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Chad911sc |
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#1
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Member ![]() ![]() Group: Members Posts: 80 Joined: 24-September 24 From: Florida Member No.: 28,374 Region Association: South East States ![]() |
I have my short block built and I’m ready to set my deck height. It’s 96mm bore with stock 71mm factory crank. This is a 2.0 2056 build. I have a Web 86a cam calling for approx 9:1 compression. I have 60cc heads with 3cc valve reliefs on my flat top pistons. If I plug all this into the calculator, I get 8.3:1 for my compression ratio if I set the deck height to .040 inch
After I set up the piston on the rod and bolt down the cylinder to the block, I get .053 inch from the piston to the top of the cylinder. My question is, what is the best way to proceed to get the 9:1 ratio with at least .040 inch total deck height. I am thinking that if I take off 6 total cc’s from the head, that will leave me with 54cc heads with the 3cc valve pocket = total 57cc’s. Bringing me now to the correct 9:1 compression ratio with the .040 inch deck height. If I am in the right ballpark, this means I need to have my heads fly cut….correct?? If this is correct, how do I go about calculating how many thousands of an inch do I need to have removed by the machine shop to remove 6cc from the head? I obviously will need to remove at least .013 inch total deck height get to my .040 goal, and that’s with no shims or head gaskets being used. Thanks for your time, Chad |
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technicalninja |
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#2
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Advanced Member ![]() ![]() ![]() ![]() Group: Members Posts: 2,531 Joined: 31-January 23 From: Granbury Texas Member No.: 27,135 Region Association: Southwest Region ![]() ![]() |
You're on the right track.
Altering the cylinder head will NOT change deck height. You will need to add a .013 shim between the jug and case. Don't trust a single deck reading. Do it on all 4 and adjust shim to the tightest one. Use the same shim on all. You want the top of the jugs to be parallel to each other. Plot the shape of the depression in the head and figure out how much you need to trim off of the heads to achieve 9-1. CAD is the way to go for this. If you haven't verified the registers in the case are flat, you should before doing any of this. This is a known weak spot that "sags" with casting age alone (per Jake Raby). Also, CC the heads and the valve depression before doing any machining. I NEVER trust "published" numbers. I've seen too much variation in the past. I LIKE the trough style of valve depression, but I'd expect more than 3 CCs |
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