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I have a 1986 CJ7 258 CI engine, Tranmission 4 speed unknown model. Trans case unknown model, rear end AMC 20 front end Dana30.
I also have a 69Nova(restoring), a Harley Davidson FXD 1997 model(runs very well). Things are now going well.
A 4.0 head on a 4.2 is still a 4.2. Crank and rod from a 4.2 into a 4.0 is a 4.5 and with various piston's or overbore's can be a 4.6 or 4.7 so they're not the same.
No. You're right, they're not exactly the same. But essentially, you are getting the same thing minus a couple tenths of displacement. You are getting the desirable stroke out of the AMC 258 i6 / 4.2l ...which is what it all comes down to and then capping it with an upgraded head that will handle more flow. You can always bore out a 4.2 for more displacement.....but it's meaningless really for a little more CID.
I've done all this and in the end, ended up with a 300hp+ 4.2 with ungodly torque.... And that was keeping it carbed. I essentially had the same to better engine performance as the guys I ran with who stroked their 4.0L's
The only upgrades I did were cam and pistons as far as the bottom end.
I have a 1986 CJ7 258 CI engine, Tranmission 4 speed unknown model. Trans case unknown model, rear end AMC 20 front end Dana30.
I also have a 69Nova(restoring), a Harley Davidson FXD 1997 model(runs very well). Things are now going well.
CJim7,
This is what I was thinking of doing....I'll try the 4.0 head swap and add a cam n springs into to it first. If it doesn't have the desired affect I'll do the below portion.... Only I think I'll get a head out of a junk yard along with the wiring harness...why not go electronic since I'm doing it anyway....
