• DCRC 2024

4bt motor swap in a 2008 Jeep JKUR

Greg

Greg

Make RME Rockcrawling Again!
Admin
Location
Grand Junction, CO
MikeGyver said:
All the swaps listed on that link are like 19mpg avg. Where is this biazrre universal idea coming from that you'll get 30-40mpg avg?
The only reason its even getting 19 is because it's a very low power motor, same reason my saturn gets 37mpg avg and I'm flooring it quite alot (just to get up to speed).

Tq by itself means absolutely noting. If an engine has half the rpm range, it better have double the tq. I think a stock LS motor actually has more tq off idle at and most definitely across the board than a stock 4bt anyway, and revs to 6krpm so it makes double the power for essentially the same mileage. Double the tq but half the rpm range is exactly the same net effect as doubling your final gearing, it doesn't add performance, power, or mileage (...well maybe crawling performance, since your motor is stuck in low range).
If you accelerated as slowly in the same rig with LS power and appropriate gearing you'd probably get the same mileage. Diesel contains a bit more energy than gasoline, but a new generation gas motor is more efficient in design than an old motor from a breadtruck.

and an LS might actually even be easier to wire up, since there are many swap harnesses that only use a couple wires.
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IMO, lots of people fib and round up their numbers... then they get around their buddies or on the internet and the numbers magically grow. ;)

I'm not claiming any more than what that MPG average thread on 4BTSwaps says. Mid-20's is about the best they'll do on average. That thread has lows of 18 MPG and highs up to 29 MPG. It all depends on how you drive it, how you gear it, what transmission (manual vs. auto) and how the vehicle is built, obviously. IMO most 4BT's are in big, heavy 4x4's so that has an effect on the numbers as well. The one guy that claimed 32 MPG is running a Isuzu 4BD1T, which is a totally different animal compared to a Cummins 4BT.

So you're telling me that a 6.0l LQ4 is going to get 15-20 MPG? Riiiighht... I'm around 1 ton trucks GM trucks with 6.0's all day long at work and 8-9 MPG is the best they'll do. So if a LQ4 is getting 9 MPG and the average 4BT is getting 25 MPG, then it's getting 2.7 times the mileage! Hard to argue real world numbers, isn't it?

Torque means everything when it comes to moving a vehicle... your talk of splitting power and doubling RPM is interesting, never thought about it that way. Fuzzy math to say the least.. ;) Yes, you have to gear a 4BT differently than a gas motor, why is that a surprise to you?

More than a few people have mentioned how these are 'old' tech... apparently nobody realizes there is a new version of the 4BT? There's a Cummins 4.5l QSB that is computer controlled, makes more torque than a 'old' 4BT and gets better mileage as well... it also burns MUCH cleaner exhaust. This QSB 4.5l is basically a 4 cyl version of the newer Cummins 6.7l in the Dodge trucks, it has a common rail injection system, the geartrain is in the back, rather than the front, etc. They're not nearly as friendly to turn up, as they are 100% computer controlled and Cummins is holding tight onto the software. On top of that they're not rated for on-road use. A Cummins tech has claimed that with a better turbo and a different tune, a QSB 4.5l can make 300 Horsepower and well over 600 ft/lbs. Due to the ease of finding cheap 4BT's and how new the QSB engines are, plus the lack of software knowledge, it's obvious to see why they're not being used near as much.

Obviously you don't like diesels... that's fine. Some people do, some people don't. I like LSx engines and I like diesel engines... :greg: I've swapped a 5.3l into my old TJ but my next engine swap will be a diesel. :p
 
MikeGyver

MikeGyver

UtahWeld.com
Location
Arem
Greg said:
So you're telling me that a 6.0l LQ4 is going to get 15-20 MPG? Riiiighht... I'm around 1 ton trucks GM trucks with 6.0's all day long at work and 8-9 MPG is the best they'll do. So if a LQ4 is getting 9 MPG and the average 4BT is getting 25 MPG, then it's getting 2.7 times the mileage! Hard to argue real world numbers, isn't it?
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If you swapped a 4bt into that exact same vehicle it wouldn't average 25mpg if it was driven around town at the same acceleration speeds as before. Most of the mileage improvements would be due to the smaller 140hp(?) motor so it probably couldn't maintain the same pace as before. If you limited the LQ4 version of the truck to a comparable 140hp it would of course jump in mileage too. The vehicle gearing would of course need to be optimized for either engine, this isn't surprising... (?)


