The Stovebolt Site Forums The Parking Lot Big Bolts Isuzu NPR drivetrain swap?

I'm wondering if anyone here has looked into swapping a 4 cylinder (5.2 liter) diesel engine and transmission from an Isuzu NPR into a big bolt? Apparently, these come with double overdrive 6 speed automatic transmissions. A little searching around on the internet shows that NPR's have rear end ratios as low as 5.85, so it seems these might be ideal match for AD trucks with their 6.17 rear gears.

I looked at some, and they could be good for a complete drive train swap, generally narrower axles than most trucks, which will help for an AD.

Personally, I would not use one, it's hard to explain why, but basically because they are imported and look like it. Also, they are not real powerful considering the effort involved for a conversion, really nothing special.

They would probably make a reasonably useful conversion, but again nothing spectacular.
If you really like the Japanese diesels I say go for it, but don't do a conversion you are not really excited about. It's a lot of work, so spend your time and money on something you will really like when done.

Grigg

That's good advice!

Ripcord I think the gear ratios offer some performance clues. The tires installed stock on the NPR are likely shorter than the originals on your big bolt, meaning the effective difference in ratios might not be what you think.

Short tires and a deep ratio rear make me wonder if the motor needs a lot of leverage to get a load moving.

If so that's not a good thing if you plan to use this truck as a truck. And its even worse if you plan to use it as a hot rod.

Its difficult to say if a modification is a good idea or not without first having a clear understanding of your intended result. How do you want to use the finished truck? How do you want it to perform? I'm sure you have some idea the answer to these questions, but without knowing your answer its difficult for us to give meaningful comment.

The NPR might be perfect for your intended use and you aren't the first one to suggest it as a donor. Off the top of my head I can't think of one I've seen finished, but I don't know if its because no one has tried, if no one has suceeded, or if I just haven't been looking in the right places...

I dunno, every NPR I have ever been around could barely move, let alone pull any weight. Dependable tho.

I've got a diesel conversion in the works, but it's sort of a long-term project. I've got four of the Onan/Cummins 120 HP turbo diesels that were used in UPS box vans stashed away. They're approximately the height and length of a Chevy 292, and probably a hundred pounds or so heavier. These engines are HP rated at 3,600 RPM, so they're definitely not typical low-speed torquer engines.

The really nice part about using these engines- - - -the bellhousing UPS used is the same as a late-50's Chevy V-8 truck unit, with a hydraulic clutch cylinder on the passenger's side. A SM-420, or anything else with a similar bolt pattern hooks right up, and it uses a standard 12" Chevy medium-duty clutch. The front motor mounts have the same spacing and width as a 292. UPS trucks were set up to use the 292, the Ford 300, or the Onan/Cummins interchangeably, with just a swap from diesel to gas or vice versa in the fuel tank. Whatever replacement engine was available got used as required. Most of the over-the-road trucks got the diesels, with the gas rigs used for around town. Cummins couldn't supply enough replacement engines, so UPS scrapped that erngine and retrofitted something a little more plentiful about 10 years ago. One of my friends bought a semitrailer load of them in running shape at scrap iron prices, and I ended up with a few of his leftovers. They're complete engines, crank pulley to bellhousing, and most of them still have power steering pumps mounted. The first one's going into a F-350 flatbed, and my 59 Suburban might get the next one, along with a 3/4 ton IFS to match the GMC Dana 60 rear axle that's already in there.
Jerry

We have some of the NPR's where I work. The turbo lag is ridiculous. Once they get going they top out around 80 and they are a high revving engine. With a load of approx 11,000 lbs (this includes the weight of the cargo bed and cargo) combined city and highway mpg is around 8.

Wow my first day here and I can already contribute...

As it happens I own an 93 Isuzu NPR that I use as pickup truck. It won't set any land speed records but it does handle anything I've put on the back. At one point I was towing a flat bed trailer with 54 chevy wagon on it plus a full load on the bed. The nice man at the weigh station let me go thru, I was still 130 lbs. under the trucks limit of 14,000#. I towed this from Philly to Northern, NJ. Averaged just a tick over 10 MPG but did have to slow down to 25 MPH up some hills.

I am putting together a '34 1-1/2 ton panel and have considered using an Isuzu diesel. I have run across an adapter kit to allow the use of a 700R4. Most of the NPRs in the bone yard have bad trannys. The engines cost about $2200 for a complete rebuild (cylinder liners, etc.) From everyone I've spoken to, the little diesel is one of the most reliable.

Charlie (in NJ)

I had an NPR in my business and although it topped out at 71 mph and took a while to get there, in 180k miles it needed a set of brakes and an alternator and that was it. It also seemed to carry anything put on it's back. For one trade show 60 miles away, it carried a John Deere 4310 tractor with loader on it's back and a Mahindra 2810 with loader on the trailer and a big commercial mower. I don't know how heavy it was but I know it was well over.