Well i'll definitely will stay tuned for this build sir, Id like to r2.8 swap my Lj considering the cost of the plan i have to build a 4.7 Stroker that can handle boost, but realistically thinking id rather have something fuel efficient like the r2.8 that has some torque to "push" all the additional weight from mods, And something more fuel efficient would be great since it is my daily that's driven 80+ miles a day! Plus the cool factor of having something swapped is badass to me
Id love to hear some Mpg numbers my man and how it drives once your done with this project !
R2.8 in TJs tend to get anywhere from high teens mpg to low 30s mpg, but I would say most guys that have build mostly for off-road use will get mid to low 20s. When I first finished my swap I was getting 26 mpg mixed and I was driving the Jeep very easy, but still with KM3 tires 33 x 10.5" with 3.07s and AX-15. Running a more aggressive mud tire before the swap I was getting 11 mpg, but that really had a lot to do with the tires and the gearing, because I could swap tires and get 18 mpg, but the experience was miserable either way IMO compared to my ZJ with a V8.
Turbo diesel engines also have A LOT of unused potential in regards to tuning and they come regulated from that factory where power, reliability, and MPG are close to last on how they are tuned. Almost every single mod you do you're going to see in your fuel logs if you keep them.
The R2.8 IMO is not a quick engine in a TJ, but it's very similar to the 4.0 until you get to highway speeds where it will actually maintain speed without a lot of shifting. But it slowly accelerates. I have driven mine and not noticed but after cresting a hill I'm doing 90 because I didn't notice I was speeding up. That's just the nature of a 160ish HP diesel engine. If it was 300 hp you'd really feel the throttle response and you'd still get basically the same MPG.
I've found MPG only to matter in the fact that I don't have to worry about fuel all the time. And if you are worrying about fuel, you don't need as much and it's much easier to store and fill compared to gas which is so volatile and always trying to make its escape and burn the place down. You're very unlikely to ever "pay" for a build either based on MPG, though there would be a slight possibility of this in other countries that have less regulations. Though in those countries you wouldn't need to do a swap anyway, you'd just buy whatever you wanted from the OEM for a fraction of the cost of US vehicles.
But my biggest preference for diesel for a vehicle like a Jeep or truck is the low end and steady torque curve. Even gas V8s don't have enough low end torque and the torque response is kinda "spikey" so you either need weird gear ratios keeping the engine screaming which I really don't like on long highway trips and hurts the MPG more or you deal with constantly shifting, which is harder to get right for the DIY engine swap (though there's a bunch of options where this is probably not as big of deal if you're looking at say a LS swap or something common) and it's hard on transmissions too and annoying for guys with manual transmissions. Basically I always find that even the big V8 engines always want to accelerate (slow down or speed up) and not just maintain speed.
I do need to give the OEMs some props making the gas (unfortunately a lot of the new diesels too) powered trucks and Jeeps ie turd sandwiches taste so good (it's regulations and not the fault of the OEMs). It's incredible the amount of infrastructure and the amount of engineering and marketing to make all these gas powered vehicles palatable, but they aren't that bad, unless you get used to not eating the turd sandwich and then you're always noticing the turd in the sandwich.
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