What have you guys done to your 4.0 for more power that didn't break the bank?I will upgrade the air intake and the exhaust but is there anything else I am missing as I am not familiar with what is available.I see some headers available but wonder if they are worth the cost??

if you're looking for low end power there's not much you can really do. imo the headers not worth it on an otherwise stock engine. there are cams and stroker options available if you want to dive into it.

I don't agree. Long-tube headers, 6 into 1 or 6 into 2 with a crossover/merge collector/X-pipe should show noticeable improvement in torque Plus, inline sixes have room for headers that V8s don't. Check out the old standby, Clifford Performance.

R.

Replace with Hemi.

Well if I wanted a payment for a hemi I would buy one lol.The Jeep was given to me free.I can't leave anything alone so I am exploring cost effective mods.
I picked up a K&N air filter NIB for $30 and I will modify the air box a little.I will do my own custom exhaust and the idea of headers seem like it would help the torque/midrange a lot I just don't want to spend $500 on it.
Probably not much else to do unless it blows up but it was worth asking.

take the giant muffler off and put a dynomax on it,other mod is to cutout the little snorkel in front of the airbox for more air.anything else starts costing

If it's an early 4.0, a later intake manifold is susposed to be worth about 10 horsepower.

The late 4.0's had cylinder head that were crack prone and did not flow as well as the earlier heads. The heads are not a bolt on swap, but can be swapped. I believe some brackets must be fabricated and perhaps some other changes made also. Do some research before attempting to swap the heads.

Have you given the engine a through tune-up and made sure everything is functioning as it should?

I just recieved it with 164k on the clock.It has been sitting for 1.5-2 years only being started intermittently due to a bad transmission.It fired up and ran smooth all the way home.Wires look to have been replaced and the air filter is new.
I have a host of maintenance items I am doing such as replace all fluids,check brakes,front end,new tires,etc.
It is a 98 model and I won't to any BIG changes unless I have to go into the motor for other repairs one day.It isn't a hotrod but I like more power/efficiency when I can have it reasonably.

My daughter has one in a '01 Cherokee. Great engines - smooth and torquey - but not screamers. Hers has 135k and I understand they regularly go 200+k.

When she got it it had an open element cone type air cleaner added. Probably higher flow than OE but it was sucking warm engine compartment air. The OE setup, which she put back, draws cool air from in front of the radiator bulkhead.

There is potential for meaningful power upgrade with compression, cam and head porting. With 165k, short of a full high po rebuild, I'd personally just run it and enjoy it as is.

They do indeed run forever, I worked at the Kenosha plant that made them they made millions of them and it was pretty much the same old cast iron 7 main bearing design since the old 258 and even back into the 50s/60s AMC straight 6.

I have had several go 300,000 miles plus without any sort of engine repairs except waterpumps. They are decent power wise, IMO a lot better than most mid sized SUVs as is I wouldn't mess with it as people have said there are really onlyminimal gains to be had without "building" one and spending $$$.

Isn't the 4.0 a 9.0:1 engine? So pump gas compression gains would be moderate at best.

On the other hand, I bet there is some power locked up in the ports.

If you're really into it, the 258 crank as stroker is quite popular in Jeep circles.

R.

I have done several stroker motors, here is what you are looking for.
1. 2000 and newer intake,
2. a crack free exhaust manifold, there are many listed on ebay that replace the stock one.
3. 96 or newer exhaust head pipe, you will recognize it because it goes infront of the oil pan.
4. You can put 5.7 hemi intake and exhaust valves in it for cheap, don't do a chevy valve conversion DAMHIK,
5. an oversize throttle body helps,
6. I use a 258 amc crank, 4.2 rods and then H802CP pistons that were cnc dished to lower the compression down to reasonable levels, offset grind the crank .020 and shave the block so you have a .000 deck height.
7. you want a 7120 casting head, they have the best flow, and with some minor porting and polishing you get a lot of flow improvements
8. and you can look into an adjustable fuel pressure regulator to compensate for the mods you have done....my 94 wrangler stroker acts like a v-8 but needs premium and my wife's 98 TJ is getting 19 mpg without a stroker, just the intake and exhaust manifolds. Tim