• Hello Guest, we are proud to now have our Wiki online that is completely compiled and written by our members. Feel free to browse our Jeep-CJ Wiki or click on any orange keyword when looking at posts in the forum.

Thinking of rebuilding 4.2

Thinking of rebuilding 4.2

shepherd1

Jeeper
Posts
84
Thanks
0
Location
bowling green,oh
Vehicle(s)
1974 CJ5
So I'm thinking of rebuilding my AMC 258 i6 / 4.2l and was wondering how hard it would be to get close to 300hp out of it. I seen some adds of rebuilt motors pumping out 240hp with 9.1 comp and stock heads. I was thinking or using a 4.0L head with porting and 10.1 comp pistons and an aftermarket cam for it. So I guess I should ask has anyone hop up their AMC 258 i6 / 4.2l 's? I've been building Drag racing motors for along time (not the little 400hp motors either, last one built dyno'd @ 1134hp) I know how to build them ,but 1st with this motor.
 
Take a look at JP magazine website they just built a I6 with a turbo that made huge numbers :chug:
 
Take a look at JP magazine website they just built a I6 with a turbo that made huge numbers :chug:
yeah but that motor isn't one you'd use for everyday street/trail use.
as far as getting 300hp out of a AMC 258 i6 / 4.2l its doable but you gotta think built out the <-BAD WORD-> stroker motors aren't even pushing that much, and if you can get that much out of it, how long will it last in a daily driver or hard trail abuse. honestly you'd be better off spending your money on a small block, but then again you probably know that. you'd be doing it just to say you could right?
 
Anything is dooable, If you have unlimited funds. I guess my question would be why? A boat load of money and effort to build a completely marginal engine. Clifford did a short experimental run of AMC 258 i6 / 4.2l engines some years ago, and got some pretty good numbers out of it. The valve train was so modified that they had to cut the top out of the rocker cover and weld another one on top of it to make it high enough to clear. But even Clifford saw the folly in trying to do crazy things with a AMC 258 i6 / 4.2l . Personally, I love the AMC 258 i6 / 4.2l . I don't think there's a tougher engine with a better track record on the planet, or one that is so willing to produce maximum torque and power with so few modifications, and not have any health issues afterwards. But being a 6, it has it's limitations. It was the perfect Jeep engine, designed to be more than the Jeep would ever need to do It's job. Mudders would argue the point, and say they need RPM's to dig holes, but the Jeep was never really designed to be a mudder, It's a climber. If I were to go nuts with an engine, It would be a GM. You could probably build 2 for the cost of trying to nuts on a AMC 258 i6 / 4.2l and have way better results.
 

Jeep-CJ Donation Drive

Help support Jeep-CJ.com by making a contribution.

Help support Jeep-CJ.com by making a contribution.
Goal
$200.00
Earned
$0.00
This donation drive ends in
0 hours, 0 minutes, 0 seconds
  0.0%
Back
Top Bottom