1987 Jeep Wrangler (YJ)?

[Jerome]

Currently have the OEM 4.2l 258 CID I-6 mated to the Aisin AX-15 tranny, would like to go to a V-8 (304 or 360). What would be the challenges to make this happen? Will the V-8 bolt to the current tranny or should I change both?

 

[destroyeron13]

The AX-15 is fine for small V8s. If you're running stock tires and lift the stock axles should be fine as well.

 

[G-Fire25]

If the 4.2l wasn't stock, and they didn't change the rear and front end, then you'll have to change that. A V8 has too much torque for the gears in them. You might have to change them even if they did change them to something that would work for a Straight Six.

 

[Joe]

You'll have to change both. The AX-15 is a medium duty transmission and can't handle the V-8 nor can it bolt up. The challenges are going to be the deepness of your pockets (expect to spend in the thousands), and the time you have to make it happen (expect months of down time). You may also have to swap out the rear axle for a stronger one so you don't break the shafts. Powerful swap, but it will unbalance your rig. Go for the smaller V-8 or better yet: rebuild your current engine into a stroker. MUCH less work and you get a huge boost of power all the same.

Good luck!