Diesel in your Dodge

Charlie Aarons [email protected] Diesel Engines

The question of re-powering a M37 or Power Wagon (B1PW to WM300 type) with diesel is often discussed. I have put Hercules diesels in a 48 B1PW and a M37, both with 5 speeds, and also years ago a Perkins 4.236 in a Toyota Landcruiser. I also have a factory diesel 77 BJ40 Landcruiser with an aftermarket turbo and other mods, and a 88 F350 crewcab 7.3 with many expedition mods (see www.ford-diesel.com), so I have some experience and ideas in the field.

There is a rule in diesel conversions "don't over-power". Overly ambitious diesel swaps tend to be very nose heavy, chew up front tires and axles, steer and brake poorly, and freqently what you end up with is a lot of torque but poor rpm capablility from a big slow engine. Good performance can be extracted from some surprisingly low horsepower packages.

In the old Dodges, the prime issues are length, and preserving the appearance and off-road performance, while improving highway performance and economy. The critical length is the back of the radiator to firewall. That generally restricts choices to 4 cylinder diesels. The only common exception is the GM 6.2/6.5 V8. It would be a very tight fit in a PW and a fairly tight fit in a M37.

Boyce Equipment, a well-known surplus drivetrain outlet in Utah, may be able to supply a 6.5/flywheel/bellhousing/adapter/Spicer 3053A package. The 3053A is a 5 spd with ratios=5.90, 3.10, 1.70, 1.00, 0.85. There a re many 4cyl diesels in the world. For the weight range of the Dodges the types with displacement on the order of 1L/cylinder are good. Look for displacements in the 3.7-4.1L range. These generally are " modular" derivatives of sixes that range from 5.5L to 6.2L.

Virtually all automotive diesel mfgs have engines in this size range. My list is by no means inclusive, and more power to you if you find a Fiat tractor engine that is 4.0L, 4cyl, 600 lbs, 120HP at 3100 rpm turbocharged, and 270 ft-lb, and it fits. Another fitment issue is not having to move the transfer case. That of course depends on transmission length. with the stock bellhousing in the stock location, up a 15" (front flat face to rear flat face) gearbox will work with only driveshaft shortening. And clearing the front axle by having a rear sump oilpan. Et cetera. Using an engine from a non-vehicular application requires caution.

Generators and pump engines are usually de-rated and may require new fuel injection pumps and even injectors, not just a pump turn-up. Stationary engines usually have up-outlet exhaust manifolds. marine engines have water cooled exhausts. Tractor engines have heavy very large oilpans, rigid mounting, different flywheels and bellhousings, etc. Below, HP/torque ratings will be listed like: 80@2800, 193@1400, or simply 80/193.

Hercules: The 3.7DT (108@2800/231@1800)and DTA (125/268) are fairly light (only 25 lbs heavier than flathead, 125 lighter than Perkins and Cummins) and BOLT-IN for M37. Easy installation in PW. Available with GM, Ford and old Dodge adapters to bellhousings (bh), no SAE#3. Hard to find used.

Cummins: the big six WON'T FIT!. The derivative 4BT will fit. It's highest torque rating is 130HP@2300, 122@2500, 327 ft-lb@15-1700. many other ratings. Adapters for many bhs including modern Ford, GM, Dodge, SAE#3. I don't know if it'll bolt to the old Dodge bh but the low rpm characteristic absolutely requires and overdrive. A NV4500 will bolt to it. Expensive new, all diesels are.

Perkins: Old line British/world-wide mfg. 4.236 is 750 lbs, 80HP@2800, 193ft-lb@1400. 4.236T=110/240. The 1004T is a 4.1L modernized version with about 260 ft-lb. A good stong reliable engine, but the 5" stroke causes vibration which requires careful flexible motor mounting. The 1004T may have better balancing. Perkins prices may be slightly cheaper per HP than Cummins.

Detroit Diesel 3-53. Snake River 4X4 knows about putting these in M37. Requires 4" front lift, also 2 more front leaves (weighs 900 lbs with aluminum block, 1000 lb w/iron block; don't get a used Al block). SAE#3 and GM truck type bhs will work, m,aybe others. N version is 102HP@2800, 205 ft-lb@1800. Noisy, 5-10% less efficient than direct injection 4 strokes (it's a 2 stroke). May also fit into PW, they are tall but not much longer than the others.

Isuzu 4BD1: 3.9L, turbo version also available.  Where these Japanese engines might be a bargain is a take-out from one of the forward-control trucks they reside in along with the slick synchromesh transmissions, 5 speeds, 5spd with splitter (10spd!) or 6spd (with 6th overdrive).

Nissan SD33T: 3.3L six turbo, 100HP@4000/180 ft-lb@2200. Too weak, might physically fit. Not a good choice.

Toyota Landcruiser diesels: the sixes have good power turboed but are too long. The 4s up to the 13BT (3.4L, direct inj., turbo, 120HP@3400, 210ft-lb@2200) are borderline on power, would easily fit. If I were to have a 13BT fall into my lap in good shape I was ordered to drop it into a PW, I'd be very careful about the gearing (leave it at 5.83, use 5spd with 0.845 5th, 2650 rpm at 60 with 11.00R16s) and consider an intercooler and turn up the pump another 10%. Mercedes makes a 4L 4cyl diesel. Bellhousing adapters could be a problem, unless it's SAE#3.

John Deere makes a good motor in the right range. Generally speaking you need a motor in the 4L size range, 23-2800 rpm peak hp, or higher; a side or down facing exhaust outlet, a rear sump, bh hookup that'll bolt to something appropriate, a engine weight of about 775 lbs or less, a fan to back-of-block length at least 2.5-3" shorter than the back-of-radiator to firewall distance. Changing applications and buying parts like flywheels, having pumps, turbos and injectors rebuilt can add up real fast.


