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Performance ??? Little Help Please

812 views 2 replies 3 participants last post by  lostboy 
#1 ·
I have an 1989 258 4.2 litre 6cyl, it is carbuerated and old, i am replacing that motor with a brand spanking new one.
The question is, can it be powerful, from headers to cat back then exhaust is all the ways of modifying horsepower, is there anything else, like modifying the air cleaner that sits atop the carb. or maybe a new carb. please let me know, i realize i should have put this in the engine forum but nobody goes there. Thanks again.
 
#2 ·
I too have an'89 with 4.2. You didn't say auto or manual, I've got auto.(love it) I bought it 2yrs ago from the original owners(who took great care of it). I had 108K when I bought it, and I put in a new(remanufactured) Carter Carb myself at 130K miles. I haven't made any fine tuned adjustments as of yet, but it runs 80% better. When I step on the gas the Jeep actually accelerates! If I ever have the money, I would put in a Mopar fuel injection kit. Other than that, I'm gonna run this thing till she blows. If and when that happens, I'm gonna try to get a newer 4.0 or a Chevy 4.3. The chevy engine is sweet with lots of torque and acceleration. (My wife has the Astro van) This 6cyl engine is the same one Chevy puts in their 6cyl full size trucks. It is actually the small eight with two cyl. removed. A cheaper alternative to the carb (I would try it first) is to change the air filter, plugs, wires and fuel filters. This should make an immediate difference as well. It would also be less costly before doing the carb replacement.
Good luck,
Tommy
 
#3 ·
Good luck on the engine swap;Maybe if I had a garage I would do the same,but I have an'89 4.2 that''s actually in pretty good shape. The compression and oill pressure are excellent for an engine with this mileage(123,000).
That being said, I recently purchased the mopar mpi kit and am waiting to install it. I also will do the 4.0 head swap at the same time.I have heard that this combination will increase horsepower to about 225 without losing the low end torque. Cooling system is in the process of being upgraded as I write this.
Later plans call for a tranny swap and differential upgrades....
If this motor fails in the future,I would just get a rebuilt short block to replace it.
I guess it would be the same as a stroked 4.0 when it's finished.
 
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