Iowa Chapter Director
Join Date: Jul 2002
Location: Ames, Iowa
I would just put the 4.2 crank in your block if anything, why mess with another block. And if you want to assemble it in a different block, do it on an sc block, you need to use an sc block for your supercoupe.
I personally wouldnt go with a 4.2 crank unless you plan on not making a lot of power. I have seen the 4.2 go to 400rwhp but that was on a centrifugal blower, which puts a LOT less stress on the rotating assembly since it makes power up higher. The low end power of the roots m90 puts a lot of stress on the internals. So if you arent doing a lot to your car then it may be okay, but remember that there's a reason you have a forged crank.
the 4.2/3.8 split-port heads are totally different from your heads so you cant use them without a custom lower intake manifold, but the intake valve is larger at 1.9" and the exhaust port is shaped a lot better for increased velocity.
1988 Notch Mustang: - 438W, direct port n2o, t56
2003 SVT Focus: - SCT X3 tuner