Can you bore/stroke a 2.5L engine?

[Wow]

I'm thinking about building a super light older XJ with stock tires and a 5 speed with a 2.5L engine for good gas mileage as a commuter. I know the engine is based on a 4.2L minus the middle 2 cylinders. I wonder if it could be possible to cut down a 4.2L crank and make a standard 4.0 type stroker? How much larger can it be overbored?

Aside from that...super/turbo charger? How hard would it be to match the six's performance with a 4 cylinder?

PS - is the 4 cylinder engine more or less the same from 1984 to 1996 or even later?

 

[5-90]

Forced induction would be the better bet. While the 150ci I4 is "part of the AMC I6 family" in a distant way, there's not enough parts commonality to make a stroker work - that I know of. It would take one-off parts or parts that happened to fit something else instead.

The most difficult part would be the crankshaft, since offset grinding the crank would be the more effective (and probably more reliable) way to get it done than trying to cut/weld/twist the I6 crank (the I6 crank has throws every 120*, while the I4 crank has throws every 180*. It's not a simple cut-and-weld, unless you're going to do it a cylinder at a time. And, I'm not sure if the journal measurements will support the idea.)

 

[PhotographerMike]

I'm thinking about building a super light older XJ with stock tires and a 5 speed with a 2.5L engine for good gas mileage as a commuter.

We have a stock '96 2 door, 2 cyl., 5 speed, SE (minimal options). Before I added factory skids, hitch and stuff the weight was right at 2800 lbs. With the factory axle ratio of 4.11 the engine is turning quite a bit faster than our heavier, well optioned 4x4 '89 with auto. trans. and 3.55 gears, so the mileage isn't that much better in the "little" 4 cyl.

For better street mileage, IMO. go to taller than stock 215/75 (235/75 x 15 would work) "high mileage" tires, remove the roof rack cross pieces, keep the under bumper air dam and maybe add a factory front skid to smooth the air flow. Keep the speed of the "brick" down, with 4.11 gears, you might want to.

I've never had problems with lack of power unless we're heading up a long hill carrying an extra 4 or 5 hundred pounds on vacation. Again, IMO, if you mod. the 4 cyl. to have the power of a 6, you'll have the same, or less gas mileage of a similarly configured 6.

 

[CherBear]

I would go forced induction as well for a few reasons:
Strokers create torque which is great for off road, low rpm situations. A turbo will give you lots more power in the higher RPMs, which would be much more usable as a commuter.

Also as 5-90 said. The parts just really aren't there. The amount of custom work would be staggering if not outright impossible to build a stroker.

Jeep Cherokees and Mpg don't go together all that well.

 

[djblade311]

why bore and stroke a 2.5? Just swap to a 4.0L. If gas mileage is a big concern that requires you to dump time and money, but an old Honda commuter car.

 

[5-90]

I would go forced induction as well for a few reasons:
Strokers create torque which is great for off road, low rpm situations. A turbo will give you lots more power in the higher RPMs, which would be much more usable as a commuter.

Also as 5-90 said. The parts just really aren't there. The amount of custom work would be staggering if not outright impossible to build a stroker.

Jeep Cherokees and Mpg don't go together all that well.

Turbocharging gives you increased output at high crankshaft speeds, but you have to select parts (particuarly the turbine!) carefully to prevent turbo lag and "running out of boost" at the other end of the problem.

Supercharging is better for low-RPM torque, and that's where the AMC/Jeep engines tend to excel. A supercharger is also a "string-driven thing," and compressor output is directly tied to crankshaft speed (which means no lag.)

Either system has its advantages, so select according to what you want to do.

 

[Ghost]

why bore and stroke a 2.5? Just swap to a 4.0L. If gas mileage is a big concern that requires you to dump time and money, but an old Honda commuter car.

Not all xj's can easily accomadate that philosiphy. You can bore it, cam it, and run a 4.0L TB for starters. I ran a 4 popper in my 84 for 5 years and looked for a way to stroke it. Only option I ever found was offset grind the crank. Now their is a Mopar performance engine that uses a Hemi head that can be built to anything from 2.0L to 3.0L iirc. Never was able to find out what transmission bolt pattern the little motor had though.

 

[KRAKER]

I've considered this setup. It's lightweight, cheap, and has decent reliability. For most wheeling you don't really need that much power. Atleast the wheeling I do. But every once and a while you need just a lil more power to get up the hill, rock e.t.c.. A balls to the wall four banger would cost a mint. It will still be gutless and be nowhere near the desireable powerband and curve that the I6 4.0 has. forced induction would be best in the form of a supercharger. Which would be way too much coin for me to spend.

Nitrous would be the a good alternative. You would have cheap, stable, predicatable power on demand. The lightweight benefits of the fourbanger at an affordable price tag. Plus you will still have the good mileage. The stock 2.5 in sound mechanical shape could easily take a 100 shot. You could even stage the setup so you don't get a sudden burst of power and start snapping parts. You must still build your drivetrain accordingly. If I were to suddenly unload the drivetrain while squeezing the motor would probably go BOOM! There are ways to control a squeeze setup but with any mod there are risks.

 

[Ghost]

I've considered this setup. It's lightweight, cheap, and has decent reliability. For most wheeling you don't really need that much power. Atleast the wheeling I do. But every once and a while you need just a lil more power to get up the hill, rock e.t.c.. A balls to the wall four banger would cost a mint. It will still be gutless and be nowhere near the desireable powerband and curve that the I6 4.0 has. forced induction would be best in the form of a supercharger. Which would be way too much coin for me to spend.

Nitrous would be the a good alternative. You would have cheap, stable, predicatable power on demand. The lightweight benefits of the fourbanger at an affordable price tag. Plus you will still have the good mileage. The stock 2.5 in sound mechanical shape could easily take a 100 shot. You could even stage the setup so you don't get a sudden burst of power and start snapping parts. You must still build your drivetrain accordingly. If I were to suddenly unload the drivetrain while squeezing the motor would probably go BOOM! There are ways to control a squeeze setup but with any mod there are risks.

Drivetrain is not that big of a deal. Just put a Dakota housing on a ax-15 and drop it in and you should be good for no matter what you do to the 4 popper.

 

[Johnnie Walker]

LSx/GM truck motor FTW! With proper gearing, you have great power and decent mileage. If you run 2wd, you can toss in a T-56 while you are there.

 

[KRAKER]

I wouldn't contest that. I've "heard" of people getting 20 mpg with SBC swaps. But it doesn't do much for weight savings.