Swapping a 258 for a 304

I have a 75 258 w/a t18 attached...also have a spare 304. My question is, will the bell housing and tranny fit the 304, or will I have to get a 304 bellhousing and different tranny adapters?


Thanks.......

 

This thread is important to my intrests.

 

The bell housing bolts right up, the frame horns for the 258 are differant. We used M.O.R.E mounts.

 

Flywheel is different.

And from what I have read, the power difference is negligible. Plus, the AMC V8's in stock form have notoriously bad oil pressure. 258's do not. If you are going to do it(I was) you might as well go with a 360.

High5

 

Re the power of the 304 v. the 258, the last of the 304s (heavily desmogged) in the 80s were really anemic, but the early-mid 70s 304s are a significant upgrade over the 258.

IMO the 258 is a superior design in terms of durability and longevity, but the 304/360 is still a good engine. A worn AMC V8 often has very low hot idle oil pressure, due to the aluminum timing cover wearing out. The timing cover houses the oil pump, and it wears faster than the rest of the engine. With low oil pressure, the rod bearings or cam will fail. High mileage 360 Wagoneers with a rod knock are very common.

JMO - depending on how long I wanted to keep the Jeep, I'd either hop up the 258 (easy) or swap in a 360/401 before I'd swap in a 304. 304 cores seem to be getting more scarce, and you might be able to find a buyer for your (good?) 304. Certainly a mildly warmed up 258 (cam, 4.0L head, 2V carb or FI, ignition, exhaust) will match a stock 304.

 

Sounds like I might be better off keeping the 258, doing some mods to it....something to think about.


Thanks for the feedback..

 

You can figure that HP is roughly proportional to cid, so 304/258 = 18% increase in HP. That's a nice boost, and you'd feel it, but I don't know that it's worth it. Also, I think your Jeep will be worth more if it has the original drivetrain - the 258/T-18 was a great combo - the owners that had them really liked them.

What axle ratio? 4.27s are better, and would make a big difference in performance.

 

timgr.....orig enging/trans was a 232/3speed...which I still have....72 tub was shot so I picked up a 75 tub...then later the 258 combo...right now all I have is a frame and two axles
from the 72....ratios front and rear are 3.73's..just trying to figure out which way to go before I either rebuild the 304...bored 40 over once already, so may have to go 60 over... or recam and use the 258...thought I would stick with the carb,,it has a Clifford alum. intake with a 2100 motorcraft on it...eventhough I'm not fond of headers...always seem to leak.
Its not going to be a rock crawler or anything like that...its just my fishing/hunting rig, weekend driver...it was lifted, but rode like a tank. I removed the super heavy duty springs and installed originals..should ride better....


Thanks for the info

 

what are some good power upgrades you can do to a 258? Mine runs awesome but a lil more power would be nice. I am still a Jeep rookie (2 months) so the I6 is completely new to me.

 

Don't get me wrong I love my v8 ( not stock), but you can make the 6 run pretty darn good. Prob cheaper than the 8. Buddy had a cj7 about 20 yrs ago. We did the cam, ign, and an Offy manifold set with small 4bbl. Man did it wake that thing up. Maybe 25 yrs, man I'm gettin old.

 

My 72 had the 304 2 barrel originally, and against the 6 cyl I drove, there was no comparison. The 304 felt like it had way more power and torque and was generally more fun to drive. Not to say the 6 cant be built, but for the fun factor IMO the V8 cant be beat. I switched out my 304 for a 401 just because I had a rebuilt one and thought it would be fun, but I never had a compaint about the power of the 304.
Then again if your concerned about gas mileage, go with the 6.
I do agree though, if your going to put in a V8, and half to rebuild the 304 anyway, go with a 360. They are a dime a dozen everywhere, and just as cheap to rebuild as the 304, and the power difference is huge.

 

Ah, where to start?

I'd suggest you start a new thread with this topic.

In the meanwhile, I'd suggest you start at Google and try "AMC 258 performance" and read everything that looks relevant. Depending on how much you have to spend, you can go cheap with an ignition upgrade (Duraspark/TFI or HEI), stock late model 2V manifold with a 21xx Motorcraft carb, and late model exhaust manifold with a free-flowing exhaust. From there, the sky's the limit ... the 4.0L head is probably the next big mod, a better cam, EFI... the GM TBI is a great mod, or go all the way to the Mopar MPI. You can substitute a 4.0L block 60 over, using your crank, and get a 4.6L engine (285 cid) engine. You can go as high as 5.0L with a specially ground crank and enough money http://www.ajeepthing.com/stroker-motor.html