I have to swap engines and I have a line on a cheap 4.0/AX15 combo to replace my 2.5L. I never really read about anyone keeping the 4.0 after doing a buildup. Why is that? Just lack of power or the 4.0 is just not a good engine for crawling?

Thanks

I have the stock engine and tranny in my 94 YJ. 4.0/999 I have full width axles and 39.5" TSL's I love it. Could have more power but that will come in time, but I love the gas mileage

Well, I'm certainly not as hard core as the guys on this board, I guess, but currently I'm planning on keeping my 4.0. I think it makes a great rock crawling motor.

Keep in mind that I'm keeping my 4.0. That is not the same as swapping one in. The biggest reason I'm keeping it is because it's there, runs perfectly well, and provides more than enough power for what I want to do. If, however, I had to swap motors for some reason, I personally would probably go the sbc route.

Having said that, the 4.0 is a reasonably powerful, tourquey, trouble free engine. starts all the time. idles like a champ over obstacles. never burns oil. never gives me one once of grief.

the 'idles over obstacles' thing is often overlooked, I think. One person who has a 5.0 ford swap done told me he had a lot of problems maintaining control because even the slightest throttle input sent WAY too much power to the rear wheels. From my motorcycle roadracing days I know that there is such as thing as too much power, in that if you cannot dial in the amount of power you want (between 0 and the maximum available) then the power is not tractable and may overwhelm your available traction.

I find this happens with V8 guys. As soon as they get a V8 they tend to use tire spin a lot more. Could just be cuz it's fun. Anyway, my point is the 4.0 is a very tractable, controllable engine. That's not to be undervalued,IMHO.

Also, less power means less breakage, all other things being equal.

On the negative side, another buddy doing a 5.0 swap discovered that the 5.0 ford V8 is about the same weight as the 4.0 - which means the 4.0 is not saving you anything in terms of weight. And I'm basically unimpressed with most horsepower gaining mods available right now.

All my 2c. And if I had the money, I'd probably go V8 for the same reason most other people do - because I COULD, and because it's FUN.

a buddy of mine runs dana 60's front and rear with 39's and a 4.0 and AX-15. he said when he nukes it he will swap in a 350.

Chris G.

Originally posted by The Rockslut
I have the stock engine and tranny in my 94 YJ. 4.0/999 I have full width axles and 39.5" TSL's I love it. Could have more power but that will come in time, but I love the gas mileage

What mileage do you get? And what gears you running.

Thanks!

I was running 4:56 gears with 38.5" SX's and now have 5.13 gears with 39.5" TSL's.

Not sure of the exact mileage but it is around 20 mpg. Sucks more going up the freeway to the Con.

There was a time (about 4 days ago :rolleyes: ) that I loved my 4.0. I have to agree as above though, if its there, keep it, but if you are already doing a swap to get one, go V8.

Well, don't want to disagree or anything, but the 4.0 is rated for around 17 mpg (imperial gallons) stock. That might equal 20 miles/us gallon, stock. But those ratings were extremely optimistic - I've rarely seen mileage that good in either my YJ when it was stock or now highly modified, or at any time in my bone stock cherokee. I find the 4.0 to be a bit of a hog.

HOWEVER, we recently went on a run with a 4.0, a stroked 4.0, and a 304 V8 in reasonably good shape. The highway killed the V8 - 3.55 gears, I think, 33 inch tires, auto tranny. That thing sucked like 3/4 tank getting to the trail head. I went through less than 1/4, the stroked 4.0 slightly more than 1/4.

Bottom line I guess is that any fuel injected motor is probably going to do better mileage wise than a carb'd engine generall speaking, but when comparing fuel injected motor to fuel injected motor, I suspect my friend with the 5.0 swap is going to end up getting better mileage than my stock 4.0, because it is going to take less effort for the V8 to push big tires.

One major disadvantage that no one else listed is length, swapping to a V8 or V6 can gain you quite a bit more drivetrain/driveshaft length, be it for doublers, long tranny's or longer shafts (or all the above).

That said I'm far (real far) from hardcore like some of these people, but I'm currently building my jeep, and plan on keeping the 4.0 for quite a while, just a good strong engine. Power isn't anything like a good V8, but the new 4.2/4.0 hybrid stroker kits are really intreging, and may convince me to hold onto the 4.0, when it comes to rebuild time.

