Is 11.7 h-mpg terrible? Ideas for future engine swap. - JeepForum.com
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post #1 of 19 Old 08-18-2017, 11:22 AM Thread Starter
redblur
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Is 11.7 h-mpg terrible? Ideas for future engine swap.

So I just returned from my 89 YJ's maiden voyage after years of work, and it was simply bliss to finally drive her on the highway for hours on end with the top down. I had a huge grin from ear to ear.

However, I realized that the jeep is still as slow as the speed of smell. It's an 89 YJ with a 4.0L from a '92, AX-15, ECGS rear Dana 44 swap, 4.5" of lift on 33's with 4.10 gears. It accelerates decently, but on the highway holding 70 mph was difficult. My particular voyage took me through the hills of Pennsylvania on highway 80W and various backroads. On normal flat stretches, 5th gear and 1/3 throttle was sufficient. I often found myself on long inclines in fourth gear with my foot to the floor just to hold 70 mph on the highway. Is this typical of 4.0L's with lifts and bigger tires?

Also, since my foot was to the floor half the time trying to keep up with the rest of the group and traffic, fuel economy tanked. In the city, on the way to work normally, I get 11.2 mpg. On the 140 miles spent on the highway, I got 11.7 mpg primarily because I was just trying to keep up. And since the trip is about 270 miles total, I can't make it door to door on a single tank. No Buenos.

The point of the story is this:

1st part: Is there an engine swap out there that would increase power available for hills and Miles-per-gallon at the same time? I've researched the various LS V-8's and 4.0L strokers, but I don't want to stray too far from factory parts and availability. I work supply-support for the military, and logistical support is a major concern for me. If a custom swap-specific radiator or clutch from Advance-Adapters breaks, I can't find another at Autozone or Napa in the middle of nowhere. I need to be able to find parts regularly from a variety of sources, or pull them off a junkyard jeep.

2nd part: I count my wrangler as my primary "SHTF" vehicle, so the future engine swap has to run off a commonly-available fuel i.e. 87 octane (that's a year old) or diesel. I was considering the Golen 4.6 stroker because of its interchangeability with the current setup, but it runs off 91 octane and probably gets less MPG than the current 4.0L. If I run a diesel swap (which would undoubtedly help in MPG and TQ), can I find parts for the motor and accessory systems on existing vehicles?

3rd part: Or do I just add an intake and exhaust and see how that helps? This would probably be easiest.

Apologies for the rambling, but I figured I would get the advice of the forum before I plan to spend $5-8K on an engine swap. The swap won't happen until the 4.0L dies, but I like to plan things out. Thanks much!


1989 YJ with '92 4.0L, '91 AX-15, NP231 w/ JB SYE, 5" lift, 33's, Warn M8000, ECGS Dana 44 rear.
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post #2 of 19 Old 08-18-2017, 11:52 AM
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Has your speedometer been regeared? If not, it is going to be pretty far off with 33".

I get about 11.5 city and highway (doesn't change it much). I have not corrected my speedo either, and it is off about 10%. So that puts me somewhere in the 12's. That's with a 4.2 and fuel injection. I would expect a little more out of a 4.0, but not a huge amount. In fact, correcting the speedo would make it look pretty good.

I can't really add anything on motor swaps. Personally if I did anything, I would regear it and stop for gas.

Bill
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1988 Wrangler,4.2L I-6, Howell EFI JP-1,CRT HEI Ign,AX15 ext slave conversion, Zone 2.5" lift + 1/2" booms, BFG 31 x 10.5, Bestop.
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post #3 of 19 Old 08-18-2017, 11:56 AM Thread Starter
redblur
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Thanks for the response. Yes, I replaced the speed gear with the correct on for 4.10's and 33's. I checked the speed with a Garmin GPS, and the speedometer is only 1 mph off. I'll wait and see what other people are getting for MPG's to compare.

1989 YJ with '92 4.0L, '91 AX-15, NP231 w/ JB SYE, 5" lift, 33's, Warn M8000, ECGS Dana 44 rear.
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post #4 of 19 Old 08-18-2017, 12:49 PM
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Carb'd with a 2100 and HEI on 35's and 4.88's. 11MPG is about what I get no matter what.
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post #5 of 19 Old 08-18-2017, 02:34 PM
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I never checked fuel mileage. Don't care.
But something is definitely wrong if you can barely do 70.
If I run it hard, I'm doing 90 and have topped mine out at about 100.
That's on a dry lake bed so it's flat & level by nature.

My Jeep is NOT a Fiat!
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post #6 of 19 Old 08-18-2017, 02:42 PM Thread Starter
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Oh it'll do more than 70 flat and level. It just takes a while. My concern was upping the fuel economy and not have to full throttle it on a steep grade. I was considering diesels but dang, they're expensive. But then again, so would a LS 4.8L V8.

1989 YJ with '92 4.0L, '91 AX-15, NP231 w/ JB SYE, 5" lift, 33's, Warn M8000, ECGS Dana 44 rear.
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post #7 of 19 Old 08-18-2017, 03:09 PM
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Diesels are my life.
I'm a heavy equipment operator and have a diesel one ton pickup.
I don't think a diesel is a good Jeep option because of the limited RPM range.

