High Fuel Economy Engine Swap Options?

[Oyaji]

Let me preface this by saying straight at the outset that I am unsure whether I will ever get around to actually doing this...

.

I'd like to come up with an engine swap for a Comanche that would offer reasonable torque (say in the range of 2.5 to 4.0 liter performance), but at significantly better fuel economy than either of those stock engines. Said swap option should not be terribly complicated, and target fuel economy would be 25+ MPG. Because they are inherently balanced by design, I'd prefer an inline-6 - and one with 7 main bearings at that, but realistically I fear that is out of the question. Said engine should be available from junkyards - low price and high numbers available would both be pluses. Weight should be no more than the stock weight of the 4.0 + 10% (~600 pounds) - less weight would be an advantage. For gasoline engines, some sort of variable valve timing is highly desirable, and fuel injection mandatory. For diesels, mechanical injection is preferable to reduce complexity inherent in the wiring of CRDs.

.

Some ideas I have kicked around are the 2.1 Renault and VM 2.5 diesels (easy swaps, but parts hard to source), and the Mercedes Benz OM 617 5-cylinder. The Cummins 4BT swap is just too damn heavy, and so is beyond consideration. I have seen a site that showed a 2.8L CRD swap, but it looked overly complex (though I suppose transmission and transfer case swap along with the engine might make this worthwhile?). How about gasoline options - any ideas?

.

Just approach this as a thought experiment, and feel free to pitch out your ideas for critique and discussion - thanks guys.

[Eagle]

I think your solution is a lot closer than you realize. Pre-ethanol, when my '88 Cherokee was still relatively new, running on the original P205/75R15 tires and with a 5-speed through the stock 3.07 gears, I got as high as 28 MPG highway and overall average was probably in the low to mid-20s.

 

I'm not at all sure what range the factory optimized the 4.0L cam for, but I can't help thinking that a "torquer" or "RV" cam installed to optimize torque and horsepower at the low end of the RPM range would easily deliver 25 MPG -- even with 10% ethanol. Driving 5-speeds, my normal shift point is 2,200 to 2,500 RPM and highway cruise is under 2,000 RPM. Even with the automatic in my wife's XJ, highway cruise is only 2,200 to 2,300 RPM. Pick a cam grind that's optimized for the 2,000 to 3,000 RPM range rather than 4,000 to 5,000 RPM, and you should be well on your way.

[Oyaji]

I think your solution is a lot closer than you realize. Pre-ethanol, when my '88 Cherokee was still relatively new, running on the original P205/75R15 tires and with a 5-speed through the stock 3.07 gears, I got as high as 28 MPG highway and overall average was probably in the low to mid-20s.

 

I'm not at all sure what range the factory optimized the 4.0L cam for, but I can't help thinking that a "torquer" or "RV" cam installed to optimize torque and horsepower at the low end of the RPM range would easily deliver 25 MPG -- even with 10% ethanol. Driving 5-speeds, my normal shift point is 2,200 to 2,500 RPM and highway cruise is under 2,000 RPM. Even with the automatic in my wife's XJ, highway cruise is only 2,200 to 2,300 RPM. Pick a cam grind that's optimized for the 2,000 to 3,000 RPM range rather than 4,000 to 5,000 RPM, and you should be well on your way.

.

Now there is a thought!    Dropping the peak torque RPM would allow re-gearing/taller tires and add efficiency at cruise speed. Over 100,000 miles the best I have been able to squeeze out of my  all stock 92 XJ was 22.5 MPG highway at 50-55 MPH, but more generally 20.5 MPG at 65 MPH. The jump from 20 to 25+ MPG is quite a big one, but the jump from 20 to 30 MPG  would be    enormous...  yet achievable with a diesel, I think. What I am after is the biggest gain attainable with an engine swap/modifications.

.

I still can't get past the thought that a more modern engine with 1) overhead cam(s) 2) variable valve timing and 3) significantly lighter weight would get me even better economy, so I am curious to explore  alternate engine options  further.

.

Still,  changing the camshaft may well be the best, simplest, and cheapest option. Does anyone have any recommendations on manufacturers and cam grinds?

