just my opinion ))

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post #5 of 14 (permalink) Old Apr 16th, 08, 06:03 AM
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Re: 327 Compression ratio

FM is basing the L-2165 .040 at 9.1cr on .029dith and a .037 gasket.

A .015 gasket gets you to 9.6 my calcs.

Or if you prefer to cut the head instead, you would need a 60cc chamber. SROT is .006 per cu in,
or .024.

Or you could cut the block about .025 .

Me... I'd run the friggin shim like folks(includin GM) have been doing for hmmmmmm 4 decades now.

Tim Smith

Last edited by 77wolf10.85; Apr 16th, 08 at 06:35 AM. Reason: had .24, needed an oh
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post #6 of 14 (permalink) Old Apr 16th, 08, 10:55 AM Thread Starter
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Re: 327 Compression ratio

Thanks WOLF that is good info. Had no idea what gaskets etc. FM used in figuring the CR. That is probably what I will do. Less machine work too.
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post #7 of 14 (permalink) Old Apr 16th, 08, 11:38 AM Thread Starter
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Re: 327 Compression ratio

What is "SROT"? Got the new set of forged pistons on EBAY for $200.! A rare decent EBAY deal. I don't think too many are into 327's anymore. But it's fine by me. I am thinking of running a solid cam. It might sound something like the mighty 302!
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post #8 of 14 (permalink) Old Apr 16th, 08, 11:40 AM
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Re: 327 Compression ratio

the 333 im building is going to get about 10.4:1 with a 4 valve relief flat top, .015" deck height, and .025" compostie type head gasket. I would highly suggest getting the .025" compostie type head gasket over a shim steel.

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post #9 of 14 (permalink) Old Apr 16th, 08, 11:49 AM Thread Starter
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Re: 327 Compression ratio

Are you running 58 62 or 64cc heads?
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post #10 of 14 (permalink) Old Apr 16th, 08, 04:45 PM
 
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Re: 327 Compression ratio

GM spec'd our old engines usually right at .025" DITH piston for use w/ .020" thick steel shims! Make's a good .045" quench that tighten's up a schosh w/ a bit of piston top carbon coat..

This is why Fel-pro's #1094's at .015" are dandies by me b/c they make a .040" quench..

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post #11 of 14 (permalink) Old Apr 16th, 08, 05:12 PM
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Re: 327 Compression ratio

Quote:
Originally Posted by OK69 View Post
Are you running 58 62 or 64cc heads?
Sorry, running 58cc aluminum heads.
Btw, they can mill from 64 to 58. The people I bought my heads from new buy a 64cc core and mill to 58 cc's
I would suggest low cc's unless the shop can't get the milling right and your intake will seal poorly?

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post #12 of 14 (permalink) Old Apr 16th, 08, 08:02 PM
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Re: 327 Compression ratio

Quote:
Originally Posted by OK69 View Post
Thanks WOLF that is good info. Had no idea what gaskets etc. FM used in figuring the CR. That is probably what I will do. Less machine work too.
srot std rule of thumb

fm's website has the .029 dith in their table. I figured the gasket thickness on my comp rat calc with their .029dith, 5cc vr's, and 64cc heads. They list the cr for each cc of head, so I just worked backwards.

Idunno where they get .029 dith for sure....but I guess it's probly based on 9.025 - 5.7- 1.671 - (3.25/2) = .029

The 1.671 is the cd(compression distance). Which is cl of pin to top of piston. Their piston and I reckon they know what it's cd is.

Tim

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post #13 of 14 (permalink) Old Apr 17th, 08, 04:43 PM
 
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Re: 327 Compression ratio

I use .025" and go myself.

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post #14 of 14 (permalink) Old Apr 17th, 08, 05:27 PM
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Re: 327 Compression ratio

The smaller your combustion chamber, the more efficient it is, and the easier it is to burn more of the mixture.

I would deck the block to zero and mill the heads to 58ccs. Then you could run a standard head gasket at .041". Just make sure the intake angles are okay and check your pushrod length for sure.
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