Engine How much can you safely bump the 4.0L and not hurt the reliability?

[bennylava]

One of the things that attracts me to the 4.0L for the old Jeep I'll be fixing up, is it's reliability. But how high can you go with HP and TQ and still have excellent reliability?

Next question!

How much hp and tq is really needed for light, and medium trails? We'll never be doing mudding or advanced trails. Would 300hp and 300tq be enough for a medium trail, while also feeling like the jeep was "fast" on the highway? Fast for a jeep anyway. Thanks!

 

[Manic Mechanic]

I have a stock built AMC 258 i6 / 4.2l only mods being EFI headers and GM HEI. It has plenty of power for trails and I've had her over 100mph. You don't need anything near 300/300 HP&tq for what you are trying to accomplish

 

[jzak]

Old man rant here, but why the heck would you buy a vehicle that was never designed for speed, and try to get 300hp out of it???? I've read these kind of posts a million times before. Its always, Do I need a LS engine swap, Do I need Dana 60's, Do I need a 6-inch lift to go off roading? Simple answer is NO! If you wanna turn a perfectly good CJ into some modded Frankenstein, it's a free country, but its gunna cost ya 25-50 grand, and a lot of broken transmissions, rear diffs and axles in the process. And in the end you'll be going up Hell's Revenge at Moab, and an unmodified CJ3 will skip past you, and you'll wish you never changed a thing.

 

[bennylava]

Oh I should have said I don't have an engine and Transmission . The old stuff died before I got it, and was yanked out, but then the project was abandoned.

So I have to get something in there, or someone on foot would pass me on the trail let alone an unmodded CJ3 lol

 

[Manic Mechanic]

I'd grab a complete 4.0/5 spd from a Wrangler drop it in. Don't worry about HP the inline 6 has plenty of power for a lite weight Jeep like that

 

[hole]

Axle gear ratio will have more to do with moving the Jeep down the road. 2.73, big tires and a 6cyl will give it a dog like impression on any type of hill. You can overcome it some with higher horsepower. Ask yourself outloud , so we can chime in, what is your goal with this rig? What gears are in it now?

 

[KRUPP]

300hp and 300lb-ft are way more than you need for a little Jeep, on, say, 35s. I don't have near that with my current AMC 258 i6 / 4.2l and it does excellent while wheeling. Hwy driving is a different story. But, I don't mind tooling along and the mountain passes make it struggle, even with 4.56:1 gears.

I've never "built" a 4.0, so I can't add to your question about how much you can reliably get out of it if bored x stroked, etc.

As Manic mentioned, I'll agree that the 4.0L is known as a good motor - so long as you don't get a Lemon like I did in a '01 TJ I had back in the day. I kept a long list of all the shi$ I had to replace on that thing over just a couple years.

What Transfer Case , if any, do you have? This will help steer you too.
If you do go the 4.0 route though, the NP231 Transfer Case behind the Transmission in a lot of 4.0s was mediocre in a lot of ways. I had to rebuild mine after the chain said "adios".

To add to what hole mentioned above, your Jeep really is a blank canvas now for whatever you want to create.

 

[bennylava]

Axle gear ratio will have more to do with moving the Jeep down the road. 2.73, big tires and a 6cyl will give it a dog like impression on any type of hill. You can overcome it some with higher horsepower. Ask yourself outloud , so we can chime in, what is your goal with this rig? What gears are in it now?

Well there's a lot of light and medium trails in my area, so the dream is to be able to drive it to the trails. And not have to trailer it. That's why it would be nice to have a few highway abilities. Like being able to do 70 mph, and not be at 4,000 RPM's. Or whatever the exact number would be.

I don't know the ratios on a tremec 6 speed, but maybe the 6th gear could help a lot if the diff has 4:10 gears in it. No idea what Transmission I should go with. But we won't be doing any heavy trails or water that's over 1 foot deep. Last thing I wanna do is destroy the thing after building it.

I'm kind of a new to all this, in case you couldn't tell

 

[hole]

Try going to Grimmjeeper (website) , where you can play around with virtually every Transmission /Transfer Case /tire size combo known to man to see what your RPM's will be at any speed. Next question is what size tires do you intend to run?
No familiarity with the Tremec 6 spd, but the overall length might be problematic with a CJ's wheelbase and the need for a driveshaft . I would also recommend looking at Novaks site for Transmission info.