Chad

Originally posted by ChadLloyd
And I'm basically unimpressed with most horsepower gaining mods available right now.

What mods have you done and how much did it improve it?

Originally posted by ChadLloyd
Well, don't want to disagree or anything, but the 4.0 is rated for around 17 mpg (imperial gallons) stock. That might equal 20 miles/us gallon, stock. But those ratings were extremely optimistic - I've rarely seen mileage that good in either my YJ when it was stock or now highly modified, or at any time in my bone stock cherokee. I find the 4.0 to be a bit of a hog.

HOWEVER, we recently went on a run with a 4.0, a stroked 4.0, and a 304 V8 in reasonably good shape. The highway killed the V8 - 3.55 gears, I think, 33 inch tires, auto tranny. That thing sucked like 3/4 tank getting to the trail head. I went through less than 1/4, the stroked 4.0 slightly more than 1/4.

Bottom line I guess is that any fuel injected motor is probably going to do better mileage wise than a carb'd engine generall speaking, but when comparing fuel injected motor to fuel injected motor, I suspect my friend with the 5.0 swap is going to end up getting better mileage than my stock 4.0, because it is going to take less effort for the V8 to push big tires.

Thats cool. My rig pulls that mileage all day long any day of the week. If I put my foot in it it sucks the gas. I have a 91 MJ 2wd 4.0/AX15 that gets 20 mpg or better. Just sips the gas.

I'm running ful width 60s, 38s, and a 4.0. I really like the motor. I would like to put a TF999 and an Atlas in it. If I kill the motor I may consider swapping in a chevy 4.3.

Originally posted by attachcurrie


What mods have you done and how much did it improve it?
My own is bone stock, I like it that way. But being surrounded by jeeps I've seen most of the usual gammit of mods - headers, K&Ns, etc - most of which seem to me to do very little.

BillaVista has a stroker, and while I'm impressed with the horsepower gain, I personally (no offense Bill) am unimpressed by the hassle required to get it, and get the motor running smoothly on pump gas. Just seems like you can get a lot more bolt on horsepower for SBC or Fords than Jeeps.

I'm not sure I would feel comfortable with Nos, turbo charging (too much change in tourque characteristics, which are primary plus to engine in first place), or supercharging, although I'm sure they would all result in dramatic gains in hp.

The length issue is a very good point, buddies 5.0 swap really cleared up some engine bay room!

My point of view is if you have a 4.0, keep it, and keep it stock. if you need more power, go SBC, but right now I personally don't need more power.

I say the 4.0 is a good motor it dosent weigh much but If your gonna have to swap put in a chevy TPI or TBI motor. :usa:

Just a thought , but smog? nobody has mentioned that. a 2.5 to a 4.0 in a wrangler is a legal swap with no hoops to jump through at the ref. station.
The 4.0 has repectable torque and i also get between 16 and 19 mpg.
all i'm sugesting is if you live out of state and your swapping in a engine that didn't come as an option for your ride you better do it right or have someone that will :zzz: while smoging it.

Not to far in the future of smog rugulations will clamp down even harder on that.


I'm a licienced smog tech and this is the advice that i give my freind s and anyone else who asks.


my .02

mike

Originally posted by The Rockslut
I was running 4:56 gears with 38.5" SX's and now have 5.13 gears with 39.5" TSL's.

Not sure of the exact mileage but it is around 20 mpg. Sucks more going up the freeway to the Con.

How are you getting 20 MPG with 5.13's and 38.5's? thats what I was getting when my rig was stock! now I get 15-16 mpg with 4.56's and 33" tsl radials. I think you need a new speedo gear dude.

Originally posted by SCORPION


How are you getting 20 MPG with 5.13's and 38.5's? thats what I was getting when my rig was stock! now I get 15-16 mpg with 4.56's and 33" tsl radials. I think you need a new speedo gear dude.

Sorry DUDE! DO you want to drive my rig and see what mileage it gets? First off i had 4.56's and 38's not 5.13's. So your junk sucks gas and mine doesnt. I drive my rig all the time and know what mileage it gets. I would now if my speedometer was off. I dont cruise down the highway in the slow lane with my speedo at 85mph and thinking i am getting geo metro gas mileage.

