Diesel repower alternatives to the 4BT?

[mikkelborg]

It's been a little while since my last post, I worked on the truck all summer getting it back to stock and now I'm back at school going a little stir crazy and fantasizing about a diesel repower again. I was inspired to get an M37 by Cabell Garbee's wonderful website and the original plan was to find a 4bt and a ZF5 and essentially copy his set-up. Since then I have been pondering some other diesels and I have a few ideas that I'd like some input on.

First is the IH 6.9. Specs I found were 170hp @3300 RPM and 315 ft-lb @1400 RPM. I like it because it has more power but not so much torque that I'm worried about breaking things all the time. The relatively low cost of a 6.9 is also very attractive and it could be mated with a ZF5 relatively easily to give a top speed above 70 with stock axles and tires. Parts are relatively easy to get and it is mechanically injected. The downside is that is weighs 860lbs dry, some of that would be made up for by using the lightweight ZF5 with it's aluminum case, but I would definitely have to add an additional set of leaves to the front springs. I think the whole set up will wind up being about 250 lbs heavier than stock (more research required). I'm not sure how that will affect handling, but since it's a non-winch truck I believe I am within the limits of what the front axle can handle safely. My main concerns are weather or not it will physically fit in the engine bay and how I will cool it, I'm afraid the stock radiator will not be enough.

The other idea that's keeping me up at night is a Detroit power plant, I like the 3-53T a lot, but it is such a low turning motor that I would have to go overdrive transmission and different axle ratios to make it feasible. I would have to do the swap in two steps as I can afford it, engine and trans then gears later or visa versa. The real problem is that it seems like it will cost just as much as the Cummins conversion will.

I do want to keep the truck original in appearance, and I want to maintain everything in such a way that I can undo my conversion and throw the old flathead back in someday if I so choose.

What are your thoughts?
Thank you,
Collin

[Master Yota]

The Navistar 6.9 is a decent engine, and dimensionally identical AFAIK to the 7.3L. I'd go with the 7.3 over the 6.9, if for any reason that its newer and parts are still readily available. Another option would be the GM 6.2 and 6.5L diesels. Both of which should fit with minimal issue. The 6.2 cheaper and easier to comeby, and was a good reliable diesel for the GM fleet. The 6.5 was the replacement, and althought it made more power than the 6.2, the 6.2 is reputed to have a stonger (read: longer lasting) bottom end.

The 3b and 3bt diesels found in the Toyota LandCruisers would also be a good candidate if you're you looking for a robust, 4cyl diesel engine, that will tolerate a turbo, and run for several hundred thousand miles... They are available with 4spds domestically and 5 spds internationaly. In stock trim they have about the same power output as a stock cummins 4bt.

[Tanner]

Welcome to the world of M37...

I'm Cabell Garbee's buddy - my truck is currently occupying space at his house...

To address some of your questions -

IH/Ford 6.9/7.3? Heavy, wide, and you won't see 70 on the highway with 5.89 gears & feel safe driving it. You'll be turning the weak link - the NP200 transfer case - quite a few revs. Cabell swapped to 4.89 gears & is running Michelin 900x16 tires, and the ZF box behind the 4BT. Different injection pump spring as well, IIRC, to get a bit more RPM.

Cummins? Obviously, the 4BT fits the engine bay quite well. Since so many have been installed, you won;t be blazing new ground to do the swap. But the Cummins has a bit higher price tag, and it's a quality engine. Charles Talbert has a lot of experience with the 4B-series, and excellent knowledge on the Spicers 3053A Deuce transmission/NP200 t-case combo.

Detroits? Heavy, noisy, but interesting, nonetheless... they weigh more than the 4B-series Cummins.

GM 6.2/6.5? That's the path I've been taking, as have a number of other M37 owners. Cheap? For the motor, yes. Durable? To an extent - the typical issues with cracking blocks (in the main webs) have been written about all over the 'Web. Starters/glow plug relays/etc., all have issues on occasion. I've started the 6.2/Spicer 3053A 5-speed swap on mine a good while back, but the time to complete it hasn't always been available.

What's your budget & skill level? Are you capable of tackling the project mechanically, with welding/fabrication/wiring/etc., or would you have to outsource some or all of these skills?

On considering a project budget, calculate the cost of what you think it will be, then add 20%. Then add 25% again...