[GirsMJ86]

:agree:  with Eagle

 

My '91 Eliminator 4.0L Auto 4x4 got 25mpg highway, so what you're wanting would totally be do-able with the 4.0L and a low rpm cam like Eagle said. That rig was not stock either, bet it would have done better if it was. I did run 91 octane though most of the time, and it was a Jasper motor with relatively low miles for the vehicle age.

 

A diesel swap would the best thing for top mileage, and is something I've thought about plenty. The main problem seems to be though the weight of the diesel blocks that will fit our rigs, plus the uniframe needs to be reinforced. A diesel swap is much more something to do to a J-Truck than our little MJs IMO. That is to go with a modern block that actually makes the swap worth it to me.

 

I know next to nothing about this so I'm just kind of tossing this out here. Have you looked at propane conversion? Not sure if that nets any amazing mileage or not, or if it's even worth the cost, but that's another option if it is.

[Oyaji]

:agree: with Eagle

 

My '91 Eliminator 4.0L Auto 4x4 got 25mpg highway, so what you're wanting would totally be do-able with the 4.0L and a low rpm cam like Eagle said. That rig was not stock either, bet it would have done better if it was. I did run 91 octane though most of the time, and it was a Jasper motor with relatively low miles for the vehicle age.

 

A diesel swap would the best thing for top mileage, and is something I've thought about plenty. The main problem seems to be though the weight of the diesel blocks that will fit our rigs, plus the uniframe needs to be reinforced. A diesel swap is much more something to do to a J-Truck than our little MJs IMO. That is to go with a modern block that actually makes the swap worth it to me.

 

I know next to nothing about this so I'm just kind of tossing this out here. Have you looked at propane conversion? Not sure if that nets any amazing mileage or not, or if it's even worth the cost, but that's another option if it is.

.

I had no idea that sort of economy was possible with a 4.0. I am not familiar with the Jasper motors - are they strokers that use the old carburetted-6 crankshafts? I can see how that would add bottom-end grunt...

.

Since you have put thought into them, let's talk more about diesels. Provided the torque and weight of the new engine are kept in the ballpark of the 4.0's, I don't see how frame strengthening is required. What engines have you considered? Automan has suggested that with careful driving he might well be able to better his Renault 2.1 TD's 30 MPG to 35 MPG...

[Eagle]

I still have (somewhere) a Mopar Stage 2 camshaft kit for a 2.5L. Back when I was still active in NAXJA I corresponded back-channel with a guy from (IIRC) Montana who was running a Stage 3 cam in his 2.5L and said he was averaging 28 MPG.

 

I'm greatly intrigued by the notion of plunking one of the new, Eurpopean CRDs that Chrysler is putting in Jeeps "over there" but won't sell here into an XJ or MJ, but I just can't make myself believe it would ever be worth the time, expense and effort involved. A cam in a freshened 4.0L is just sooooo much easier ...

[gogmorgo]

I've always wanted a smaller diesel engined vehicle, although in terms of availability over here, it's pretty well limited to VW's and Merc's. (My current "dream for next vehicle" which may or may not ever happen would be to swap a VW TDI into a Lada Niva)

 

Terawombat's currently working on swapping a Mazda MZR-CD 2.0L into his MJ. Maybe check that out. http://comancheclub.com/topic/38486-diesel-engine/

[onlyinajeep726]

I posted this a while back.  Might be something to look into also.

 

http://comancheclub.com/topic/39622-rockauto-newsletter-cummins-diesel-mj/

[Oyaji]

Whoops - was posting in the other window I had open, in the wrong thread - trying again here.

.

Interesting comments so far guys - keep 'em coming.

.

I am gonna toss out my choices one at a time and let you pick them apart. Let's start with the OM 617. Pros: acceptable performance in automotive application (revs fast for a diesel), a lot of them around, reasonable price, great reputation for economy and longevity. Cons: not-so-hot-horsepower, it's a non-stock conversion, needs adapter plate, a little heavier than the 4.0 (iirc 600 pounds), old diesel technology (maybe this is a pro, not a con?).