The reason I say tq is meaningless on it's own is because tq and rpm are just essentially inversely proportional sides of the equation that is power. Power is the ability to do work, not tq, not rpm. Power is the end result. power is power regardless of how it's made. Power is what moves a 6000lb truck from point a to point b in x time. If you had 2 different power sources each making an absolutely constant 50hp but at greatly different rpm's and tq levels, it wouldn't make the slightest bit of difference as far as performance. Roughly speaking, avg power on a trip times total system efficiency is equal to mileage.

The moral of the story: The mileage gains from a 4bt swap are because you're trading off performance/power potential.
The same reason the little 4 cylinder version of a car gets better mileage that the V6.


*And it's not fuzzy math...
1tq @ 2 rpm actually equals 2tq @ 1rpm
It's just simple gear reduction.
 
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Greg

Greg

Make RME Rockcrawling Again!
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Grand Junction, CO
MikeGyver said:
If you swapped a 4bt into that exact same vehicle it wouldn't average 25mpg if it was driven around town at the same acceleration speeds as before. Most of the mileage improvements would be due to the smaller 140hp(?) motor so it probably couldn't maintain the same pace as before. If you limited the LQ4 version of the truck to a comparable 140hp it would of course jump in mileage too. The vehicle gearing would of course need to be optimized for either engine, this isn't surprising... (?)


The reason I say tq is meaningless on it's own is because tq and rpm are just essentially inversely proportional sides of the equation that is power. Power is the ability to do work, not tq, not rpm. Power is the end result. power is power regardless of how it's made. Power is what moves a 6000lb truck from point a to point b in x time. If you had 2 different power sources each making an absolutely constant 50hp but at greatly different rpm's and tq levels, it wouldn't make the slightest bit of difference as far as performance. Roughly speaking, avg power on a trip times total system efficiency is equal to mileage.

The moral of the story: The mileage gains from a 4bt swap are because you're trading off performance/power potential.
The same reason the little 4 cylinder version of a car gets better mileage that the V6.
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I feel like you're arguing my point about the gearing... so, yeah. Glad we're on the same track. :p

You asked why these are popular, I tried to answer your question. There is still plenty of power to be squeezed out of a 4BT, there are guys running twin turbos and 60+ PSI of boost making close to 600 ft/lbs with 4BT's that have plenty of 'performance'. Sure, using that power won't net you 25 MPG... but that makes your argument about performance/power potential null and void. I don't know what kind of mileage those trucks are getting, but I'd be curious what they do when driven 'normally'. That said, I think that's a lot of the draw to these engines... the ability to tweak how the power is made and squeezing all kinds of power out of something different than the norm.

That said, I'm not even a big fan of the 4BT... :cody: I'm done here. :)
 
Tacoma

Tacoma

Et incurventur ante non
Location
far enough away
4bts dont' give anyone huge mileage in the real world. They work, they fit, but they're heavy. LS motors dont' give anyone huge mileage either, but gas is cheaper, and the buy-in is generally cheaper, as are conversion parts. I've done the math before and over the lifetime of most of our ownership cycles on the average RME truck, the gas motor makes a lot more sense-- but none of this is about sense, necessarily-- it's about what we want to tinker with. So have at it, blow up your front axle, and realize a few things along the way, have a bitchin' build thread in the meantime. heh
 
