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post #1 of 5 (permalink) Old 06-13-04, 08:50 PM Thread Starter
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3.9 to 4.0

I have a 3.9 MPI which I want to rebuild in the near future. Iwas told to rebuild a 4.0 instead.
What else needs to be changed besides the engine. ie manifolds,computer etc.
Any assistance would be greatly appreciated
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post #2 of 5 (permalink) Old 06-14-04, 01:33 AM
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Re: 3.9 to 4.0

Depends, if you were goin to rebuild a 4.0, probably better to stick with the stuff that comes with it, assuming its a long motor, else, the computers are different, manifolds are the same if its MPI i believe, and i think the head is also common. Someone correct me if im wrong

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post #3 of 5 (permalink) Old 06-14-04, 02:03 AM
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Re: 3.9 to 4.0

if u wanna use the 3.9 log manifold and sesnors no need for new wiring loom and ecu. plug n play as afr as fitting the 4l engine
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post #4 of 5 (permalink) Old 06-14-04, 06:21 AM
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Re: 3.9 to 4.0

yer if u use the ecu from a 4lt instead of a 3.9 mpi ecu, u will probably need a smartlock module and ignition barrel... easier just to use the 3.9mpi with the 4lt engine

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post #5 of 5 (permalink) Old 06-19-04, 09:31 AM
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Re: 3.9 to 4.0

3.9 was only the figure they were allowed to advertise them due to there being 17 different sized pistons 3.9L was the smallest capacity the engine could theoretically be the largest being 4.1L they still average 4.0L so you won't get any more power
it's not worth the extra hastle when chances are you could only be decreasing the capacity

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