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Thread: rover v8 interchangeability

  1. 22nd February 2010, 07:24 PM #1
    fitzy
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    rover v8 interchangeability

    From what I have been told , that is a 3.9 is just a bored out 3.5, and a 4.6 is just a stroked 3.9. And that a 3.9 and a 4.0 are the same except for the extra main bearing bolts.
    Would that mean that a 3.5 and 3.9 crank are the same, and 3.9 /4.0 and 4.6 pistons are the same.
    What I am looking at is reducing the capacity of my low k good 4.6 down to 3.9/4.0 to compete in production class.
    I could by a 3.9 that would be an unknown and spend $$$ getting it right or if my theory on interchange ability is correct get one of my old 3.5 cranks reground and use that.
    Any thoughts.
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  2. 22nd February 2010, 07:45 PM #2
    RoverP6B
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    3.5 and 3.9 blocks are quite different in that the latter have more ribbing on the outside along with different block cores. Main bearing caps and block registers are also different.

    3.9 and 4.0 litre engines are completely different in that the latter have large journal crankshafts and feature cross bolted main bearing caps. Connecting rods and pistons are distinct and cannot be swapped between the two capacities.

    4.0 and 4.6 litre engines feature different crankshafts, connecting rods and pistons. Neither a 4.0 or 4.6 crankshaft will fit into a 4.2, 3.9 or 3.5 litre block.

    Increasing the capacity of a 3.5 block by boring out to a 3.9 weakens the block compared to using a factory made 3.9 block. The latter was designed with that capacity in mind from the start.

    A 4.6 block is a large journal crankshaft block where as a 3.9 is a small journal crankshaft block, with different main bearing caps. You can use a 4.0 crankshaft, rods and pistons in a 4.6 block.

    Ron.
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  3. 22nd February 2010, 08:11 PM #3
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    discomuzz
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    What he said!
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  4. 23rd February 2010, 08:27 AM #4
    PhilipA
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    Buy the book "How to Power Tune Rover V8 Engines" by Des Hammill
    Veloce Publishing
    ISBN 1-903706-17-3/UPC 6-36847-00217-6

    If you google the number the book is reproduced by Google and you can read it free I guess.
    It will answer all your questions.

    Regards Philip A
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  5. 23rd February 2010, 08:33 AM #5
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    nzlandies
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    Also have a look at this site, especially if you want to go fast!!

    Eliot Mansfield's Twin Turbo Chevy Powered Range Rover Dakar 4X4 Kit Car
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  6. 23rd February 2010, 07:24 PM #6
    fitzy
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    Would anyone know the price of 4.0 short motors at the moment. A few years ago you could get them for $2000.
    I would probably pay that for crank, rods, pistons and labour.
    I am wary of paying $1000 for a used 3.9 that turns out to be a dog, and the time and inconveniece of fitting and f-ing around.
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  7. 23rd February 2010, 09:55 PM #7
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    whitakerb
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    Just stick the 3.9 plenum cover on. No one will know any better...

    Ben
    Cheers,

    Ben.

    Team W4 - WEBSITE

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  8. 24th February 2010, 05:45 PM #8
    fitzy
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    That would be cheating.
    I paid a lot about 6 years ago for a 4.6 long motor installed drive in drive out as it was my daily driver then, shortly after I gained a company car and the rangie has only seen social and a few competition runs. From past experience I am wary of second hand parts that you can't verify visually as being sound. I also wouldn't get as much for the 4.6 as I know its worth and would have no use for it apart from a dream of putting an eaton blower on top and putting it into a BRG 67 MG as a sleeper, when I drive it I will wear a twead jacket and cap and also smoke a pipe.
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