The OM617 engine family was a straight-5 Diesel automobile engine from Mercedes-Benz used in the 1970s and 1980s. It is closely related to the straight-4 OM616. Starting in 1978, a turbocharger was fitted to engines used in the 300SD. With some Mercedes-Benz 300D/300SD diesels already exceeding 500,000 miles, and a few nearing 1,000,000, the OM617 is considered to be one of the most reliable engines ever produced, and is one of the key reasons for Mercedes' popularity in North America in the 1980s, as it was economical, relatively quick (compared to most other diesels on the market) and was trouble-free, unlike the Oldsmobile LF9 diesel V8.

.

The OM617.951 was introduced in 1979 and displaced 2998 cc, using a 90.9 mm bore and 92.4 mm stroke. Power output was 125 hp (91 kW). Torque was rated at 180 lb·ft (244 N·m).

Applications:

1981-1985 300SD Turbo

1981 300TD Turbo

.

Then there is the VM 2.5. Pros: lighter weight, used overseas in stock XJ application, good torque, mechanical injection. Cons: hard to get in the USA, ditto for parts,  just-adequate anemic horsepower.

2.5L TurboDiesel
VM 425 2499 cc (153 CID) I4, OHV Diesel 114 hp (85 kW) @ 3900 rpm 221 lb·ft (300 N·m) @ 2000 rpm VM Motori 425 OHV 1994–2001

[GirsMJ86]

I keep hearing rumors of a small diesel going into the Ram 1500 and Wrangler, supposedly the one that is currently offered in the Grand. The 3.0L EcoDiesel V6 Engine w/ 240 horsepower, 420lb ft torque, and 30 hwy mpg I would guess. No clue if it's any good or not, but maybe someone should go buy a Grand to yank the engine out and test it out?  :thumbsup: 

 

 

EDIT: I guess the rumors are partially true at least, no signs of it in the Wrangler yet. http://www.ramtrucks.com/en/ecodiesel/

[Oyaji]

I like the idea of the VM 2.5 because if it is offered in XJs, then a big pro for me personally is the ease of swap, i.e., motor mounts, harness placement and the whole setup can just be swapped into the MJ.  But, the big con with that as you said is the availability of parts, especially here in the US.

 

Some one posted a thread a while back here on CC about a guy up north that does OM617 conversions on XJs and has done many.  He has all the stuff and his own shop and is certified.  Can't recall the price he would do all this but IIRC, it was quite steep for the average Jeeper's pockets...

.

I thought about getting what they call a "half cut", which is just the front half of an XJ cut off and shipped here from overseas. Evidently it is the easiest way to get what you need. The beauty part is that since it cannot be put on the road, it is classed as "parts" for import. Would probably need to get 2 though, just to have a parts source! I wonder what the total cost would be including shipping...

.

Cost seems to be prohibitive for any diesel alternative, but for someone who intends to keep his vehicle on the road for the long term (like a Comanche owner, for instance :)), I figure that eventually fuel savings would pay for the swap.

.

Eagle's cam swap idea seems to make the best sense so far, practically and financially. But I can't help but think that a diesel would be the perfect swap for a 1986 with a 2.8L V6.

[Oyaji]

I keep hearing rumors of a small diesel going into the Ram 1500 and Wrangler, supposedly the one that is currently offered in the Grand. The 3.0L EcoDiesel V6 Engine w/ 240 horsepower, 420lb ft torque, and 30 hwy mpg I would guess. No clue if it's any good or not, but maybe someone should go buy a Grand to yank the engine out and test it out? :thumbsup:

 

 

EDIT: I guess the rumors are partially true at least, no signs of it in the Wrangler yet. http://www.ramtrucks.com/en/ecodiesel/

.

That is getting to be a pretty strong engine. I bet it has sufficient torque to make frame-twisting a problem. Kinda overkill for a little ole Comanche?

.

I really dislike the idea of a V-6 design with counterweights and balance shafts replacing any inherently-balanced I-6, but I guess if the right V-6 came along it would merit consideration. I never heard of this 3.0 V-6 diesel - I guess it is a bigger version of the 2.8L CRD V-6? Wiring is awfully complicated on the 2.8L CRD, from what I saw... but I guess that would be a mighty sweet package when done. I just don't see myself doing it, nor being able to afford to pay someone else to do it for me (at least not any time soon).

[Eagle]

I really dislike the idea of a V-6 design with counterweights and balance shafts replacing any inherently-balanced I-6, but I guess if the right V-6 came along it would merit consideration.

