Wondering when Jeep switched from 4.0 to 4.2? Which do you consider the better one?

 

They went from 4.2 to 4.0.

 

The AMC 4.2 was never available in the XJ.

The 4.2 was in the YJ until 1990, and was available in the full size cherokee, CJ, j10 and j20 pickups and some others.

 

Huge difference, 4.2 is carbed. XJs never had a 4.2 but YJs did, my 87 has it. The 4L makes more HP, torque and has fuel injection. I can hop in my XJ and go, my YJ has to warm up a bit. The 4.2 was used for a long time and the 4L was it's replacement.

 

4.2L makes a lot more torque on the low end, the stroke is longer. 4.0L is way more fuel efficient and has better top end. Plus MPFI is vastly superior to any carb setup in an offroader, if not any vehicle.

Put 4.2L crank and rod into a 4.0L and make a monster engine. Best of both worlds.


Read here: http://en.wikipedia.org/wiki/AMC_straight-6_engine

 

Doesn't the 4.2 make its peak torque at 1200 rpm? I haven't looked at the specs recently but I thought it was 1200 for the 4.2 and 1800 for the 4.0.

While the 4.0 makes more torque on paper the super low rpm power if the 4.2 has it's advantages in the real world.

I know there I an actual stroker kit for the 4.0. I'm assuming the hybrid 4.2/4.0 salad speaks of is essentially a stroked 4.0.

 

Yes that is one version of the stroker. Another version is basically the same but with aftermarket pistons.

Edit: And 4.0 rods.

 

Doesn't this make it a 4.6 or close?

 

4.5 with stock bore.

 

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