Best diesel mpg with equal power?

[memphisjim]

Ok I've been planning what to do when I get around to upgrading my engine. I've now been reading about the diesels and double the gas mileage!!!
It seems the 4bt and the isuzu seem pretty popular. I can't find info but the power stroke 4.5l looks like q good motor too.
Which of these motors will give the beat gas mileage , with the caveat that it's power must be increased to at least match a stock 360? And by match I'm talking seat of the pants and 0-60 time. What hp does the 4bt need to be increased to to match a 360 0-60?

[memphisjim]

Are these hard questions?

[lobie]

It's hard to answer your question. I am only familiar with the cummins. You can't talk HP with diesels. They are set up for torque. The 4bt is comparable to the 360 in torque with better fuel mileage. They can easily be modified to out produce the 360.

[memphisjim]

As I understand it diesels rev more slowly. So how much of a torque advantage does it need to have to compare with a gas engine in acceleration

[CutterN55]

you could get a quicker & higher spoolin turbo, but they aint cheap. I'm just learning about diesels though...and I have only messed with the bigger ones.

[lunchbox1671]

As I understand it diesels rev more slowly. So how much of a torque advantage does it need to have to compare with a gas engine in acceleration

Diesels don't necessarily rev slower than a gas engine. Most have a lower peak RPM than gas engines. The difference you are referring to is the peak power/torque curve. Diesel engines will produce their peak power at a lower RPM than a gasoline engine.

If you want comparable acceleration to your stock 360 without getting into expensive aftermarket turbos, then you need to look at your transmission, axle gearing, and tire size.

[PlasticBoob]

The inability of the garden-variety diesels to match the HP and torque of my current 401 also has me on the fence regarding a future diesel swap. Though I think I'm at the point where I want to keep my rig mostly original and stick with a 401, I will be following this thread closely.

[memphisjim]

i was thinking power and really considering finding a 401 but then i read about the mileage improvement double basically and a little speculation of biodiesel fuel in the future has me thinking diesel

also i dont mind putting some money into the engine so long as the power increase is worth it, the mpg doesnt suffer much, as well and little loss in the longevity of the motor

[jwalton23]

i was thinking power and really considering finding a 401 but then i read about the mileage improvement double basically and a little speculation of biodiesel fuel in the future has me thinking diesel

also i dont mind putting some money into the engine so long as the power increase is worth it, the mpg doesnt suffer much, as well and little loss in the longevity of the motor

It doesn't matter what kind of motor you upgrade the gas mileage, longevity, and fun per gallon will be affected. A Diesel engine with 1000 hp and a gas engine with the same are going to preform totally different. its all in how you build it and what your plans for driving it are.

[memphisjim]

It will be a daily driver It will have 33's at best. I'd like to stick with an automatic tranny. It's seems 200 hp out of a 4bt if pretty doable And that puts the torque over 400 The power difference is signifigant would it out run a 360? Also how much mpg would I lose by increasing the power to that level?

[lobie]

You may want to surf around on 4btswaps.com
Theres a lot of info that may answer your questions.

[Mikel]

The inability of the garden-variety diesels to match the HP and torque of my current 401 also has me on the fence regarding a future diesel swap. Though I think I'm at the point where I want to keep my rig mostly original and stick with a 401, I will be following this thread closely.
I have a 6BT with $100 worth of power upgrades in my 8000lb M715 and I can lay rubber in second and third gears (I have five).

My other truck, the J300 has a tweaked 4BT with performance comparable to most 360's I've driven... And I get 23-25MPG.

[Mikel]

It will be a daily driver It will have 33's at best. I'd like to stick with an automatic tranny. It's seems 200 hp out of a 4bt if pretty doable And that puts the torque over 400 The power difference is signifigant would it out run a 360? Also how much mpg would I lose by increasing the power to that level?
Most 360's are rated from 140 to 170 HP. You can easily surpass that with a VE 4BT by turning a few screws and replacing the governor spring ($30). 250HP seems to be where the easy/cheap limit on 4BT power ends. My 4BT feels like a more powerful engine and is only affected by the wide spacing of the gears in the NV4500.