Besides I have another rig (if you would have read) that has a 4.0 and pulls down 20mpg around the city, even better on the highway. Wanna drive that one too? Wanna come check out my speedo gears? !:rolleyes:

I think you need to go away!

Factory Tubulars TJ that runs the UROC compitions still runs the 4.0
I am planning on keeping my TBI 4.2 in my scrambler for the UROC compitions next year....

A lot of people kepp the stock engines because you rarely need the full power of it anyways when crawling.

You brake stuff easy enough with the stock engine.

That is if you are crawling.

Muddin is different. :D

I still run a basically stock 4.0 in my rig. It's decent, torquey, doesn't burn oil, I always know it's gonna start (but I don't get close to 20 mpg):p

When I blow it up eventually, I'll replace it with a SBC or Ford. I probably wouldn't pay to go from a 2.5 to 4.0, though.
Dion

Wow - I'm kinda jealous. I'm lucky to get 14 MPG. Granted, I've got an auto with no overdrive, but even stock I was only getting 16. Oh, well, what do you expect when you're basically pushing a barn door through the air? :)

I made the choice to go with a 4.0 over a V8 for many reasons.
1. Had one before in an XJ, loved it very dependable
2. Length of drivetrain, as stated above. The 4.0 was a bolt in swap for my 4.2 a SBC would have made my driveshaft about 4" keeping the stock CJ-5 wheelbase of 84"
3. Cost by the end of my swap I will have only spent about a grand including the motor. Got it for $400.
4. Did anyone mention the fact that they run forEVER!
5. Last but not least. ITS A JEEP PRODUCT, and I like that.

And I actually kept it OBDII

Originally posted by The Rockslut


Sorry DUDE! DO you want to drive my rig and see what mileage it gets? First off i had 4.56's and 38's not 5.13's. So your junk sucks gas and mine doesnt. I drive my rig all the time and know what mileage it gets. I would now if my speedometer was off. I dont cruise down the highway in the slow lane with my speedo at 85mph and thinking i am getting geo metro gas mileage.

Besides I have another rig (if you would have read) that has a 4.0 and pulls down 20mpg around the city, even better on the highway. Wanna drive that one too? Wanna come check out my speedo gears? !:rolleyes:

I think you need to go away!

calm down slut! I just thought it was strange thats all.

Oh ya and you got the 39.5's and 5.13's not 38's and 4.56's, my bad.

Originally posted by SCORPION


calm down slut! I just thought it was strange thats all.

Oh ya and you got the 39.5's and 5.13's not 38's and 4.56's, my bad.

Its cool. I had a bad day that day :flipoff2:

Besides I lied. I get 19.5 mpg on average. :(

19.5 highway with 39's that great! We will be traveling from Texas to Colorado then to Moab this Fall so if I could pull that it would be awesome. What modifications to the engine do you have?

I have a Conical K&N on the end of a stock TJ intake tube. I have my exhaust running down the driver side that is 2.25" with a high flow cat and a 2 chanmber flowmaster. Thats it.

Can anyone else suggest any modifications that help with power?

Besides exhaust and K&N I never touched my 2.5L

What about a chip, wires, plugs, MSD, header? Any one recommend any of these.

I went ahead and bought the engine and will be swapping it in this weekend. Thanks guys!

RockSlut,
I am not at all familiar with your vehicle, but seeing that you’re running 39s, I would assume it’s a SWB Jeep. I’ve got ’02 TJ Sport, which while brand new never got more 16 MPG, and now that it’s at 10,000 miles, situation is not at all improving. It’s got 3.77s and 30s. While I understand, to a certain extent, about the break in periods of engines (mine) and the implied benefits that one can achieve with re-gearing in regards to the gas mileage...one seemingly small problem remains. Whatever it is you drive, being on 39s, it’s probably one of the least aerodynamic creations, and certainly less aerodynamic than a stock TJ. While I also realize that an application of a 4.0 is not most efficient in a TJ, I also can’t see your vehicle being a poster child for EPA. With all that said, RockSlut, I respectfully ask that you elaborate in more detail on what went into building/maintaining a 20 MPG 4.0, while taking into consideration the fact that the said 4.0 rolls on 39s

Thank You

Well there is that saying, YMMV - your mileage may vary.

Given that the original question was posed by someone comparing the 4.0 to a V8 swap, I think it is safe to say that the difference in gas mileage, either pro or con, would not in and of iself be enough to sway such a decision one way or the other.

