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post #1 of 5 (permalink) Old 09-29-01, 08:48 AM
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Compression Ratio's (E7s / Gtps)

I need some advise, I am currently home porting a set of Gt-40p's. I am going to fit larger valves 1.94/1.54 (stock 1.85/1.46) and I want to mill the heads to up the compression ratio to a something similar to the 220kW AUII heads. I think the P's are a 59cc chamber, WHAT IS THE E7 CHAMBER CC?? I'd like a compression ratio of 9.45:1, how much would I get milled off around 20thou? I read that the rough estimate for a small block Ford factory type casting is 1cc for each .007" milled?


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post #2 of 5 (permalink) Old 10-01-01, 08:35 AM
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Ok i am going to reply to my own post here.
E7 casting are 64cc combustion chambers and I read the GT-40p is 60 (so say factory tolerences 59-60cc).

So not even milling p's would raise compression on my engine no? ANYONE?

post #3 of 5 (permalink) Old 10-01-01, 09:41 AM
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well actually milling ya heads will increase the c/r not sure how much to remove my tfs were shaved to obtain 9.9:1..
check out the ford racing catalogue pg 115 its explains how to work out c/r's..
hope this helps, also keep an eye on valve clearances not that i need to tell you about that

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post #4 of 5 (permalink) Old 10-03-01, 07:20 PM
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haha thanks brett.
heres what my mate Sean Meldrum told me,...

the original iron GT-40s from FMS or from a Lightning were 65cc. From a Cobra they'd be milled from the factory. I think the rough estimate for a small block Ford factory type casting is 1cc for each .007" milled. Figure approx. 4.3cc reduction.

A 59 cc chamber would have you at 9.5ish. 60 would be about 9.38ish. The nominal range for a P is 59-61. A .010" cut should shave a bit over 1cc. So I'd say .010-.015" should easily get you to 9.4:1

post #5 of 5 (permalink) Old 10-03-01, 09:54 PM
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On that subject came up with E7's 030Th = 9:5 about right ??. [+5cc for piston chamber & valve relief's} so 58 cc head c.chambers is what they go for..
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