After tweaking my injection pump, I lost 1MPG, but probably has more to do with my driving style :drivin:

[PlasticBoob]

I have a 6BT with $100 worth of power upgrades in my 8000lb M715 and I can lay rubber in second and third gears (I have five).

My other truck, the J300 has a tweaked 4BT with performance comparable to most 360's I've driven... And I get 23-25MPG.
For sure! No doubt the 6BT is the way to go, but I don't consider it "garden-variety" because from what I've read, it's a lot of work to squeeze into a Cherokee. One guy had to modify his razor grill for the intercooler, others have to hack up the firewall, and I've read that upgrading the front suspension and axles is a must for durability. That's wayyy beyond my pathetic capabilities, haha.:o Anyway, by "garden-variety" I meant the 4BT, GM 6.2/6.5, and all the other small 4cyl oddball diesels people suggest.

It's funny how you say the 4BT practically maxes out around 250hp, because that's what I also found in my research. Compared to my 401 (currently around 280hp, 400+ft-lbs), I'm a little spoiled and don't think I'd be comfortable "stepping down". :confused: Oh well, this is all way down the road when 401 parts can't be found reasonably cheap anymore.

[Mikel]

For sure! No doubt the 6BT is the way to go, but I don't consider it "garden-variety" because from what I've read, it's a lot of work to squeeze into a Cherokee. One guy had to modify his razor grill for the intercooler, others have to hack up the firewall, and I've read that upgrading the front suspension and axles is a must for durability. That's wayyy beyond my pathetic capabilities, haha.:o Anyway, by "garden-variety" I meant the 4BT, GM 6.2/6.5, and all the other small 4cyl oddball diesels people suggest.


Regarding the 6BT, you can fit a non-intercooled one very easily and still smoke any stock V8 Jeep put into a FSJ without getting EGTs into an alarming range. The front axle will probably handle the extra weight unless you are hard on the truck. I went with a D60 front partially because of the much larger brakes.

It's funny how you say the 4BT practically maxes out around 250hp, because that's what I also found in my research. Compared to my 401 (currently around 280hp, 400+ft-lbs), I'm a little spoiled and don't think I'd be comfortable "stepping down". :confused: Oh well, this is all way down the road when 401 parts can't be found reasonably cheap anymore.


Well, I said "easy/cheap power". There are people in the 4BTswaps site who are just under 400HP with a 4BT, but I'msure it wasn't cheap or easy. A 250HP 4BT will probably feel more powerful than a 280HP 401 due to its immediate torque delivery. It is all about usable power...

[dusty]

For sure! No doubt the 6BT is the way to go, but I don't consider it "garden-variety" because from what I've read, it's a lot of work to squeeze into a Cherokee. One guy had to modify his razor grill for the intercooler, others have to hack up the firewall, and I've read that upgrading the front suspension and axles is a must for durability. That's wayyy beyond my pathetic capabilities, haha.:o Anyway, by "garden-variety" I meant the 4BT, GM 6.2/6.5, and all the other small 4cyl oddball diesels people suggest.

It's funny how you say the 4BT practically maxes out around 250hp, because that's what I also found in my research. Compared to my 401 (currently around 280hp, 400+ft-lbs), I'm a little spoiled and don't think I'd be comfortable "stepping down". :confused: Oh well, this is all way down the road when 401 parts can't be found reasonably cheap anymore.


My 401 was a 9.8:1 with a .525 lift cam and a 770 holley, headers dual exhaust hei, a snorty little motor that tuned in at the 440 ft/lbs mark. my 4bt with 200 hp turned 498 ft/lbs at the rear wheels and flat out pulled my 401 especially with a load. my 401 had to be into the 4bbl to do what that 4bt could do. its a trade off but when that turbo lit that chief flat got with it in my opinion........ whats your 401 put down at the rear wheels because i can tell you it isnt 400 ft/lbs. even empty my 4bt was no sloutch, though i lost the rumpity rump and the off the line snap the driveability and double the mileage with equal power at cruise and better towing power without detonation issues and heat issues sure made me a believer and im a die hard 401 fan

[memphisjim]

ok i got a decent reference today
i rode in a 1998 z71 with a diesel im assuming its a 6.5l turbo
that truck would definitely outrun a stock wagoneer
can a 4bt in a wag match this without losing too much mpg or durability?