Originally posted by JPrush
RockSlut,
I am not at all familiar with your vehicle, but seeing that you’re running 39s, I would assume it’s a SWB Jeep. I’ve got ’02 TJ Sport, which while brand new never got more 16 MPG, and now that it’s at 10,000 miles, situation is not at all improving. It’s got 3.77s and 30s. While I understand, to a certain extent, about the break in periods of engines (mine) and the implied benefits that one can achieve with re-gearing in regards to the gas mileage...one seemingly small problem remains. Whatever it is you drive, being on 39s, it’s probably one of the least aerodynamic creations, and certainly less aerodynamic than a stock TJ. While I also realize that an application of a 4.0 is not most efficient in a TJ, I also can’t see your vehicle being a poster child for EPA. With all that said, RockSlut, I respectfully ask that you elaborate in more detail on what went into building/maintaining a 20 MPG 4.0, while taking into consideration the fact that the said 4.0 rolls on 39s

Thank You


Sweet Jesus. Everything has been told that I have on my ride. Full width 94 YJ 4.0/999 (lockup converter HINT: lower RPM's although not overdrive) 5.13 gears 39.5" TSL's. I have a TJ intake tube and K&N, modified exhaust with 2 chamber flowmaster and high flow cat. THATS IT! I drive normally and the speedometer is correct. I dont drive around with my foot on the floorboard all the time and that is about the only way I could pull 19.5mpg. As soon as I floor it the gas gauge drops. Simple as that, and that is the same as any vehicle from a Geo Metro to a 502 big block.

Originally posted by The Rockslut


Sorry DUDE! DO you want to drive my rig and see what mileage it gets? First off i had 4.56's and 38's not 5.13's. So your junk sucks gas and mine doesnt. I drive my rig all the time and know what mileage it gets. I would now if my speedometer was off. I dont cruise down the highway in the slow lane with my speedo at 85mph and thinking i am getting geo metro gas mileage.

Besides I have another rig (if you would have read) that has a 4.0 and pulls down 20mpg around the city, even better on the highway. Wanna drive that one too? Wanna come check out my speedo gears? !:rolleyes:

I think you need to go away!

I'm glad someone gets good milage... Auto w/4.56 and 38's= about 14mpg on the HWY. This ia a 2000 TJ with 40,000 miles... Maybe it is not broke in!:eek:

I have gotten around 19 mpg with most of my carb'd 4.2's going slower (65, or less) on the freeway. As Rockslut said going down the freeway to the trail, he got much worse. I got much worse following my buddies with V8's to the trail. In fact when we gassed up the the 360 used one more gallon than the 4.2 did in one tank's worth of gas.

I went from 4.0L to TBI 350 in my 91 YJ. The biggest difference is the ability for the TBI 350 to lug down. I can easily lug it down to 400 RPM with no problem. My old 4.0 would either die or the ECM would kick the RPM's up to 1k for a second to keep it from dying. The RPM kick was the biggest PITA. I was running 125:1 with my 4.0L and 130:1 with the 350 so the difference between the two is all motor. I would never go back to the 4.0. As far as the "to much power" power thing goes. I gaurantee you that a stock TBI 350 isn't going to have "to much power".

In CA, if you go from 4cyl to 4.0 in a jeep you still have to go to the ref.

I have no clue what the mpg difference is, but I suspect it is fairly close to the 14 I was getting with the 4.0. My YJ is a trailer queen so I could care less about mpg anyway.

Originally posted by The Rockslut



Sweet Jesus. Everything has been told that I have on my ride. Full width 94 YJ 4.0/999 (lockup converter HINT: lower RPM's although not overdrive) 5.13 gears 39.5" TSL's. I have a TJ intake tube and K&N, modified exhaust with 2 chamber flowmaster and high flow cat. THATS IT! I drive normally and the speedometer is correct. I dont drive around with my foot on the floorboard all the time and that is about the only way I could pull 19.5mpg. As soon as I floor it the gas gauge drops. Simple as that, and that is the same as any vehicle from a Geo Metro to a 502 big block.