Greg

Greg

Make RME Rockcrawling Again!
Admin
Location
Grand Junction, CO
Tacoma said:
...but none of this is about sense, necessarily-- it's about what we want to tinker with.
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Amen brotha! Swapping a gas motor in place of another gas motor isn't what gets me excited... I want to play with a diesel, turbos & boost! It's my money and I'm going to do what I want with it. :D
 
Unimog

Unimog

Eric
Location
Stansbury Park, UT
Tacoma said:
...but none of this is about sense, necessarily-- it's about what we want to tinker with.
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This is really the key. I would say that a lot of the guys I know who do an engine/drivetrain swap, me included, could get a more "economical" result by buying a rig that is already equipped with a similar/better than current drivetrain. Most of us like to tinker and like having something a little (or a lot) different than the next rig. If this weren't the case, we'd all be driving stock rigs if the same make [insert your favorite brand here]. I would love to see this 4bt build thread. It doesn't have to make sense to be enjoyed!
 
jeep-N-montero

jeep-N-montero

Formerly black_ZJ
Location
Bountiful
If I had the money to blow and didn't need to worry about inspections I would likely look at doing a cool diesel engine swap. When we were in Moab in May there was a guy camped by us with a sweet first gen Cummins Ram for a tow rig and his trail rig was a YJ with a 4bt swap, the entire setup just had such a coolness to it all if you will.
 
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R

rholbrook

Well-Known Member
Location
Kaysville, Ut
I went and looked at the new Grand Cherokees with the diesel in it today. May be worth keeping an eye out for a wrecked one and pull the engine and 8 Speed tranny out one of those. That would be a cool swap. They have a 7,500 tow rating which means the engine will have plenty of get up and go.
 
spencevans

spencevans

Overlander
Location
Farmington
I have a 2009 VW Jetta Sportwagen with the 6 speed manual and I average about 33-40 mpg. I have seen upwards of 46mpg on the open road at 62mph. I can't imagine a big heavy JK with a 4BT coming close to that. I do have a 1985 Mitsubishi Pickup with 12" of lift and JK rubicon axles, that gets 40mpg on the open road, but it has a tiny 2.3 liter Mitsubishi diesel that sips fuel and the truck only weighs 3000lbs. I still think your best bet is a 3.0 Mercedes Diesel out of a 2007 Jeep Grand Cherokee. I bet it would make for one clean and cool swap. It sounds so cool I am thinking of doing it.
 
spencevans

spencevans

Overlander
Location
Farmington
rholbrook said:
I went and looked at the new Grand Cherokees with the diesel in it today. May be worth keeping an eye out for a wrecked one and pull the engine and 8 Speed tranny out one of those. That would be a cool swap. They have a 7,500 tow rating which means the engine will have plenty of get up and go.
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They appear to be a great diesel and I can't wait for them to find there way into the new Ram 1500 Pickup. The 3.0 liter V6 diesel in the 2014 Grand Cherokee is manufactured by VM Motori, the same company that produced the 4 cylinder, 2.8 liter diesel for the 2005-06 Jeep Liberty. The diesel previously found in the Grand Cherokee was a 3.0 liter produced by Mercedes.

I owned a Liberty diesel and put 50K miles on it before the wife totaled it and I was never happy with that engine. It was always in the shop for something. It had EGR issues and it turned me off of VM Motori engines. I hope this new one is better.
 
N8RB8R

N8RB8R

Well-Known Member
Location
Elk Ridge
Greg said:
Amen brotha! Swapping a gas motor in place of another gas motor isn't what gets me excited... I want to play with a diesel, turbos & boost! It's my money and I'm going to do what I want with it. :D
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I agree! Duramax JK coming up!
 

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bryson

bryson

RME Resident Ninja
Supporting Member
Location
West Jordan
rkillpack said:
Not to take away from what Nate is taunting this thread with, but I'm sure that Jeep will be around for quite a while. After all for the owner, the Duramax is phase 4 of 5 for a Jeep that hopefully someday soon will finish the Baja 1000. So my sources tell me.
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You are such a tease...
 
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