The fuel mileage will not change much with an engine swap.
It's simple physics.
The YJ is a brick and will always be a brick.
It takes a certain amount of energy to displace X amount of air at Y speed. That air increases with height and add the effect of turning heavy flywheels (big heavy tires)
Horsepower is horsepower.

My Jeep will keep up 70 on a 6% to 7% grade. But the throttle is also 3/4's. But so is everyone else's.

How is your gearing?
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post #8 of 19 Old 08-18-2017, 03:36 PM
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I cruise easily at 70/75, more if my balls are blue enough. But I definitely feel any hills too, and hills mean downshifting out of 5th. I can really only use 5th on very flat highways.

I'm interested in whatever is suggested for engine swaps. My expectation is that there isn't going to be much economy to gain. And I definitely don't think it is worth it just to avoid buying some gas. Simple fun is the only reason to swap engines.

I pay attention to mileage very closely. I log ever drop of gas purchased, and every mile driven. OCD? Yeah probably. It's not like I am worried about it. But if there is a big drop off in mileage, it can be a symptom to notice. Avoids burning out cats if nothing else.

Oh, one other thing, I don't trust ANYONE who tells me their gas mileage on a forum. So if some post looks too good to be true...

Bill
Dodge did not build my Jeep.
1988 Wrangler,4.2L I-6, Howell EFI JP-1,CRT HEI Ign,AX15 ext slave conversion, Zone 2.5" lift + 1/2" booms, BFG 31 x 10.5, Bestop.
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post #9 of 19 Old 08-19-2017, 01:56 PM
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Its not the fun answer but slowing down to 60-65'ish will help out the most. As for an engine swap you cant go wrong with a 5.3L from GM.
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Jim...

"That's more fun than watching a hippie get mauled by a bear!"
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post #10 of 19 Old 08-19-2017, 02:15 PM Thread Starter
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ShaggyJim, wouldn't a 5.3L require a bunch of specific parts though? Like clutch/flywheel/radiator/wiring/alternator/etc? That's a big concern if I couldn't find those parts at a corner store. But I would imagine with a lighter motor and a bit more efficient, mpg's would go up slightly. Anybody that has a diesel can weigh in?

1989 YJ with '92 4.0L, '91 AX-15, NP231 w/ JB SYE, 5" lift, 33's, Warn M8000, ECGS Dana 44 rear.
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post #11 of 19 Old 08-19-2017, 03:22 PM
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You just talked about light weight?
Then mention a diesel.
Those two should not be used in the same paragraph.

Remember, a diesel has 2000 usable rpm.
The 4BT vibrates like a paint shaker and in stock form, lacks horsepower.

It would be easier and cheaper to pick up a used Subaru or Toyota for commuting.
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post #12 of 19 Old 08-19-2017, 06:25 PM
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Quote:
Originally Posted by redblur View Post
ShaggyJim, wouldn't a 5.3L require a bunch of specific parts though? Like clutch/flywheel/radiator/wiring/alternator/etc? That's a big concern if I couldn't find those parts at a corner store. But I would imagine with a lighter motor and a bit more efficient, mpg's would go up slightly. Anybody that has a diesel can weigh in?
I think it will require a bunch of specific money more so then a bunch of parts. You would need a new radiator, motor to frame mounts, trany adaptor, and is some cases a new fuel pump. Everything else should be stock GM or Jeep. From what I have been able to research "I haven't done this swap" from the Novak site the install can be worked out down to a three wire hookup for a running engine. Is there more to it then that..... I'm sure! Isn't there always. However the swap has been done countless times with great success. As to the other question of a diesel option I have looked into that quite a bit and don't think a IMO good choice is out there sense Banks discontinued the 630T. I did run across something to day that said Advanced Adaptors is working Cummins to put out a direct to consumers all inclusive 2.8L I4 engine/adaptor package that is 50 state emissions compliant! I will see if I can find the link.

Jim...

"That's more fun than watching a hippie get mauled by a bear!"
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post #13 of 19 Old 08-19-2017, 06:30 PM
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Here is the link. Watch the video!


http://www.4wdmechanix.com/advance-a...sion-for-jeep/

Jim...

"That's more fun than watching a hippie get mauled by a bear!"
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post #14 of 19 Old 08-19-2017, 06:42 PM
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Quote:
Originally Posted by shaggyjim View Post
Is that diesel the one that was in the Liberty?

If so, that one wouldn't be too bad.

However, spending that kind of cash to replace a legendary I-6?
Blasphemy.

And if fuel economy was the goal, how long would it take to make up for the $$ spent?

I may supercharge my Jeep this spring.
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post #15 of 19 Old 08-19-2017, 06:51 PM
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Nope Its newer engine from Commins. I think the one in the liberty was Italian but Im not sure. How long to recover the cost..... hmmmmm... 128,563.8 miles. Its still SWEET!
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