reednuts

Have a low miles 4.2 out of a 78 fsj and I'm looking to swap it into a 97 Xj. I've seen plenty of stroker chat and people putting 4.0 heads (job weld water holes) on old AMC jeeps but no one doing this. What obstacles should I expect to encounter? Any help would be appreciated

Jamie57

I already looked into it. For all the work you would have to do you'd still be about 40 HP shy of a stock 97 4.0.


Now if you were putting the head on the 4.2 IN 78 FSJ then you'd be doing something. Better still ditch the 4.2 and put the 4.0 in. Or use the crank and connecting rods in your 4.0 for a low buck stroker.
There is just no way to use the 4.2 short block and make more HP than a stock 4.0.
I know it doesn't sound "right" but hey it's still a tractor motor.4.0 or 4.2.

reednuts

Okay, that answers the question, so does it not increase the displacement while also bumping up compression? What am I missing here? This blows my mind...

reednuts

It's so confusing that it can be a 40 hp gain one way but the other it's -40hp, just very disheartening lol

salad

Why not just put the rods and crank into the 4.0L and come out with a stroker?

reednuts

Seemed a bit easier than disassembling a motor, having never done so