2.5L upgrade...

YJ103

YJ103

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This may seem like a dumb question, but I'm just thinking outside the box for when someday my YJ needs a heart transplant. Why does no one ever try to install a hopped up 4cyl? With all the hi performance 4 bangers out there, it would seem that one could be adapted to fit. Chevy 350s and the 4.0 seem like common transplants but seem to need the replacement of all sorts of extraneous parts to handle the added HP.

Has anyone seen or heard of a built jeep 2.5L?
 
Plan on including a different transmission if you have the 5 speed AX-5 because it can't handle any added power. I'm not sure about the automatic transmissions with the 2.5L
 
Flyer58 said:
Plan on including a different transmission if you have the 5 speed AX-5 because it can't handle any added power. I'm not sure about the automatic transmissions with the 2.5L
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I assumed a tranny swap with a new engine, I was thinking more along the lines of all the other stuff. I imagine a larger radiator, heavier springs, sometimes a new rear end- things like that that may not need to be changed out. For instance Chevy makes a 200hp 2.5L and if you could make that work, it would be a nice little upgrade. I'm just curious why no one goes a route like that.
 
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Well it's possible, and worth it if you have the $ or the talent.
I put a 175hp Hot-Rod 2.0 Pinto mill in my old '43 GPW many years ago.
But it took a Lot of fabricating, including a bell housing for the Chevy SM420 tranny I wanted (and still do).
But that little Hot-Rod motor was Everything I ever could have wanted, or needed.
When it's all said and done though Jeeps really come down to Gears, lower the better, at least for OR performance.
 
My guess as to the reason why no one does this is because it doesn't really make sense to. If you have to convert your whole engine and engine management to another engine, why would you go with a slightly stronger 4 cylinder? Most 4 cylinders, even modern, are still not as powerful as the Jeep 4.0 and certainly not a V8, unless they have a turbo slapped on them. Assuming the GM engine you are talking about is the Ecotec 2.5L, which is 190hp and 171 ft lbs of torque. Haven't seen the dyno on that torque curve but my guess is you have to rev it way high to get any of that power seeing as it's a DOHC engine. And 171 ft lbs is not really all that much power, certainly not worth doing a custom setup for, especially when the rest of the world hasn't done it so you would be the guy figuring everything out.

On the other hand, you can get an immediate huge power increase with the 4.0 (roughly 220 ft lbs of torque and it's down low) and it's really not that hard to swap to especially since it was an OEM setup. Collect all the parts, weld on new frame mounts, and you're basically good to go. If you're going custom swapped engine, then you may as well go with a V8 to maximize your power return after you invested so much into it.

I have seen a few people "build" the Jeep 2.5, I have never seen any good results come from it. I've pretty much only seen eBay turbos or the 505 performance stroker. Neither with great reviews and based on their accel videos, I am certain my regeared 4.0 would still smoke them.

If you don't need a ton of power, then just regear the 2.5 appropriately and drive it as is. If you want more power beyond that, swap the 4.0 if you want something easy, or reward yourself with a V8. Don't bother with a bunch of time on another 4cyl solution. My thoughts, anyways.

Not trying to be a downer, but going with a different 4 cylinder makes no sense to me when I look at the logistics of it. Better off keeping what you have and gearing it appropriately, or swap to one of the more popular, much more powerful options, IMO.
 
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machoheadgames said:
My guess as to the reason why no one does this is because it doesn't really make sense to. If you have to convert your whole engine and engine management to another engine, why would you go with a slightly stronger 4 cylinder? Most 4 cylinders, even modern, are still not as powerful as the Jeep 4.0 and certainly not a V8, unless they have a turbo slapped on them. Assuming the GM engine you are talking about is the Ecotec 2.5L, which is 190hp and 171 ft lbs of torque. Haven't seen the dyno on that torque curve but my guess is you have to rev it way high to get any of that power seeing as it's a DOHC engine. And 171 ft lbs is not really all that much power, certainly not worth doing a custom setup for, especially when the rest of the world hasn't done it so you would be the guy figuring everything out.

On the other hand, you can get an immediate huge power increase with the 4.0 (roughly 220 ft lbs of torque and it's down low) and it's really not that hard to swap to especially since it was an OEM setup. Collect all the parts, weld on new frame mounts, and you're basically good to go. If you're going custom swapped engine, then you may as well go with a V8 to maximize your power return after you invested so much into it.

I have seen a few people "build" the Jeep 2.5, I have never seen any good results come from it. I've pretty much only seen eBay turbos or the 505 performance stroker. Neither with great reviews and based on their accel videos, I am certain my regeared 4.0 would still smoke them.

If you don't need a ton of power, then just regear the 2.5 appropriately and drive it as is. If you want more power beyond that, swap the 4.0 if you want something easy, or reward yourself with a V8. Don't bother with a bunch of time on another 4cyl solution. My thoughts, anyways.