'Tanner'

[Josh]

what about Nissan's little 3.5L straight 6 turbo, or, a 3.7 M-B diesel from a newer liberty or grand cherokee?

[chris olson]

If I didn't already have a 4bt lined up I would be seriously looking into a 4BD1 Isuzu engine from one of those GMC W4 trucks

[Tanner]

what about Nissan's little 3.5L straight 6 turbo, or, a 3.7 M-B diesel from a newer liberty or grand cherokee?

The M-B diesel is computer controlled & costs more (in most cases) than even a Cummins. And the Nissan/Toyota/etc., foreign diesels often lack parts support in the US...

'Tanner'

[Josh]

true, but, they are also more powerful, quieter, and more efficient...

[Tanner]

If I didn't already have a 4bt lined up I would be seriously looking into a 4BD1 Isuzu engine from one of those GMC W4 trucks

The transmission limitation is the problem with the Isuzu 4BD-series - limited to a cable shifted Isuzu manual trans, an automatic transmission, or a hybrid adaptor to adapt the diesel to 'X' transmission... and the bellhousing pattern is not SAE -

'Tanner'

[Tanner]

true, but, they are also more powerful, quieter, and more efficient...

AND expensive... don't forget the expense portion and the hassle of getting the electronics to work in an older truck. No current way around it...

A $15k motor swap into a $4-5k truck often turns people off -

'Tanner'

[Josh]

Agreed. I have a tendency to oversimplify electronics, since I work with em every day. I went out of my way to put EFI and distributorless ignition on mine!

As far as the Isuzu stuff, what about an adapter plate? is the input shaft long enough to have a 1" thick plate made?

[Master Yota]

what about Nissan's little 3.5L straight 6 turbo, or, a 3.7 M-B diesel from a newer liberty or grand cherokee?

The M-B diesel is computer controlled & costs more (in most cases) than even a Cummins. And the Nissan/Toyota/etc., foreign diesels often lack parts support in the US...
'Tanner'

Ha! For once you guys might have to look north for parts. A delightful change from us up here always having to look south! These diesels really are not hard to get parts for. The nissan diesel was available in the IH scout, (I would make the assumption that an IH dealer can still get parts for it..). Also, don't forget that alot of industrial equipment, like toyota forklifts and such, used diesel engines... Start combing the industrial wrecking yards, and equipment depots and you'll be amazed at what you'll find..
The ford ranger also came with a small mitsubishi (IIRC) diesel in the early 80's... I belive the Dodge D50 also had a small diesel option as well.

The biggest issue I see with a diesel swap, (any one of them) is gear ratio vs. engine rpm at (a sufficient cruising speed) - say 55mph. The average overdrive transmission has somewhere between a 20 and 30% over drive from a 1:1 direct drive 4th gear. With the stock 9.00:16 tires measuring about 34" tall, and a 20% overdrive, your operating rpm in 5th gear at 60mph would be about 2930rpm. Thats too steep for my comfort level with a diesel. Plus, with that rpm, you cannot downshift sufficiently to pass or climb hills without first slowing the truck down as a shift to 4th gear at that speed would have the engine turning 3664rpm.

So now to change the diffs over to 4.89 gives a cruising rpm of about 3135 rpm in 4th, and 2508rpm in 5th gear. This would be liveable (tolerable?) to me but has now added another couple thousand dollars to cost; now having to redo both diffs.

Just food for thought...

[mikkelborg]

I'd like to avoid the least powerful diesels that are more or less direct replacements for the flat 6 because I am looking for a modest performance increase to make the truck more streetable. I personally don't care for the more modern engines with electrics, a little bit of roughness and a mechanical pump with a cable operated shutdown fits the personality of my truck. That's probably why I like the noisy smoke bomb driptroit so much.