 

I agree.

 

So how do they balance the 5-cylinder engine you're looking at?

[Oyaji]

 

I really dislike the idea of a V-6 design with counterweights and balance shafts replacing any inherently-balanced I-6, but I guess if the right V-6 came along it would merit consideration.

 

I agree.

 

So how do they balance the 5-cylinder engine you're looking at?

.

That's a good question, and one that occurred to me also. IIRC, the first and second order harmonics are not as bad in an I-5 as in a V-6 (though not ZERO as they are in an I-6),  so maybe they get by with only counterweights.  But ultimately, longevity speaks for itself. The OM 617 I-5 has gone a million miles without overhaul!

.

When I started this thread, it occurred to me that there might be a suitable gasoline-powered OHC V-6 with variable valve timing out there, but it would have to be a really good'un to capture my attention.   But a diesel, on the other hand...

[Crash]

If you can find one, a slightly modded Cummins diesel 4A.. not B is lighter and with similar mods as the 4bt/isb can put out really decent power and awesome fuel economy. 

There are a couple members over @ the naxja forums that have done the Benz 6-cyl diesel swap. 1 or 2 which have done the VW TDI swap as well. 

[dasbulliwagen]

For overhead cam V6 engines, the new Chrysler Pentastar V6 has great power, and if combined with a 3:08  axle setup, and maybe even the 8 speed trans that is offered with it ( it has 2 overdrive gears and is available for 4wd ) would be a killer option if it could be engineered to work with all its electronics. You basically have to have an entire donor and very good wiring diagrams to swap it over and make it all work, but I think it would be worth it.

[carnuck]

I found a Nissan SD33 (wish it was T for turbo) for $2500 with the 727 I considered for a micro second along with the O/D you can bolt between the trans and tcase (by moving everything back 12") They also used 4 cyl diesels in Datsun pickups, most have fallen from the frame of rot.

 

Then I considered a Volvo turbo diesel with the AW4 version automatic bell grafted to a Jeep AW4. Lots in boat yards with rotten hulls but engine mods needed for non-stationary use.

 

Audi diesel RWD engines (5 and 6 cyl) came with a variety of transmissions.

 

Toyota 2LT and bigger were used with AX-15 and AW4 variants.

[Oyaji]

I found a Nissan SD33 (wish it was T for turbo) for $2500 with the 727 I considered for a micro second along with the O/D you can bolt between the trans and tcase (by moving everything back 12") They also used 4 cyl diesels in Datsun pickups, most have fallen from the frame of rot.

 

Then I considered a Volvo turbo diesel with the AW4 version automatic bell grafted to a Jeep AW4. Lots in boat yards with rotten hulls but engine mods needed for non-stationary use.

 

Audi diesel RWD engines (5 and 6 cyl) came with a variety of transmissions.

 

Toyota 2LT and bigger were used with AX-15 and AW4 variants.

.

That info about diesel options  for AW4 and AX15 is tantalizing. I'd like more details,  so I'll start Googling. If you have more  to share, please add  it here if you have the time and inclination - thanks!

[k3y3l3e3]

How about the 2.4l dohc they put in wranglers for a few years came with a 6 speed and a np231 I almost put one Into my mj a wile back wile looking for cool swaps. Plenty of aftermarket support plus they came factory turboed in neons and pt loosers.

[Oyaji]

How about the 2.4l dohc they put in wranglers for a few years came with a 6 speed and a np231 I almost put one Into my mj a wile back wile looking for cool swaps. Plenty of aftermarket support plus they came factory turboed in neons and pt loosers.

.

Interesting.

.

But how much torque does such a little engine put out? Maybe enough to pull a trailer with the 6-speed - but not a heavy one, I reckon... I'd like torque in the ballpark of the 4.0 if possible, and that means a diesel (or re-camming  a 4.0 as Eagle suggested). 

 

Still, if it has variable valve timing, it might do  significantly better than the stock 2.5 on both torque and economy. The 2.5 is already capable  enough if you are not in a hurry, right? So this option is worth a closer look I think. 

[carnuck]

I'd sooner put a Kia Soul direct injected motor in. One in my wife's car gets almost as loaded as my truck (5 adults and luggage) and still gets 30 mpg and flies down the highway!

