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Thread: from low to high compression pistons

  1. 1st February 2010, 05:31 AM #1
    phuma Guest

    from low to high compression pistons

    I drive a low compression 4.0L V8 - doing a rebuild on it, and the pistons need replacing. Is it worth going to high compression pistons? Can you even do it? Will the gains be worth it? What disadvantages?
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  2. 1st February 2010, 06:56 AM #2
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    p38arover
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    I had HC pistons fitted to my LC 4.6. You will need to change to premium fuel.
    Ron B.
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  3. 1st February 2010, 06:59 AM #3
    phuma Guest
    The fuel is what is worrying me - here in South Africa we only get one grade of fuel depending on where you are. Coast = 95, inland = 91 / 93. That is too low for the HC pistons I think?
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  4. 1st February 2010, 02:08 PM #4
    PhilipA
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    Seeing you have the engine apart you could remove some material from teh combustion chambers to lower the CR by about half a point which should be enough to run on 95.
    There is plenty of material which shrouds the Inlet valves that can be removed.
    Regards Philip A
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  5. 1st February 2010, 04:14 PM #5
    RoverP6B
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    The difference in maximum power delivered between a HC engine and LC engine is in the order of 5%, assuming all else remains unchanged.

    The difference is only at higher rpm, as it is my understanding that a LC engine actually delivers more power up to approx 3000rpm from which point the HC engine will catch up and then slowly pull away until max rpm is reached ( approx 4750 ) at which point the difference will be 5% or so.

    Is your vehicle an automatic or manual?

    Personally, I would leave well alone. The ecu will be constantly retarding the ignition timing to avoid pinging which will only reduce power being delivered. MUCH better to be able to use all the ignition timing and hence all the available power by running lower compression as opposed to the alternative.

    Ron.
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