Not trying to be a downer, but going with a different 4 cylinder makes no sense to me when I look at the logistics of it. Better off keeping what you have and gearing it appropriately, or swap to one of the more popular, much more powerful options, IMO.
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Good point on the engine management system.

And you and I keep saying it, Gears, Gears, Gears...

I was actually going put 215 Buick in the flatty but the yards wanted outrageous $.
 
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jeepjoe43 said:
Good point on the engine management system.

And you and I keep saying it, Gears, Gears, Gears...

I was actually going put 215 Buick in the flatty but the yards wanted outrageous $.
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Gears are hands down the best mod you can do in my mind. You can keep adding power all you want but if the output is choked at the axles, more power doesn't do all that much. On the other hand, the gears will allow you to unleash the power on practically anything which is great and on a powerful engine, just amazing.

I actually regeared my truck 2 days ago. 6 speed manny, 31.5" stock tires, went from 3.692 to 4.56. Holy cow, so much better. People swear I'm crazy to run 4.56 on stock tires, but I know better. It is awesome to say the least. Highway cruising 70 at 2700 rpm. And it has 260hp/280tq, so it's not like it's a slouch to begin with. Still, it likes gears. Getting about 18 mpg on the hwy, which is about the same as it got stock at 2100 rpm. Except now I don't have to downshift when a butterfly hits the windshield.
 
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The more I read, the more you people keep talking me into 4.88's in my 2.5L, AX-5, with 31's
It's ok now for grocery shopping on flat roads but highway speeds 60+ and any hill maxes it out.
 
Flyer58 said:
The more I read, the more you people keep talking me into 4.88's in my 2.5L, AX-5, with 31's
It's ok now for grocery shopping on flat roads but highway speeds 60+ and any hill maxes it out.
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4.88 and 31's would be great on the 2.5. Don't want to spend your money, but I very rarely see someone regret making that change.
 
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machoheadgames said:
Gears are hands down the best mod you can do in my mind. You can keep adding power all you want but if the output is choked at the axles, more power doesn't do all that much. On the other hand, the gears will allow you to unleash the power on practically anything which is great and on a powerful engine, just amazing.

I actually regeared my truck 2 days ago. 6 speed manny, 31.5" stock tires, went from 3.692 to 4.56. Holy cow, so much better. People swear I'm crazy to run 4.56 on stock tires, but I know better. It is awesome to say the least. Highway cruising 70 at 2700 rpm. And it has 260hp/280tq, so it's not like it's a slouch to begin with. Still, it likes gears. Getting about 18 mpg on the hwy, which is about the same as it got stock at 2100 rpm. Except now I don't have to downshift when a butterfly hits the windshield.
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Nice!
 
I told you it was a dumb question. ;) Since I rarley ever do anything with my jeep other than drive it around town and to the beach, it looks like I may just keep the little 4 popper and regear for my 31's when the time comes. It would be nice to travel in the passing lane once in a while...
 
YJ103 said:
I told you it was a dumb question. ;) Since I rarley ever do anything with my jeep other than drive it around town and to the beach, it looks like I may just keep the little 4 popper and regear for my 31's when the time comes. It would be nice to travel in the passing lane once in a while...
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The only dumb question is the one unasked friend!
 
Stoopid Jeep said:
4.88's and 31's, it still isn't fast.
It has no problem jumping on the freeway at 70mph, even on the uphill on-ramps.
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I have 4:10 with 31’s and 55 is difficult to get to at the on ramp of the freeway. I guess it must make that much of a difference huh? I never use 5th either.
 
gixxerkid3 said:
I have 4:10 with 31’s and 55 is difficult to get to at the on ramp of the freeway. I guess it must make that much of a difference huh? I never use 5th either.
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It will never make a slow engine “fast” (4.0 included) but it definitely lets them open up their potential. Have to remember that Jeep sized the tires on these rigs with 27’s and street tires at that, so 31’s is like a 13-14% torque reduction by leverage alone, not to mention weight, especially once you get into the heavier aspects of all terrains or mud terrains. Do all that to a stock 4 cyl and it’s a big drain.

For me it makes the 4.0 good enough that I probably won’t ever bother to add any sort of power to it via V8 or stroker. Hard for me to speak on the 2.5 but I know in principle what works well because that engine likes rpm so I typically take what I like on the 4.0 and recommend one ratio lower for the 2.5. The 2.5 AX5 has a lower 5th ratio than the 4.0 AX15, so going one ratio deeper in the 2.5 is basically on the highway, about 2 gear ratios lower. This keeps the 2 engines in rpm ranges they like to work in.

Put another way, 4.88/31 would be similar to stock. Maybe a teensy bit higher rpm than stock was which helps make up for the heavier 31” tire and if anything, it’s not like stock was the perfect ratio to begin with so it adds back some zip you never had. Good upgrade all around. Not using 5th is a pretty normal solution for the tires you have on that ratio.
 
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