[The Colonel]

ok i got a decent reference today
i rode in a 1998 z71 with a diesel im assuming its a 6.5l turbo
that truck would definitely outrun a stock wagoneer
can a 4bt in a wag match this without losing too much mpg or durability?

Try getting hold of this member: http://www.ifsja.org/forums/vb/member.php?u=5105
He recently did a 4BT swap.

[tndonor]

There are many variables to get in order before we compare apples and oranges.

OD transmission?
BSFC of motor (where it makes the best fuel econom)
manual vs auto (if auto TC stall)
axle gearing
lift
tire size
vehicle weight
motor stock or not
turbo size, exhaust housing size, etc

Im not saying answer all these. There are just so many variables, many I didnt put here that could sway the numbers however one would like.

Its all what you want to accomplish. You can have a quick diesel. With power and fun comes diminished fuel economy. Any time you increase performance, longevity generally goes down. Because Diesel typically go longer before major overhaul, this seems to be delayed because even still they out last many gas motors tweaked in a similar manner.

Doesnt really answer your question. I dont think you can answer your question with 100 percent certainty. In the end it is what you can spend, live with, and like.

[memphisjim]

the z71 was stock with auto transmission dont know about gear ratios but it didnt seem to shift at a low speed or anything

[joe]

As with the Z71, driving actual vehicles is you best bet. Keep good notes too. As tndonor mentioned "lotsa" variables. Axle gear being a major one. I've got two dsls Ford F250/IH 6.9 NA/ T19 and a C20/6.2NA/Th400. The Chev is somewhat quicker and tows better. I contribute the difference to the axle gears 3.54's in the Ford, 4.10's in the Chev. Both running 33's
If you drop even a 300HP dsl in a stock 2.73/3.31 geared FSJ it's gonna be a slug at streetlight tag.

[kyamcalvert]

so long as the power increase is worth it, the mpg doesnt suffer much, as well and little loss in the longevity of the motor



IMHO, this is setting yourself up for disappointment. I am by no means a guru and I have never built a motor, but I have spent what's probably thousands of hours online researching diesels and diesel swaps. Recalling all the millions of threads and articles I've read, it seems pointless to me to "slightly" build a motor. The way I see it, you get power or you get mileage. Diesel motors in general are a great combination of both (for pulling things, not peeling out), but when you build any motor for power, mileage loses out every time. It's sort of like the teenaged tuner rice burner kid (who seem to be EVERYWHERE by the way) who thinks a turbocharger will give him 30 miles per gallon and 500 horsepower. Just my two cents.

[mdill]

The cool part of the Diesel's and turbos, is you can build a engine to get gob's of power and still get good MPG.
The trick to doing that is in the turbo setup, and working a compound setup that will spool quick from idle but build boost at full flow. (It also has to have a low restriction waste/intake path for running close to NA when boost is not needed (mpg mode)
With a Diesel you don't have to knock the CR down as much as with a gas motor to run big boost numbers, (nothing in the hole to predetonation)
But you have to build a lower end to take it, have a pretty fancy turbo setup ...
It is about as close to a variable displacement engine setup as you can practically get.

[Mikel]

IMHO, this is setting yourself up for disappointment. I am by no means a guru and I have never built a motor, but I have spent what's probably thousands of hours online researching diesels and diesel swaps. Recalling all the millions of threads and articles I've read, it seems pointless to me to "slightly" build a motor. The way I see it, you get power or you get mileage. Diesel motors in general are a great combination of both (for pulling things, not peeling out), but when you build any motor for power, mileage loses out every time. It's sort of like the teenaged tuner rice burner kid (who seem to be EVERYWHERE by the way) who thinks a turbocharger will give him 30 miles per gallon and 500 horsepower. Just my two cents.

I have a 4BT in my J300. I went from the stock 105 HP settings to almost twice of that, with no significant loss in MPG. It all comes down to how you drive. I only use the extra power 5% of the time, so overall fuel consumption remains fairly untouched.

My best tank was 25.2MPG and my worst about 22. Better than the 11MPG I got with the V8...


My 8000lb 6x6 M715 with enough power to smoke the tires in the first three gears and the aerodynamics of a barn door gets better MPG than most stock FSJs.

