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post #1 of (permalink) Old 11-17-2002, 09:16 PM Thread Starter
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Suggestions for 258/350

Yes i know this has been covered... I do realize how ell some of the other AMC engines work, but i am set on a 258 or 350. thanks anyhow. I searched found the pros and cons of each. But i could not find suggestions comparing the two with a highly moddified 258...

I am not in a stage were the stock 258 is going out. Would getting another 258 block, replacing the innereds (balancing and all), doing a 4.0 head (by a proff.) and MPI, be more or less produtive/cost efficiant, than swapping in a stock chevy 350 with TBI? In both cases i would hope to still run the AX15, but would it hold up? Thank you.
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post #2 of (permalink) Old 11-18-2002, 07:22 AM
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Re: Suggestions for 258/350

If you are talking about a really warmed up 6cyl or an 8, then I wouldn't keep the AX-15. It may last a while, but under hard use it would probably just be a matter of time before it quit on you. And if you are looking for V8 power out of a 6.... then you should probably just get a V8.
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post #3 of (permalink) Old 11-18-2002, 11:48 AM
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Re: Suggestions for 258/350

Take a look at clifford for parts for the 258. They say you can get just as much performance out of 6cyl and a 8cyl.
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post #4 of (permalink) Old 11-18-2002, 01:27 PM Thread Starter
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Re: Suggestions for 258/350

thanks, great site for bolt ons. Where should i look for the inards of the 258 to bring it to life? Cam sizes, compression, etc??
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post #5 of (permalink) Old 11-18-2002, 02:33 PM
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Re: Suggestions for 258/350

Take a look at my profile. My 258/4.0 head runs friggin awesome - not like a six at all! No idea on Hp, but lots of power everywhere.

Some things to consider...

1) A really stout built six will be more expensive than a 350 with TBI - at least the motor itself will. I had $3K in mine before all was said and done and I did the install. The flip side to this is that with a 350 I would have had to go with a different tranny --> more $$$, so the total package price would have been more. Additionally, the conversion is what takes up most of the price. Expect to spend $1K-$2K on getting a 350 in the Jeep - not including the price of the engine and that's before you buy a tranny. If you already have a 258, you don't have to buy all kinds of accessory crap getting it in the Jeep.

2) I am not sure what options you have out there in terms of a cam for fuel injection on a 258/4.0. Most of the setups I have seen require a stock cam. Most of my power is coming from a slightly warmer cam that takes advantage of the other aftermarket components. This also figures into your price though... last I checked the MPFI kit alone was around $2K.

3) The 350 will make more torque. Period. Accordingly it will also drink more gas and break more stuff.

4) Budgeting out this kind of thing as completely as possible makes all the difference in the world.

In terms of your specific questions: stick with stock innards for the short block and head unless you want to go racing. Balancing would be good. Spend some time figuring out what cam you want if you go with a carb. Stock pistons with the 4.0 head will give you plenty of compression. You will likely have to spend some time tweaking with it to get it to run well without detonation as is.

Let me know if you want any more from my experience. I'll be glad to help.
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post #6 of (permalink) Old 11-18-2002, 02:40 PM
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Re: Suggestions for 258/350

Well, all I can say for sure right now is that since you already have a 258 in your rig, it'll be easier to put another 258 in it instead of doing a motor swap. You already have the accessories, etc... to make the 258 work. Why bother swapping to a completely different motor if you don't absolutely have to??

Don't get me wrong, I am traditionally a Chevy guy (and generally in favor of dropping an SBC in anything that moves), but based on prior experience I'd say that sticking with the 258 will give you fewer headaches when you're wrenching. However, the more you modify that 258, the less reliable it is going to be... nothing against the 258 at all; that applies to ALL motors, though... you run an agressive cam, you wear out valve springs. You run more compression, you are more sensitive to bad gas. You run headers, you're more likely to end up with an exhaust leak. That's just the way it works.

Unless you have a line on a good deal (I mean REAL good) on that TBI 350, I'd look into the later model Vortec 350's pretty seriously... they make a LOT more power and are just as docile/reliable.

Honestly, though, if it was me, I'd look into building a one-off mild turbo setup for a (relatively) stock 258. Low boost, stock redline, and PLENTY of power for all but the most extreme situations.

But that's just me, and I'm kinda strange like that...
post #7 of (permalink) Old 11-18-2002, 04:48 PM
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Re: Suggestions for 258/350

Here's the way I see it; it's a question of how much power you want. If you want a lot, the SBC is the obvious choice. Pick any number you want above a very lightly modified 258, and it will be easier and cheaper to get it out of the 350.

I think that almost everyone on this board will tell you that a Jeep doesn't NEED more power than that, unless you're into sand or serious mud. So, how much do you want?

Also to be considered is that the 6 is easier to work on, cheap to run, and already there. Something else that might be a factor, but I've never seen it mentioned here, is the weight of the two engines. My guess is that the SBC will be a little heavier, but not enough to fret over. Anybody know the real numbers?
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post #8 of (permalink) Old 11-18-2002, 05:51 PM
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Re: Suggestions for 258/350

i would put a 4.0 head on the 258 with a split duration .262/.272 cam with the ford 32# injectors and the 97+ exhaust manifold and a grand cherokee 96+ intake.
this isnt horribly expencive, and most of it could be done in stages.
anything more will shred the ax-15...even this set up will if you are silly with the go pedal.
i would suspect that this set up would be about $1500 cheaper than the sbc with similar power. the weight is negligible...
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post #9 of (permalink) Old 11-18-2002, 09:59 PM Thread Starter
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Re: Suggestions for 258/350

Thanks, i will go with the 258. Sounds better and yes, the headaches of a sbc in the jeep. The kind of power i am looking for is common stuff. The YJ is my DD and it does not cut it on the hi-way and gas mileage is down to 10 mpg (on a good day). Off-road i have always has enough power, but it puked out in off camber situations, hence the reason i would like fuel injection or TBI... ALthough how complex are those FI set ups? The thought of loosing a carg to a computer kind of scares me. Can someone please shed some light???
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