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Discussion Starter · #1 ·
The new October Peterson 4wheel mag came in the mail today and has a article on putting the little Cummins in aTJ

They used both the Cummins flywheel then a spacer then the 4.0 TJ flywheel and made a tranny adapter to move the stock 4.0 5 SPd bell back a similar amount

They also used a PT cruiser intercooler

limited info but worth a read




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Discussion Starter · #3 ·
Don't know about longevity but HP torque match up nicely to the old reliable Ford 300/4.9 with Cummins being smaller and a extended flat torque curve
But it lacks the inherent balance of a straight six so wonder if it is a 300k mile engine like the Ford


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I want to replace the 2.5L/ax5 in my YJ, with one of these and an ax15
 

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Sounds like a shade tree mechanic way of doing something.
Now you have an even shorter drive shaft and increased U-joint angles.

No thanks.
 

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Discussion Starter · #8 ·
Given that the diesel is only about 2 feet long 25.1 inches) you can move it forward to more then make up a couple inches of adapter


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the thing I don't get with these, is that Cummins seems to concentrate on replacing the 4.0 liter with this kit..

and that doesn't make any sense to me...why ignore the obvious...the 2.5L owners who would want the added power more than the 4.0L owners would, since most 4.0L guys seem happy with the six cylinders power

..I know I'm happier driving my 4.0L TJ on the highway than I am my 2.5L YJ

in fact, if the R2.8 was available as a bolt in replacement kit for the 2.5L (which seems like the motor mounts would be easier to do than on the six), I would order an ax15 and a R2.8 today
 

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Discussion Starter · #10 ·
The article I referenced in original post is replacing a 2.5 in a 1997 TJ


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Did that article happen to mention the total cost of the conversion?

Have read articles and different forum threads on that Cummins swap never any mention of total cost. My feeling is it will be close to 10 grand with the purchaser doing most of the work, that is just a guess. If it is that much I would say not to many would really be that interested in a 4 banger diesel. When a v8 conversion or even a 4.0 conversion for the SE's would be about the same cost or less. Seeing how parts availability nationwide would be much better with the v8 or 4.0 conversions.

One article did mention a composite oil pan on that 2.8 that is less than desirable offroad. They reported the reason for the composite oil pan was for noise reduction in the lower end.
 

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Discussion Starter · #12 ·
Yep they said kit price estimate was 8-10k and that did not include adapters or install or intercooler (so yep real pricey)

They also said they cracked the oil pan and a skid or metal pan was strongly recommended


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Yeah for that kind of money when the 2.5 in mine takes a dump I'll either do a 4.0 or just another 2.5. As it works well enough for the type of wheeling and road work it gets.
 

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Yep they said kit price estimate was 8-10k and that did not include adapters or install or intercooler (so yep real pricey)

They also said they cracked the oil pan and a skid or metal pan was strongly recommended


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Who's they? Cummins still hasn't released any pricing information. Last update email I got from them was a survey. Nothing but speculation at this point.

Cummins has updated their website though with a gear ratio calculator for the R2.8. Looks like any gearing for the 4.0 will work with the R2.8. AKA, redline looks like it might be the same. So while maybe not the most ideal gearing for the R2.8, those of us over geared wouldn't have to re-gear.

https://cumminsengines.com/repower.aspx#sectionCalculator

Oil pan material is irrelevant. You should be protecting it with a skid plate anyway.
 

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Discussion Starter · #15 ·
First line of first post identifies where info was found and they said it was estimate they got from Cummins

I am not seeing it as a great advantage more of a conservation piece as I don't think a four will have the longevity of a straight six and price is prohibitive as will be repairability and parts availability

Basically the power and torque curve of a 300/4.9 gas Ford straight six with less longevity with a jump in mpg offset by price of engine and price of diesel fuel




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Here's the thing on MPG gain.....How long will it take to recoup the cost of the swap in fuel savings?.... Without putting pencil to paper because individual results will vary. It would take more years than I care to think about.

EGR systems are notorious for failures and expensive to repair, not sure what the engine-mounted passive diesel oxidation catalyst is. If it's anything like a Diesel Particulate Filter then that's another expensive item to replace when it dies.

When
the intercooler gets a hole in it (and it will eventually) especially on the trail you'll be sucking dirt infused air into the intake. Might as well take a sand blaster to the internals.

Unless Cummins has found a way for the turbo to spool up very early in the throttle position that motor won't have near the power as a gas motor when crawling.

IMO if you want that 2.8 motor bad enough and have the money to blow go for it.
If you want a tried and true engine with easy access to parts nationwide, including that parts house or junkyard closest to the trail you just got stranded on then stick with the 2.5, 4.0, or v8 conversion.
 

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Good luck getting that to pass smog in cali for 8-10k Lol. Probably be closer to 20k once you got it to pass in Cali. Better off going with a golen stroker at that point.
 

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Here's the thing on MPG gain.....How long will it take to recoup the cost of the swap in fuel savings?.... Without putting pencil to paper because individual results will vary. It would take more years than I care to think about.

EGR systems are notorious for failures and expensive to repair, not sure what the engine-mounted passive diesel oxidation catalyst is. If it's anything like a Diesel Particulate Filter then that's another expensive item to replace when it dies.

When the intercooler gets a hole in it (and it will eventually) especially on the trail you'll be sucking dirt infused air into the intake. Might as well take a sand blaster to the internals.

Unless Cummins has found a way for the turbo to spool up very early in the throttle position that motor won't have near the power as a gas motor when crawling.

IMO if you want that 2.8 motor bad enough and have the money to blow go for it.
If you want a tried and true engine with easy access to parts nationwide, including that parts house or junkyard closest to the trail you just got stranded on then stick with the 2.5, 4.0, or v8 conversion.
Not everyone is in this for more power. Even then, it's a Cummins so there's likely a lot of hidden power waiting to be released. Not everyone is in this to get their money's worth. Sure it's probably going to be a big investment but I've never seen any swap truly get their money's worth. People do it because it makes them happy so let some people be happy. That being said, you are easily doubling your average mpg so if you daily your TJ this will pay for itself. Likely still cheaper than buying a fuel efficient commuter unless you want a really cheap beater.

Also the Cummins 2.8 is already a tried and true engine. Been used in other countries for several years now. One of the main reasons Cummins selected this engine to make a crate kit for
 

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Good luck getting that to pass smog in cali for 8-10k Lol. Probably be closer to 20k once you got it to pass in Cali. Better off going with a golen stroker at that point.
Cummins already has the engine compliant in all 50 states last I heard
 

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Discussion Starter · #20 ·
They have numbers and mpg is not double more like 40% more
And they are still working on emissions completion because of calif

You do get more noise and much more vibration


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