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  1. #1
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    Yes | No

    m30 technical question?...

    ok heres what i have been thinking just wondering wether someone who knows the m30 might be able to verify this for me...the m30 is an interference enginge with a very high compresion like 10.5.1 or similar? these motors run a flat top piston, ok heres what im wondering;if i was to put dished pistons in this motor to bring the compression ratio down to around 8.0 (im rebuilding a 3.3 litre m30 turbo motor for my e21)will this overcome the 'interference' of the motor?,were there a low compression piston available for our motor at all,also please if somone knows what is the factory set redline for this particular motor...pulled from 1981 euro spec ausrtalian delivered 7331 automatic sedan (straight multi peice manifold)

    Thankyou for your time
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  2. #2
    wally~e28 from GCCV
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    Re: m30 technical question?...

    Use UK spec pistons.

    the m30 comes in the euro (10 to 1) and US (8 or 9 to 1) engine variants. the euro models have a high domed piston, and the us models a dished variant. The use the same head, just change compression with different pistons.

    The absolute easiest road to lowering the compression would be to slap on a later model e32/e34 m30 b35 head, as it has a larger combustion chamber (65cc versus 58cc from memory) which would give you a drop also.

    good luck

  3. #3
    e28/e24 butlertron 5000 in NM
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    Yes, and bigger valves on the b35 head too

    -
    Daniel Leahy
    '85 528e- e30 323i head, 325i cam, polished outside/ported inside intake
    manifold, 535 injectors, I.E. shorty headers, 533 AFM, e30
    320i ecu plug'd into 325i fuel injection, 3.46 diff. 341k on chassis, 5k on motor.
    '83 528e- Auto trans, new paint and interior. 325i cam, still dog-slow. 175k.
    '88 US spec M6- Not mine, still pimpalicious. 140k

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