OK, so I find it odd myself being how I have managed to log in well over 100,000 miles on my 91 4.0 with everything from bone stock to what it is now. With all terrain 35's and 4.56 I could get in the upper teens easily with header, K&N intake, no CAT, 2 chamber Flowmaster, modified timing, MAP modifier, and Crane ignition and the most important for mileage and crawling,.........an electic fan. However I ran very lean!!!!! I ended up puting every dang aftermarket cooling product in the world and it just didnt cut it when running the A/C or in hard climbs. I then went to Dana 60's, an Atlas II, 38.5 SX's, 5.13's........my gas mileage dropped just under 15 around town and with me running on way too much air pressure for the life of the tire or good ride characteristics. All that and I was still running lean,......couldnt pass emissions to save my life and would run hot on long hill climbs. I then went to an adjustable fuel pressure regulator and am now down in the 12-13 range around town running about 15psi in the tires and I could still use more fuel for proper rich lean mixture. Anyone that does an air filter and exhaust must increase their fuel input as the 4.0 tends to almost want to run lean, it makes for good power and gas mileage, but detrimental everywhere else.

As for the 4.0 making a good crawler or not, I love it and with it having been hydrolocked twice and still thumping at 190,000 miles(100,000 of that lifted) its almost impressive and will almost surely rebuild it in lieu of swapping. I did however trash the AX15 and would recommend putting an NV3550 in for a good easy swap with no major hassles and its been real tough so far.

for whatever my .02 is worth,................

well my yj must be on crack. I run nothing but 87 octane and I it smogged with barely readable emissions. The smog dude said that he has never seen a 4.0 run that clean. HUH?

Guess it sucks to be you guys :flipoff2:

Originally posted by The Rockslut
well my yj must be on crack. I run nothing but 87 octane and I it smogged with barely readable emissions. The smog dude said that he has never seen a 4.0 run that clean. HUH?

Guess it sucks to be you guys :flipoff2:

You should show it to a DC engineer so they to can learn the secret of good fuel ecconomy. :flipoff2:

what are you running for a speedometer gear? I am guessing it should be a 34 oe 35 tooth if it came with 3.07's stock. If it didnt come with 3.07's than what did it have?:question:

Just trying to think this through......peace:flipoff2:

I cant remember what gear came from the factory. I had an auto so I had 3.55 gears. I have swapped the gears a couple of times trying to get the speedo correct. I have changed tire size and gear ratio's a couple times so I keep having to change it. Maybe the 35 tooth gear. Not sure though. My fuel mileage was horrible with the 36" SX's and 4.56 gears. I was undergeared and constantly on the throttle. The 38's and 4.56s actually helped on the freeway because it would plane out like a boat does. Once up to speed it just putted along.

Not to call BS- but I've never gotten 20mpg... or know any one out here in AZ who has eather- would be nice. ideas anyone???

When all was stock 4.0 5spd 31x10.5s or later 33 12.5s. now heavier d44 w/456s. I can now use 5th gear (something new and never before used) but I empty a tank in no time flat. Normal was 14-16mpg if keeping my foot light. Will be looking for 36's or 37's to put it back in rpm/spedo range.

I like the 4.0 no plans to change, normal issue is you will need to replace the rear main seal- factory one will leak.

I not only think, but wish that "The Rockslut", would start working for DC. He seems to have "mastered" fuel economy in his rig!!!

Boy this in nice to read that someone has mastered the technique to be able to defy all other means for mileage. I'll bet that these claims are well documented somewhere in his jeep diary too!!

Maybe he'll share them someday, unless they are being with-held in a "time capsule".

95 YJ running a 4.0l with 60/44, Atlas, NV4500 5:38's in the pumpkins on 37's. Performs real good crawling, really don't run the mud or sand much. I don't worry about the mileage, just fill it up when it's empty... not even sure what speedo gears to go with anyway. Often thought about 350 or LT1, just not sure if it's worth all the hassle of the swap. Maybe stroke the 4.0l instead.

i have to agree with (chadloyd).i got a 4.3 5speed in my my 84 cherokee..and a 4.0 auto in my 90..i seem to find that the 4.3 is way better on gas than my 4.0...4.0's are hogs om gas
:smokin:

Originally posted by Jeepmangled87
I say the 4.0 is a good motor it dosent weigh much but If your gonna have to swap put in a chevy TPI or TBI motor. :usa:


What? The 4.0 is extremely heavy for it's displacement. It weighs more than most v8s out there. It's a good motor and should has great torque at low rpm, which is perfect for crawling. It's no v8 though obviously.