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Thread: Head and manifold machining for higher compression on V8

  1. 19th January 2009, 03:53 PM #11
    up2nogood Guest
    Well, to be specific we have:
    * 9.35:1 engine 4.6ltr crate engine, kindly supplied by an AULRO subscriber.
    * 3.9 heads off an 8.34(?):1 (? as I can't recall exactly, but you know what I mean...). Engine ran tin gaskets, is an Oct 1993 S1 Disco engine.

    Compression ratio I am looking for must be in this range 9.8 - 10.00:1. No more than this as I don't want to have to machine the block at all.

    So I am happy to machine the heads, I do not want to machine the bores as they're too thin from standard and I don't really want to spend a fortune as I can get a Cosworth 4.6ltr engine for 1,500 pounds from RPI Engineering. Or I could just go the whole hog and Gen 111 Chev it. But I want to give the little fella a go before I give up!
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  2. 20th January 2009, 08:22 AM #12
    Traco
    Traco is offline Master Supporter
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    The way to raise the comp ratio on a 4.6 by changing pistons is to fit 4.0 litre pistons (not same as 3.9), available from Rimmers, RPI, etc. You can even specify a Coscast block/short engine with these included (at extra cost of course). The blocks themselves can also be bought (cheaper) from TVR Power, which is I believe where RPI source theirs.
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  3. 20th January 2009, 07:59 PM #13
    up2nogood Guest
    Thanks for the tip!

    Back to the 4.0 pistons, where do they take the comp ratio to?
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  4. 21st January 2009, 09:46 PM #14
    Waxenwane's Avatar
    Waxenwane
    Waxenwane is offline Master
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    You can always weld up the combustion chambers and have them machined to suit your needs. As for pistons J E engineering (John Eales) in the UK do 93.5mm and 94mm or bigger hi comp pistons.

    Make sure your wallet is very heavy though

    Another route is as previously mentioned is to use Holden pistons, 253 plenty of options there, cant remember which 6 cylinder pistons fit. Give Ian Shugg at Crankshaft rebuilders a tingle he has done a bit of fiddling in this department.
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