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Unread 05-08-2014, 02:21 PM   #1
chaceb94
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4.0L ignorance

So I destroyed my '95 YJ's 2.5L. I decided to go ahead and grab up a 4.0L not because I need anymore power in the woods, (the 2.5 has to be the best 4 cyl. I have ever encoutered) but because I would seriously love some more power on the road. However, that doesn't mean I think road performance is more important than trail performance; I really want to have both.

Anyways, I've been doing a ton of research, and originally I thought more HP would make me happier, but now I'm reading that all the things I thought I wanted (crane cam, stainless headers, gasket matched exhaust ports, and all the rest) are likely going to hurt torque in the low to mid RPM range. I've been wheeling long enough to know that I only occasionally ever get above 4000 RPM in the woods so I don't really give a **** what my HP and torque are at high RPM.

So my question to you guys is: What parts should I buy for the 4.0L I'm rebuilding? Stick with stock stuff or will the performance parts give me what I really want: High torque at low to mid RPM? Please don't say to stroker it. I know more stroke more torque, but I'm not made of money here so just save it.

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Unread 05-08-2014, 02:22 PM   #2
EugeneTheTJ
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A stock 4.0 is a pretty damn torquey engine. Ever driven one offroad?
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Unread 05-08-2014, 02:33 PM   #3
Wheelin98TJ
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Since you're doing a motor swap, I'd forget about the I6 and do a V8.

The I6 is not much motor for all that work.

With a V8, you get low end torque and horsepower, so its perfect for wheeling and on-road use.
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Unread 05-08-2014, 09:24 PM   #4
Ryanmccartney
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to swap to a 4.0l you will need a ax 15 tranny if you have a manual. different wiring and motor mounts. Your more then half way there for a v-8

My dad had the iron duke 2.5 I had a tired 4.0l and my transmission was hard to get in second gear. I was trying to figure it weather to rebuild motor and tranny or do a full swap.

I decided on the v-8 and I'm very happy with it

It gets the same fuel mileage as the 4.0l and I go up hill at any speed turning 35" tires.

I went to a automatic tranny
Hope this info helps

Best of luck with your decision

Rye
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Unread 05-09-2014, 05:09 AM   #5
StanF
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Seriously, the OP didn't ask about V8s - let's not start the "you are an idiot if you don't do a V8 swap" again...

OP, I think stock is probably where you want to be. You'll love the extra power and the 4.10 gears will be great with your 33s. Save your money on the special engine parts and apply it to a future 8.8 swap

One other thought...Rebuilding is pretty expensive. I just did the same swap as you (2.5L to 4.0L). I found a 1998 TJ engine with about 100K on it for only $500. That fit better with my budget. And I figure that the engine will last me 10 years or more. You may be able to find an engine with less miles that doesn't need to be rebuilt...
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Unread 05-10-2014, 01:02 PM   #6
AMC-COMMANDO
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I would stay away from the V8. The I6 has just about the same HP and will get much better fuel mileage. Cheaper to drive and will get you further down the road without killing your wallet. Plus it is a much more affordable swap. I took the 360 out of my 72 Commando and replaced it with a stock 4.0. I love it. You can't beat the 4.0! They are pretty easy to find in wrecked Cherokees for under 500 bucks, with low mileage. My 93 4.0 had 105K and picked it up for 400 bucks. Also just grabbed a 99 4.0 with 115K for 450. And I got to see both run before they were pulled. The 99 is going in my 75 J20.
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Unread 05-10-2014, 04:17 PM   #7
BrokeWJ
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Quote:
Originally Posted by chaceb94 View Post
So I destroyed my '95 YJ's 2.5L. I decided to go ahead and grab up a 4.0L not because I need anymore power in the woods, (the 2.5 has to be the best 4 cyl. I have ever encoutered) but because I would seriously love some more power on the road. However, that doesn't mean I think road performance is more important than trail performance; I really want to have both.

Anyways, I've been doing a ton of research, and originally I thought more HP would make me happier, but now I'm reading that all the things I thought I wanted (crane cam, stainless headers, gasket matched exhaust ports, and all the rest) are likely going to hurt torque in the low to mid RPM range. I've been wheeling long enough to know that I only occasionally ever get above 4000 RPM in the woods so I don't really give a **** what my HP and torque are at high RPM.

So my question to you guys is: What parts should I buy for the 4.0L I'm rebuilding? Stick with stock stuff or will the performance parts give me what I really want: High torque at low to mid RPM? Please don't say to stroker it. I know more stroke more torque, but I'm not made of money here so just save it.
It sounds like you're happy with your low-RPM performance currently. If you pushed your lower torque curve up some, you can likely end up exactly with the same torque low-rev torque as you had or more. Typically there's more of a downfall when idle or off-idle transition quality degenerates. With good FI, that won't be your issue.

That said, since you're going to a larger, torquier motor into a 4-banger geared truck, I'd spend the cheap money on slight steps up from stock that will offer light upgrades without hurting torque much.

Quote:
Originally Posted by EugeneTheTJ View Post
A stock 4.0 is a pretty damn torquey engine. Ever driven one offroad?
Yes. I'd hardly stay away from a V8, or completely discount a V8 swap- but a 4.0 is quite a step up from a 2.5. The 4.0 is about on par with most modern V8s in torque production.
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Unread 05-11-2014, 09:52 AM   #8
chaceb94
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Thanks

Yeah my dad's Rubicon has the 4L and I love to drive it around. I wouldn't go v8 mostly because of the extra weight on the front end, but I now feel much better about my decision to swap in a stock 4L with AX-15.

Thanks again. --Chace
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Unread 05-11-2014, 11:52 AM   #9
Wheelin98TJ
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Quote:
Originally Posted by StanF
Seriously, the OP didn't ask about V8s - let's not start the "you are an idiot if you don't do a V8 swap" again......
OP asked about an engine swap so it makes perfect sense to talk about swapping in a V8.
Quote:
Originally Posted by BrokeWJ
The 4.0 is about on par with most modern V8s in torque production.
Not really. For example, my small V8 makes more torque at 1,200 RPM than the 4.0 does at it's peak.
Quote:
Originally Posted by chaceb94
Yeah my dad's Rubicon has the 4L and I love to drive it around. I wouldn't go v8 mostly because of the extra weight on the front end, but I now feel much better about my decision to swap in a stock 4L with AX-15. Thanks again. --Chace
Many of the popular V8 swaps do not add any weight. The 4.0 is a heavy motor. The V8 I have weighs about 50 lbs less than a 4.0 I6.
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