[memphisjim]

Mikel u sound like u drive like me. I drive bikes fast and 4 wheelers slow, most of the time. It's down the road before I'd ever do a transplant. I thought I needed a rebuild my brother looked at the 360 and asked if I knew that a spark plug wire was cut. Well I didn't and can a 4bt be as smoothe as a 1991 360?
Sorry all that's true but I just graduated from the university and I'm now drunk Im not pretentious and I love the grand wag but 10 mpg won't cut it But now and again I like to punch the pedal and feel something. Well I graduated and got one of these IPhones so next message may or not be better. Ps I have 2 1991's an 1998 and some junky earlier one think 1987

[memphisjim]

Also on these screws you turn on a 4bt to gain horses and torque
Can you just turn them back down when u want ?

[budojeepr]

Also on these screws you turn on a 4bt to gain horses and torque
Can you just turn them back down when u want ?
I have the GM 6.5 in mine...there's one screw in the injection pump that you can turn to get more fuel in...but mileage will suffer. You can also install different injectors to get more power ...but mileage will suffer.

I have 2.73:1 rear axle ratio and rational tires and can still launch with liberal (one-sided, no locker yet) wheelspin. She takes the highway onramps like a dragster but can cruise comfortably at 75 all day, at 22 to 24mpg.

The whole package is a good compromise of uses. No regrets at all.

[tndonor]

Even comparing the different Diesel options is apples and oranges. I wont get into which is better debate. I will say the the J10 I had was a 6.2 Diesel before it was a Cummins 4bt. As far as I know, I am the only one to have had both platforms in the same truck.

The GM 6.2/6.5 makes power more similar to a gas motor. The 6.2 you have to spin up north of 3000 rpms to make the peak power. The torque increases with the rpms. The Cummins makes peak torque by 1600-1900 depending on the CPL and remains flat across the rest of the powerband.

You can add fuel to the GM units by adjusting the standyne pump (injection pump). However, the gains are small due to the highest compression ratio of the Diesel (21:5). Thats why anything above 10 psi of boost will destroy the motor. Injectors are expensive and produce small gain will loss in MPGs. The main reason the gains are small is the amount of tuning you can do is very limited.

The cummins platform is just about the opposite.

The 7.3s are about in the middle of the two.

Now a lot of this changes once you get into the Durmax, powerstoke, and ISB Cummins.....the plug and play helped out as timing, fuel delivery,etc could be tuned by turning the knob in the dash to 10. You also have to make these motors run with ECMs, PCMs, etc.

There are tons of opinions on this subject here and a myriad of other boards. I would say only take into consideration those who have DONE it and have some data. IF you are curious to my biased......just look at my sig:D

[TPICherokee]

ok i got a decent reference today
i rode in a 1998 z71 with a diesel im assuming its a 6.5l turbo
that truck would definitely outrun a stock wagoneer
can a 4bt in a wag match this without losing too much mpg or durability?

My 1996 Suburban with a 6BT Cummins (not built, just has the pump turned up a little) blew the doors off of a 6.5T GM truck of the same era. He got me once we hit about 75 but that was because he had a higher redline than I, that was about as fast as I can go.

This was apples to apples -- aside from I was heavier since he was a pickup -- both trucks had 4.10 gears, tires were within 1/2" of eachother, both trucks had a 4L80E and both were 4WD.

Now you are talking about a 4bt which should make plenty of power but not quite like a 6bt. They can be made to make a bunch of power.

From what I understand (and have been experiencing) on a Cummins, the more power you can make (without smoke) the more mileage you will have assuming you can keep your foot out of it.

My best tank in the Suburban is 18 MPG, towing 10k I get around 13. This is a little lower than I expected but I attribute this to the 4.10 gears which are a little steep (about 2100-2200 rpm at 65 and I tend to not keep it at 65).

[dusty]

..........Well I didn't and can a 4bt be as smoothe as a 1991 360?


No a I4 will always vibrate more than a 6 cyl or V8.

[Mikel]

No a I4 will always vibrate more than a 6 cyl or V8.

Not going to argue that, but my 4BT (with the idle raised a bit) is surprisingly smooth.

