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Old 02-18-2004, 09:49 AM   #1
johncg
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Lightbulb Zetec compression rules of thumb

Hi everyone,
I am currently building the next rev of my Zetec motor and wanted to see if anyone has any rules of thumb for how much to shave a stock ZX-3 head to give how much compression (with stock bottom end). I'd be glad to compile a table with this information and post it to this forum.
Regards,
John


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Old 02-18-2004, 10:13 AM   #2
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Whats the stock stroke length and bore diameter? Using that and the stock compression ratio, you could figure out how much volume is left at top dead center, that will give you the amount of volume in the stroke vs. the amount of volume in the head. Use your target compression ratio you can the backpeddle to find out how much to shave off the head in order to get the ratio you are looking for. Be careful of too much compression tho, 11:1 is about the max on 97 octane. unless you want to go buy racing octanes. $$$. Have you also considered getting higher compression pistons? That does add interia to the engine's reciprocating mass though, the bain of a high revver.
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Old 02-18-2004, 10:21 AM   #3
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I am building up a stock bottom end (although I have installed ARP rod bolts). I invest most of my money in heads and head work.

I just bought a Ford Motorsports ZX3 head (ported, bigger valves, etc) but it comes unshaved. I also have a pair of Kent Focus2 cams (BTW, these are pretty aggressive cams). I think I want to use no more than 11:1 compression. I have jsut discovered that my current engine had about 0.078" shaved off which I think gives very high compression!

Anyway, I was hoping I could find a table of compression ratios for various amounts of head shaving for a stock bottom end and head to use as a guide.

Any help would be appreciated.

John
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Old 02-18-2004, 10:39 AM   #4
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You have a PM john.
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