[terrawombat]

I've always wanted a smaller diesel engined vehicle, although in terms of availability over here, it's pretty well limited to VW's and Merc's. (My current "dream for next vehicle" which may or may not ever happen would be to swap a VW TDI into a Lada Niva)

 

Terawombat's currently working on swapping a Mazda MZR-CD 2.0L into his MJ. Maybe check that out. http://comancheclub.com/topic/38486-diesel-engine/

I WAS going to swap that engine into my MJ, but I do not have the proper tooling to make it happen.  The engine and transmission mounts would have to be complete custom jobs and all of my fabrication goodies are locked up in my shop 3 hours north of me.  Instead, I'll be swapping it into a 1993 Mazda B2200 as the engine block between the gasser that came out of that truck and the block on my diesel are virtually identical.  Also, the transmission from the Mazda truck bolts right up to the diesel engine so I've literally got a drop-in setup, which will just leave me with plumbing of fuel, coolant, P/S and A/C lines (and some wiring) - all completely do-able with my current shop setup.

 

Another quick correction - the engine is actually a Mazda RF-CDT 2.0L.  The MZR-CD is a designation given to this engine when they plopped it in the Mazda passenger vehicles (3, MPV and 6).  The MZR-CD has more power and torque, but also comes with very not-fun features for an engine swap - such as a sentry key immobilizer.

 

While the Mazda diesel engine I have is certainly an option to swap into an MJ/XJ, I don't think I would recommend it based on the effort versus fuel economy you'll get out of it.  If you truly want max fuel economy out of a diesel swap, do a VW 1.9L TDi engine and you can likely get 45+MPG out of it.

[gogmorgo]

I'd sooner put a Kia Soul direct injected motor in. One in my wife's car gets almost as loaded as my truck (5 adults and luggage) and still gets 30 mpg and flies down the highway!

The 3.4 from my dad's 2004 Impala could also get 30 mpg while doing 80mph, loaded down with myself and my sister and all my sister's stuff (to the point where it was almost sitting on the bump stops) on the ten hour trip when I moved her to college a couple times. Just a guess, but I'd say that swap would be a lot less work!

[Oyaji]

Thanks for the ideas guys. I really like the stuff you are coming up with. The ideas I think have the most merit so far are the cam change in the 4.0, the Volvo/AW4 match, and the 2.4 DOHC/6-speed with 231, as they would seem to offer the most bang for the the least work.

.

One thing to point out is that even if another  car demonstrates a certain stellar economy with a given engine, swapping that engine to a truck will NOT yield similar results. Since the shape is different, the aerodynamic load will be different (pick-ups generate horrid drag!), and thus will the  gearing  required for efficient running be different (note that weight has  almost no  influence on economy   at highway speeds, though it does in stop and go urban driving). In the extreme case, a given engine might not even be suitable at all no matter what the gearing is changed to, simply because the torque and power curves may be so incompatible  with the application so as to  be unable to offer acceptable performance over the complete operating envelope.

.

Here is an example. Fella I know was hot to make an entry into the Automotive X-Prize for fuel economy a few years back. To even qualify, all entries had to demonstrate a minimum of 100 MPG. He had custom mounts fabbed (at no small expense) to mate a 17 hp Yanmar 3-banger to a VW-based dune buggy and was sure he was in the running. Early on in the project, via an  introduction by a mutual friend,  he approached me to help him get an estimate (this was  when I accompanied him on the initial trip to the machinist). When after some guesstimation and figuring on scrap paper yielded an estimate of 65 MPG at 40 MPH  and a top speed  of around 55 MPH, he was furious with me,  held faith in his belief (he had no facts to base his belief upon), and I nearly had to walk home! Months later when he had built the thing and the performance fell far short of the requirements to enter the contest, he never spoke to me again... nor would he admit his fuel economy results  to my friend, either. I saw him on the road with the thing a couple times that first year, backing up traffic for a quarter mile... but that buggy has been sitting in his yard for a couple years now. If it still runs, it ain't getting any use at all anymore.

[carnuck]

Agreed on that. The Kia Soul is almost less aerodynamic than the Comanches. I've even been looking for an early one with a blown motor to make a mini pickup out of.