[The PIG Smith]

No a I4 will always vibrate more than a 6 cyl or V8.
Not going to argue that, but my 4BT (with the idle raised a bit) is surprisingly smooth.
The 4BT in my brother's '97 F-150 sure does dance around a lot at idle.
When he shuts it off, it looks like it gonna break the engine mounts and roll over in the engine bay.
However, it is smooth when above idle.

Over on the 4BTSwaps forums, there was a thread of posts talking about the vibration of 4BT.
One member had a 4BT with some factory counter rotating shafts in the oil sump that canceled the vibration. There were pics of this assembly.
Of course, I cannot find that thread. :(

[memphisjim]

25 mpg makes a wagoneer Great Googley MoogleyGreat Googley MoogleyGreat Googley MoogleyGreat Googley Moogley near a tree huggers car

[Mikel]

The 4BT in my brother's '97 F-150 sure does dance around a lot at idle.
When he shuts it off, it looks like it gonna break the engine mounts and roll over in the engine bay.
However, it is smooth when above idle.

Over on the 4BTSwaps forums, there was a thread of posts talking about the vibration of 4BT.
One member had a 4BT with some factory counter rotating shafts in the oil sump that canceled the vibration. There were pics of this assembly.
Of course, I cannot find that thread. :(
Your brother's idle is set too low. I don't have a tach, but the idle in my 4BT is probably about 800-850. I had it lower and it was VERY violent. Now it is silky smooth. If someone gave me one of those mythical balance shaft kits, I would not even consider installing it.

Start ups and shut downs are not bad either, not enough to be noticed. What motor mounts does he have? Isolators are important, but the geometry also plays a great part.

[Kuraki]

My experience with diesel is that the fuel economy savings generally comes when under a load, or with a small engine and a low RPM torque range. That comes from my 2001 7.3L F250 and an old VW Golf.

The F250 will give me 18 MPG unloaded on the highway. It will give me 17.4 MPG loaded with a 3,000lb trailer and a 5500 lb FSJ on it. A similar gas engine would probably be in the 17 unloaded and drop significantly with a load to 10 or less. My F250 is one of the fastest 8800 GVW you'll drive, do to an upgraded turbo and chipset.

The Golf wouldn't win any races off the line, but it would accelerate smoothly and was able to cruise at high road speed with low engine speed, and got nearly 50 MPG.

My goal with a diesel in an FSJ would be to split the difference in the two examples, to get a vehicle that has low RPM torque for crawling around, but can use that torque with a manual or OD transmission on the highway for cruising at low RPM. I wouldn't expect to, or try to, put something together for 0-60 times, but with a turbo I don't see why you couldn't replicate 360 performance and a much better highway fuel economy.

[maritimerCJ]

The 4BT in my brother's '97 F-150 sure does dance around a lot at idle.
When he shuts it off, it looks like it gonna break the engine mounts and roll over in the engine bay.
However, it is smooth when above idle.

Over on the 4BTSwaps forums, there was a thread of posts talking about the vibration of 4BT.
One member had a 4BT with some factory counter rotating shafts in the oil sump that canceled the vibration. There were pics of this assembly.
Of course, I cannot find that thread. :(

Some of this has alot to do with the general design of a diesel, to be completely honest the diesel engine isn't quite the optimum engine for an automobile because of this reason (not saying they arnt better that a gas engine tho;)). The way they are built they operate best in a small rpm range and at a specific rpm will vibrate themself apart (critical speed), that rpm range is different for every diesel and you need to stay away from it.
On ship we run our diesels very specific rpms and thats why they work so well for our set up. In a automobile you are consistently changing rpm so you have alot of problems with vibration, this is the reason why there are virtually no diesel motorcycles, but if you guys want your minds blown check out this http://thekneeslider.com/archives/2006/06/19/neander-turbo-diesel-motorcycle/ its a new way to avoid diesel's vibration issues. But there are things you can do to help dampen the issue but out right get rid of it is impossible. most of my knowledge towards diesels is for large slow speeds (think MAN-BMW 40ft tall engines), and mid speed engines (v12, v16 emd's, caterpillars) but iv played with a few highspeeds. They are way way better that any gasoline engine imo.