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Performance Mods for the 4.0

3K views 65 replies 17 participants last post by  jsawduste 
#1 ·
OK, as a recovering hot rodder and Jeep aficionado I am contemplating how to increase power and performance. My criteria is to stay within or at least in view of the stock configuration. I want to stay with the 4.0 so an engine swap is out.
My present setup is: Snorkel with K&N air filter, Free flowing exhaust, Electric fan, Stock drivetrain (3.07 Gears) with 33" tires.
My plan is to improve mechanical advantage by swapping to either 4.10 or 4.30 gears. I plan to go to the newer style 4 hole injectors and possibly an adjustable Fuel Pressure Regulator. I am aware it has been pretty much confirmed not to improve performance but it will insure better atomization and insure it is at optimum performance. I like the consideration of the horseshoe intake converting to the spring loaded idler. My understanding is the intake actually hurts performance. Beyond this all I see is internal engine mods. Not sure how far you can go before you render the OBD1 useless. Unfortunately OBD1 is what I have and will be what I will use. No advantage to lightning the rotating assembly as torque is what I want. I am sure there is a camshaft upgrade that will operate within OBD1 and you may be able to bump compression a bit. Maybe even squeeze some cubic inches by stroking it. I am wondering what has been done and the results. I am simply considering a plan for the future and find it interesting.
 
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#2 ·
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#4 ·
I was hoping for some lower cost home brewed tried and true performance mods. Full engin build and or a $2500 power adder seems outside my plan
 
#6 ·
If you want some oomph out of that jeep go higher in gears to 4.56 or 4.88 that will give you the seat of your pants you are looking for. You won't be able to go over 75 but who does that in a jeep anyways?

I for one am in the middle of combing my 4.2 and 4.0 for a 4.7 stroker and that's my big vote.
 
#7 ·
I really miss the power I had with 4:10 and 31's, the 35's took all that fun away.
 
#12 ·
DirectMatrix said:
Well now I just gotta know...what's the red led light on the dash for?:confused::D ~DM
That means the Flux-capacitor is ready....
😝
 
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#15 ·
Gearing is a given, getting some cold air from the snorkel and K&N. Wondering what a camshaft will do for 160K engine. Maybe some basic porting on the head. Opinions?
 
#16 ·
Gearing isn't going to be cheap, you'll need carriers front and rear based on your 3.07's. Then welcome yourself to the rabbit hole of what to replace those carriers with, lockers, LSD's, open, etc. Gears with master install kits and carriers are likely to cost you nearly $2k, particularly if you don't do the work yourself. I wouldn't go with anything taller than 4.56's with 33's. I'd like to have 4.88's with mine (have 4.56).

If you're willing to pull the head and go through a cam swap on an engine with 160k on it why not just build a stroker?
 
#18 ·
Gearing is a big topic so here it goes, and mind you this is well discussed. Waggy D44 with locking hubs $300 ISUZU Rodeo D44 LSD with 4.30 gears $175, purchase 2, transfer gearset up front. $650 plus ball joints, brakes etc $350 total $1000 with spare parts left over. Naturally more goes with the install but that is a long term plan. Stroker short-block build $1200 minimum. Headwork and cam Guessing $400 maybe $500. Wondering if the Horseshoe intake should be considered. I'm not looking to make a racer just don't want to downshift from 5th to 4th on a long freeway hill climb.
 
#19 ·
Gearing is definitely one of the best performance mods you can do. I bet you would be just as quick as a v8 on 3.07s by swapping in some 4.56 gears. I had 4.56 gearing on 31s with the stock 4.0L for 2 years and it would pull hard. For reference, I raced against my friend with a 2002 Volkswagen golf GTI (VR6) and we were side by side up to 60 mph.

I now have 4.10s after the rear pinion bearing went out. It is still pretty quick, but not quite as much oomph as before (better on the highway though which is what i wanted). Keep in mind jeeps are not really meant to go fast. In a jeep I just want quick acceleration at lower speeds and dont really need high end speed. I enjoy fast acceleration but i also enjoy living so i dont try for high speeds. Engine upgrades will get you more power, but with low gearing itll still be slow off the line. Most benefits would be seen at high speeds without upgrading gears. Gearing would be your best option because you will get the power at lower speeds, and can always upgrade the engine later if you want the high end speed.

If you have a chance, find someone with a jeep and proper gearing to test drive. My buddies jeep has 3.07s on 32s (also 4.0L) and it doesn't have kick. It gets moving, but not very quickly.

4.10s vs 4.56 gearing on 31s:
4.56 - rpms at 75 mph were about 3k (it's been a while, use a gearing calculator for better accuracy ). Top speed was 95 mph
4.10 - rpms at 75 mph are about 2600. Top speed is 100+

Gearing might be expensive, but so are engine upgrades. Gearing will need to be done eventually with bigger tires, so might as well do it first. 4.56 gearing would be best with 33s and will bring you back to the stock gearing to tire size ratio. You could even gear down to 4.88s if you want even better acceleration and sacrifice a little highway crusing comfort. You can always settle for 4.10s by swapping in axles out of a 4cyl which would be a lot cheaper (i paid $400 for front and rear axles with 75k). Best bang for your buck will for sure be gearing in my opinion. Go for 4.56 gearing at least if you can afford it, otherwise swap in 4.10s at the bare minimum
 
