Off Roading 4.0

[Boomer II]

I'd like to get a little more umph outa my inline 6. It's pretty much set up for rock crawling and does great at that, but on the highway with the NP435 transmission it's pretty much a dog. The gap between 3rd and 4th is a lot like a NV4500, so I get my butt kicked on steep inclines. Any ideas on the cheapest way to gain a few horses, chip, throttle body???

 

[MMcKenzie]

I assume by 4. 0 you are talking about a Jeep. What kind and what mods so far? I have built several in my time, Wranglers, CJs, Cherokees, ect. so I might have some ideas.

 

[Boomer II]

The engine is stock, out of a 91 Cherokee. Jeep is an 86 CJ-7, NP435 transmission, Dana 300 transfer case, Dana 44's with Detroits front and rear, 4/10's and 33" tires.

 

[willysrule]

I've see some pretty wicked Jeep 4. 0's built, there is a place on the net that has tons of performance 4. 0 stuff... search around at the link at the bottom of my post, two guys that run Jeep motors in my club have used there stroker kit... if your only running 4. 10's you could gear down (numerically up) a little more too... . my CJ isn't driven on the street anymore... I have an SM420 with the 7. 07:1 1st gear and 5:38:1 gears in the axles... it's pretty low :-laf



Here's that link... .

http://cliffordperformanceshop.com/site04/home.htm

 

[MMcKenzie]

Clifford does make some great stuff for the 4. 0. In this case I think the first thing I would do is to swap to a set of 4. 56 gears. Your drivetrain is great and the 300 is one heck of a t-case but unless you have swaped in a set of 4:1 low gears in it they had some pretty tall gears for true four wheeling. Sticking some 4. 56s in your pigs will help in two ways. One, it will get your highway RPMs back to where they should be so you have some better grunt at interstate speeds. Second it will help your over-all low gear ratio for your 4wheeling and rock crawling by helping to make up for the Dana 300 high ratios. I had a similar set up in my 86 CJ-7 and it worked great. Good Luck.

 

[Bob4x4]

I have 4. 56 gears with 32" tires on my jeep and could still use a bit more gear on the trail but it is pretty good on the road. I have a flowmaster muff,high performance PCM,and a cold air system from AFE. That combo is enough to chirp the tires in 3rd gear . The AFE system made a nice improvement by itself. The PCM requires 92 octane. The flowmaster is strong enough to support the weight of the Jeep a time or two.



Bob

 

[Boomer II]

My transmission has a compound low, a bit lower than a T-18 and is only a 4 speed, so it's screaming at 65 mph. Climbing passes is where I get kicked, third is too low and fourth is too high. If I go lower in the diffs then my top end on the highway would really suffer. I just want a bit more HP W/O tearing into the engine. I'm very happy with the offroad crawling, the compound low will get me as slow as I need to go.

 

[MMcKenzie]

Sorry Boomer, I miss-read your post. The good thing is your engine is a 91 model. Anything before 90 is a pain to find performance mods for. I tried several things on mine to boost it up a bit with out tearing into it. The obvious ones are a less restrictive intake, and better flowing exhaust. The only problem with the intake is if you are in the mud a lot, you might have some problems. Some other things to try would be a bigger bore throttle body, performance ignition system (MSD), performance injectors, and header. I had these on mine, and all together will give you some good seat of the pants gains. The great thing is the 4. 0 in my opinion does take well to modifications, good luck.

 

[Boomer II]

Thanks guys. MMcKenzie, have you tried a chip? I looked into those a while back, but didn't delve too far into it. I guess I'll have to pay to play, LOL.

 

[XJSuperman]

Chips don't seem to work well with the jeep 4 and 6 cyl motors (not counting the new 2. 4L and 3. 7L).

Do a header, high flow muffler and cat BUT keep the stock size dia exhaust tubing... you need the back pressure. ALso a bored TB and TB spacer will give a little more mid range oomph. You could try and run an electric fan setup... this frees a couple ponies and is easier on the water pump. You could also port match the intake/exhaust manifold as they are not done well on the 4. 0L engines.



An easy thing is to swap in the intake manifold from a '98+ XJ motor... this gives about 20HP to the earlier HO motors and is proven from many sources. It has equal length runners and the runners are rounded.



Your other option is to stroke it. Basically a 4. 2L crank in the 4. 0L block. Makes about 270 HP and 300 TQ (sometimes more).



And yet another option... run a 25 shot of nitrous. It wouldn;t be enough to blow the motor and it would be on demand when you needed it. I have a buddy that did this in his XJ and it works well.



For my money I;d do the late model intake manifold swap, header, TB and spacer. These things should give a good bit of giddyup to what you already have and won;t kill the bank.

 

[MMcKenzie]

I agree with XJ, skip the chip. I tried one for about a week and sold it. I could hardly tell I had it.

 

[Boomer II]

That's good to know, I appreciate the information.

 

[cyborg]

I have a 91 XJ LTD. Love it!! KJs are so lame, always in a ditch.



I swapped in mustang 5. 0 injectors, adjustable MAP, Borla SS exhaust (best sounding).



I want to build or have built a hot rod motor for it. But could never find a good source.

Quadratec offer some crate motors a while back.

 

[XJSuperman]

Cyborg go to either www.jeepsunlimited.com or www.pirate4x4.com and look up "4. 0L stroker". Beware both of these sites provide LOTS of good info BUT you have to wade through LOTS of BS and on the jeepsunlimited site the search function is not always good.



You could probably do a general websearch for the 4. 0L motor and have HOURS of reading. Most folks who have done the stroker LOVE it and it will really make the XJ get up and GO.

 

[willyslover]

OOOOOR ..... you could just drop in a nice 383 stroker and be done with it J/K ya

very available, cheep, parts everywhere,adapters available, ... many good reasons to do it as your going to spend over a grand on what you need for the 4. 0 MHO