I'm still hung up on the IH 6.9, I'll admit it. I do not intend to ever have the truck cruise at 70, I was just saying, flat out, theoretically, I could do it, plus a little. The stock steering setup and brakes would be just plain scary at that speed! At a more realistic, but still somewhat frightening 60 (keep in mind, I drove it at 55, once, for a few seconds, with the stock flat 6), I should be doing about 2600 turns with stock gears and an overdrive. I would be able to downshift to screaming redline at about 60 in 4th gear. I'd have to get the drive shafts balanced and rebuild my transfer case to be sure its in good shape. Are 4.89 gears a standard upgrade on gas V8 powered trucks that run at highway speeds or do they just run the drivelines faster? The main reason I don't really want to swap gears right away is the cost. I can get a good running engine with about 100,000 miles on it for around $800 and the transmission for another $100 or so. Luckily for me they are plentiful around here. Compared to a good 4bt swap I am trying to figure out how to do mine on a shoestring budget, keeping as much original as I can. I don't have the truck with me right now so I can't just go slap a tape measure on it. If I got crazy and bought one, does anybody know if the 6.9 would fit between the fenders without chopping them up? I'm not worried about getting to the sides of the engine easily once it's installed because most of the common maintenance issues are most accessible from the top, front or bottom.

Thanks you,
Collin

[Master Yota]

I ran a gas engine in my previous M37, a Gm305 with 4spd. combo and the rest was stock. Was a great setup - absolutley loved it. The gasser has the rpm band to run down the highway at 60 mph all day, and not be concerned with the 2900-3000 rpm at cruising speed. Parts are stupid cheap and easy to find, the stock rad would keep the engine cool, and it fit. I easily tripled the mileage and hp of the flat six, and almost doubled the torque output. It never broke any of the driveline components, and it was just plain fun to drive (which is what every truck should be!)

The engine width is the main problem with most V8 diesels, and its not so much how far the engine sticks into the fenderwell, but where the exhaust ports dump in relation to the frame rails. A small block Gm gasser with the "ram horn" exhaust will just fit between the rails and keeps the exhaust pipe installation fairly clean, simple and straight forward. Any engine wider than that will dump right on top of the frame rails if the manifolds point downward, which usually doesn't provide enough room for the exhaust pipe to meet the manifold. Now you're filling the fendwell with a set of headers. Doesn't do much for the look of the truck, unless thats the look you're going for... If the exhaust manifolds dump out the rear, they will point directly at the cab, still without the clearance for the pipe to meet the manifold... The other option is to raise the height of the engine so the exhaust will clear, that means the transmission must move upward too, which means alot of fartin' with the cab floor, or a body lift. Not a big deal if you like that sort of thing...

Swapping a diesel or gasser won't be anything terribly difficult either way, but the devil is in the details. If you're on a budget though, I'll guarantee the gasser will be cheaper and probably easier.

Hope this helps...

[98taco3]

One option to possibly look into is the OM617 Mercedes inline 5 out of a 80s 300D. If its new enough its already turbocharged. Dirt cheap to get ahold of, parts are definitly reasonable/completely available as well as put out decent power. They also have a pretty dang good RPM range stock. The injection pumps are modifiable for more power and the engines can take it. Might be worth a look, ive got a 85 300D that the engine may be sacrificed to the OD cause lol. Not a US made engine but would work. There is a 5spd manual available for it as well. Its been adapted into TONS of vehicles because of its low cost. Adapter plates have been made to mate it to a bunch of different transmissions. Not to mention they will run on whatever you put into the tank, Multi fuel M37? Heck you could find a good lower mileage one with transmission in the 500-1000 dollar range...

[Tanner]

The Mercedes OM617 motor - while great in a 3600lb car - would probably be stressed in a 6000+ lb truck. I've owned 4 M-B diesel cars, both turbo and non-turbo.

The engine was rated in Turbo version at 3.0 liters/ 5-cylinders -
125 PS (92 kW; 123 hp) @ 4350rpm
245 N·m (181 lb·ft) @ 2400rpm (at best - most specs say 170 lb-ft)

There is a Colorado outfit - http://www.4x4labs.com - that was/is offering a $1000 kit to install a 'GM' manual transmission behind the Benz motor.

What transmissions? For now, they say SM420, SM465, NV3500, NV4500, NV5600 manuals...

The basic adapter kit will include the 4×4labs specific adapters- engine adapter plate, a custom flywheel and pilot bushing adapter. You will be responsible for off the shelf parts (GM clutch, GM pilot bushing or bearing, starter, etc.)

And juicing up the OM617 is not that easy; there's not much room in the pump to 'turn it up', and they don't respond well to performance mods like the later (but lesser quality) OM606 turbo 6-cylinder 3.0 motors (avoid the 3.5 motors like the plague) which were known for head/head gasket/etc., issues.

'Tanner'