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View Full Version : OT - Isuzu NPR / GMC W3500 fuel economy



whateg0
09-24-2006, 09:45 PM
Does anybody here know what kind of fuel economy (hwy/town/avg) the 3.9L Isuzu turbodiesel gets with a standard trans and whatever is typical in those trucks for rearend? The reason I ask is that I saw a 4cyl Cummins in a Jeep in an issue of Diesel Power magazine, and thought to myself that would make an okay engine for a small pickup, or a full-size where room was needed more than pulling power.

Dad's '92 Dodge Cummins/5 spd gets around 21MPG, so if the 4cyl is much better it might make a good motor to replace the aging 302 in my truck, which gets a very lousy 13.3MPG hwy, or 13.3MPG in town.

Thoughts?

Dave

edit: and I know that loaded/unloaded, box/flatbed, etc. will afffect it. I'm just trying to get an idea of whether it is better or not. I guess the closest thing would be an unloaded flatbed.

NOS
09-24-2006, 10:24 PM
If yer talking about the 4 BT Cummins, it's probably an industrial engine that would typically be used in a large fork-lift, or small loader for example. The 6BT Cummins is the engine used originally in the Dodge P/U's and larger loaders and fork-lifts. I doubt that the 4-BT would satisfy you. FYI most "yard-dogs" made by oskosh and others to move semi trailers around a lot, use the 6-BT. The 4-BT is used in alot of big gen-sets, and small heavy eqpt. normally. I have an NPR but it's a gasser and gets about 10 mpg loaded to 9K. as a welding rig. Hope this helps.

whateg0
09-25-2006, 02:46 AM
If yer talking about the 4 BT Cummins, it's probably an industrial engine that would typically be used in a large fork-lift, or small loader for example. The 6BT Cummins is the engine used originally in the Dodge P/U's and larger loaders and fork-lifts. I doubt that the 4-BT would satisfy you. FYI most "yard-dogs" made by oskosh and others to move semi trailers around a lot, use the 6-BT. The 4-BT is used in alot of big gen-sets, and small heavy eqpt. normally. I have an NPR but it's a gasser and gets about 10 mpg loaded to 9K. as a welding rig. Hope this helps.

I'm not sure which engine it was. I know it was a 4cyl. and it was out of a FedEx (I think) delivery van.

Thanks for the reply.

Dave

Y2K
09-25-2006, 09:33 PM
Hang on until next spring when I will have a rebuilt 3.9 (4cyl) installed in an 83' Chevy 1/2 Ton 4X4. According to my sources, it's possible to get up to 28MPG. ???????

My engine came in Frito-Lay delivery van with TH 400 trans, all mounts, radiator, elect fans and all the necessary pieces including 1000CCA battery!

NOS
09-25-2006, 09:54 PM
Dan, if it was an automotive engine, It would probably be fine. Call yer local Cummins dealer and have the "CPL #" ready. This can be found on the aluminum data plate riveted to the left front accesory drive. (front cover where the fuel pump mounts) Also the "pump code" can be found rivited to the injector pump. With thease 2 #'s,,,Cummins can tell ya exactly every nut and bolt, rpm, H/P etc. the engine is built to, and set for. If it was a fed-x truck engine I imagine that ya probably oughta try and get the transmission as well! Most automotive tranneys won't stand the torque even the 4 BT is capable of. Another thing to consider is the rear ends ratio. Gassers run at higher rpms than diesels do and with a 4.10 ratio for example yer diesel would be screamin at 55 mph. A 3.70 rear-gear or less would be better. Tell the Cunmmins SALESMAN the tire size ya want to run, CPL# & PUMP-CODE,,,and he will be able to tell ya exactly how it will act, and answer all yer questions. Ask for an engine salesman! Hes the only guy that can tell ya what ya need to know. Trust me on this...I worked for "Cummins Intermountain" here in Vegas and was a Cummins Factory Certified Mechanic/Machineist tho I bet its expired by now. Come to think of it,,,I bet my engine certs with Caterpillar, and welding certs with Freightliner and Navistar probably have expired too.:confused: ;) Call Cummins!

whateg0
09-26-2006, 11:45 AM
Wow! This is great! This is exactly the information I was after. Y2K, keep us posted on the engine swap. Who knows if I will ever get around to doing something like that, but if I do, I will definitely try to learn from your experience.

NOS, thanks for the great info. If I do a swap of this sort, I will likely try to retain all of the drivetrain, even if it means a few extra pieces have to be fab'd. I am thinking of getting a late '80s or early '90s GM truck for this. We'll see, though. I figure if the engine is enough to move a big box van down the road, it should be capable of moving a pickup, and the trucks some of these motors come out of have up to a 12k GVWR, so that shouldn't be an issue, I don't think.

Thanks again for the info.

Dave

NOS
09-26-2006, 10:50 PM
Yer welcome!

Masher Mfg
09-27-2006, 11:26 PM
I'm in the middle of a 4BT into a 77 Chevy 2 wd 3/4 ton.

From what I've read and experienced, a 3 speed auto trans isn't a happy state of affairs. If you gear the rear for a good top speed , the low speed acceleration suffers. If you gear for acceleration to top suffers.

Early Dodge diesels used a 3 speed auto with 3.08 gears. This combo is rather slow when pulling out from a stop. ( I drove a 89 towing a 20 ft box trailer for about 500 miles ) The Dodge 6 gets away with the high gears because it has more torque ) Once past 20 MPH the performance is great. In all reality, when towing a trailer you really don't need top speed to be beyond 75.

The B series motors have a 2500 RPM red line while a typical 350 Chevy motor can rev to 5000. This limited rev range makes more trans speeds vital.

All of the external 6BT stuff will bolt to a 4BT. I'm using a Dodge 4 speed auto, flywheel and adapter. It's looking like the 3.73 gears in the rear will work just fine with this combo.

Take a look at 93 and up Dodge motor mounts, they are large castings with rubber bushings. The 2 and 4 wd mounts have different offsets and might help your situation.

You can get a balance shaft kit for the 4 BT, It will make the motor smoother but it _WILL NOT_ fit a 2 wd 73-87 Chevy truck unless you are willing to raise the motor 4" and raise the body 4" as well. BTDT. A 4wd truck has a much smaller crossmember and plenty of room and is likely it will fit.

Add a intercooler, it will make more power will little effort. I'm using the 93 and up Dodge unit. All of the Dodge turn up tricks can be added to the 4, a few minor tricks can make a 4 run like a early 6. The appeal is the 4 motors are much less $ than the 6 stuff and likely to have less miles. I paid $ 1000 for a mid miles ( sub 100,000 ) 4BT, Chevy adapter, 4 speed manual and rear end from a bread truck. Bought 2 for this price.

Lastly, go to the Turbo Diesel Register web site, they have a Cummins conversion section of their web site.

Oh yea, others with a 4BT in a full size pickup report mid / high 20's MPG for fuel.

whateg0
09-28-2006, 09:41 AM
I've looked at the diesel web sites. One of the sites had almost nothing of interest on it, only dmax stuff. I'll look at the recommended site. If I do this with my current truck, I'll have to check into availability of brackets and such, and maybe fab some stuff, which I don't mind - makes it custom.:D Otherwise, I am also looking at older Dodges right now. After all, I wouldn't mind having a different truck. I'll probably try to stay away from the autos. I was kinda thinking about a Dodge 5spd manual. Also not worried about the balance shaft, unless it significantly adds to the life expectancy, but diesels are robust enough that vibration is just an annoyance to some, and acually a turn on for others.:rolleyes:

Thanks again for all the information. I'd still love to see some pics when available.
Dave