#20 ·
Ok I have been building hotrods and racing for over 30 years and I said right up front that Gearing is a given so I know how to capitalise on mechanical advantage. I had 33's" and 4.10's on my 94 Wrangler, that was a nice compromise. My question is or was just like 8.8 swaps, exterior slave cylinder swaps, Grand Cherokee Alternator swaps there are tried and true mods that the forum mostly universally agrees are worth the $ and effort. Clearly the forum has not universally come together on 4.0 performance mods. No engine tuners for OBD1, no cam recommendations (From Experience, I can read a cam card), no intake upgrade, only exhaust, the forum is fairly split on cold air intakes. Most members are not interested in building power with the 4.0, members that want power do V8 swaps which vis a vei mean drivetrain swaps, bastardized vehicles and the costs go astronomical. I guess on this journey I will be the guinea pig
 
#22 ·
I always try to get multiple gains from a mod. I read somewhere that the horseshoe intake was essential to the conversion to the spring loaded tensioner. I have read several reviews about the intake so at best it's a transparent change. The only benefit is the power steering pump may be better or stronger but the only advantage is the tensioner is self adjusting and easier for belt changes. So unless one is given to me I don't see the $ and effort being viable. I have seen cam swaps kill an old engine but modern fuel injection makes engines last remarkably well so I see the risk as minimal and it could be used in the stroker or stock rebuild. Since it is a low RPM motor head porting will as most other mods only give minimal results but it appeals to my sense of things operating at their balanced optimum. Really just blending and the removal of casting flash and lines is all that needs to be done. I guess that a stroker build is what it will be. No replacement for displacement. Staying true to reliability I guess I need to find some stroker builds that maintained the stock components. I also need too re-review the horseshoe intak application to see if it is worth it. Seems like I read where someone cut away some of the aluminum between the runners to help reduce heat soak. I bet hood vents would help as well.
 
#23 ·
What about larger throttle body?
http://www.extremeterrain.com/bbk-62mm-throttle-body-yj-tj-1724.html
A friend bored my stock one out for free. It did seem to make a difference.
I seem to remember of a video that some one did it at home. I will have to look for it.
From what I have read the spacers really do not do anything.
I am running a Comp Cam. I put it in when we did my engine rebuild. The engine was bored out at the same time so really I can not tell you how much of a difference it made.
Here is a pretty good video.
 
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#25 ·
The K&N will shorten the engine life if used if dusty conditions.
It lets in dirt.
The stock airbox is very good. The duct between the two is the choke point. Just replace the duct.
The stock airbox is a cold air intake. It has a duct that gets air from behind the headlight.

Some of these mods (The horseshoe intake) actually lost 5 horsepower on the dyno.

JEEP 4.0L MYTH BUSTING - TRUE LIES
http://www.fourwheeler.com/how-to/engine/154-0911-jeep-4-liter-engine-myth-busting-true-lies/

These mods ^^^
are more than half the cost of the supercharger I want.
 
#27 ·
awesome read, seems that changing the tube between the airbox and throttle body is it. If you do a supercharger it would be interesting to know if it bolts to the stock intake, if so then the horseshoe intake may help. Id say a high quality long tube header would be a performance addition. The factory lean tune may call for hood vents. BTW I retained the factory airbox with my snorkel. I have K&N's on virtually every vehicle I have owned for the last twenty years and I love them.
 

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#28 ·
I would try to find another head and do a home port on it Charlie. 1bolt over on jeepstrokers has a good post about the 0331 heads from 2000 and up about the better intake and exhaust port shapes that they have casted in from the factory. If your going to cam it you might as well shine up a head, shave .010 off it and then use the newer intake and 62MM TB to take advantage of the cam. You might get the adjustable fuel pressure reg that has been talked about in the past as well. When that is all said and done I bet you could get into a stroker for less then 1k if your penny wise. Junkyard late 4.2 crank polished, commonly available KB pistons. The rest is just a simple 4.0L rebuild kit and things you already have setting in your jeep.>:)
 
#29 ·
That is a real option to consider. I believe I will replace the convoluted elbow from the airbox then start parts collecting. Before I commit to a stroker build I will get the regear done. I have a long list of parts I am collecting. I have dropped off several forums so Jeepstrokers may be a new forum to consider. This feels much like hotrodding my old Harley Davidson. Not sure the results are worth the effort.
 
#31 ·
The Golen used all the OBD1 stuff with no issues I assume? That is an awesome rig you are building, I have been following it closely.
 
#33 ·
calpbs said:
The Golen used all the OBD1 stuff with no issues I assume? That is an awesome rig you are building, I have been following it closely.
Yup, everything except the injectors, need to get 24# injectors.
 
#34 ·
I have to do axles and get my mechanical advantage first then I can do an engine build. My exit and subsequent re-entry into jeep ownership has me playing catch up. I had to have a good looking ride but I also want strength and reliability. I can do a few more minor mods while collecting parts. I appreciate all the recommendations.
 
#37 ·
All good points that make sense based on perspective. I was hoping for and did get a few home brewed mods that make small differences. I like the reliability factor of the 4.0 and it is the best option for what I am doing. The engine article I read really laid it out well and without major changes the engine operates in a narrow window. I believe mechanical advantage (Re-Gearing) will most likely get me where I want to be. As the engine has 160K+ a rebuild will be looming so maybe a core to rebuild/build with minor enhancements such as porting and gasket matching along with a minor bump in compression and maybe a cam. Possibly an increase in cubic inches. but axles would be first.
 
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