I have a saying: "Gearing is everything". Well, practically. It's in my opinion about 50% more important than cubic inches. A lot of Americans think otherwise. Most all of these diesels have what's called "poor rpm flexibility", compared for example to the 4.4L V8 gas engine in our BMW 540i. It pull the car in 5th from 25 mph to 155. No diesel will do that.

Generally, most diesel re-powers need 4.89 gears. An exception would be a high gear that's pretty steep (like 5th=0.73 in the NV4500 or 6th=0.72 in Ford/ZF 6spd) in conjunction with tall tires (Michelin 11.00R16, 538 rev/mile), and a relatively high revving motor (6.2/6.5=34-3600, Toyota 13BT=3400). A low revver like the Cummins 4BT, even with 4.89s, NV4500 and 11.00s will top out at 78, cruise at 2100 at 65: perfect.

5 speeds The "most optimum" 5spd I've found for the old Dodges is the NP540. OD ratios: 6.06, 3.31, 1.81, 1.00, 0.82.. The only problem is that there are no OD version input shafts as spares and therefore a broken NP540 (the input shaft of an OD truck transmission is the weak point) is gone. If you find one in good shape, try to make it work. for example, you can switch cases to match bolt patterns, or sometimes modify bhs to match transmissions. About 160 lbs.

An easy conversion trick is drilling and tapping new holes in the bh to match the transmission, milling out the center hole in the bh to match the bearing retainer, modifying the input shaft tip (like machining it down to match the pilot bushing) or getting a different pilot bushing (they make "extended pilot bushings" that shove in a certain way, then abut against a considerably larger diameter, and have the machined female part actually sticking out of the flywheel a bit to compensate for a too short input shaft - just so long as the splined part allows the clutch disk to free float a mm or two), and getting a special clutch disk made up with different splines in the hub than usual for the application. A couple of warnings: Don't let a machinist reduce a fat input shaft to a smaller size to match a clutch disk. Get a special disk made up instead, retain the strength. If you have a diaphragm type clutch, make sure you have the heaviest springs. Getting a job all done and then having the clutch slip is a pisser. Third, consider a "solid" (spring-less) clutch disk. Clutch disks have been known to break. The Hercules may only put out 125HP, gee whiz, just like a Dodge Neon. But 268 ft-lb would twist a Neon into a pretzel and can break 10" clutch disks.

Clark 280VO. There's about 15-20 different Clarks, now called Eaton Fuller FS4205s that are 5spds. The 280VO is the only overdrive version. Ratios: 5.98, 3.50, 1.86, 1.00, 0.80. A bit weird. 15" long, the max when bh is in stock location to keep xfer case un-moved. Big, strong, heavy. 208 lbs. Performance Gear in Lumberton Mississippi builds them, he does ALL the machine work necessary on input and output ends to suit your whims and needs, also on your bh to match. Whatever you need for $2000. also available with more civilized ratios with 5th direct like: 6.99, 3.78, 2.12, 1.28 or 1.48, 1.00. 5th direct would be good with 6.2/6.5, 4.89s and mongo tires like Michelin 14.5R20s (43.4",  2550 rpm at 65). He'll build the trans to match just about any bellhousing.

NV4500: The new popular all synchro 5 spd, older GM only ratios 6.34, 3.44, 1.71, 1.00, 0.73, new GM and Dodge ratios 5.61, 3.04, 1.67, 1.00, 0.74. Main problems: too long, about 20-21" in 2WD version, that means even a 4cyl engine must be crammed up against radiator to have any chance of fitting. Expensive, but starting to showup in junkyards. Expect to pay $1000 for low mileage used, $15-2000 rebuilt (?+/- core?). Bolt pattern requires special bh, too wide to re-drill most normal light duty truck bhs. Special bh isn't cheap either. NV is working on 6spd 5600. problems staying in one piece behinds ISB Cummins (is that a surprise? It's probably the input shaft! Why don't they use a 6th direct trans like the Eaton Fuller 6306A and use 3.08 or 3.21 or 3.55 gears?)

ZF 5 and 6 spds (Ford diesel trannies): I don't know if a 7.3 would fit in a M37. It would be interesting. Cummins has an adapter to the ZF. Despite its' aluminum integral bh design, it's a strong transmission and also comes in 2 to 6 ton European army trucks. But like the 4500 it's too long to retain the divorced transfer case in the old Dodges.

A way around the transfer case problem, for more money: Use a married NP205. Use either a WW2 Dodge axle with centered diff, buy a 14 bolt GM Corporate axle from Boyce for $1050 with 4.88 gears, or convert the NP205 to have an offset output. Some parts from your NP200 might help. The NP205 has been put together this way "by mistake" in the past, I don't see why it's impossible to do it intentionally. Then you can use anylength transmission you want and have the same strength transfer case. Oh Boy, Cummins 4BT, ZF 6spd, NP205, 4.88s/Detroit Locker! Just use your newer tires on the front, 2/32"wear difference compensates for the difference.

Spicer 3053A. The deuce-and-a-half 5spd, only the multifuels. ratios: 5.90, 3.10, 1.70, 1.00, 0.85. For SAE#3 bhs. Cheap, available for $400 in good running shape. But 16.5" long, probably will squeeze in with the shortness of most of the above mentioned engines.

I don't know of any other overdrive 5 speeds available in North America. Watch out for the transmissions hooked to the Japanese diesels in the forward control trucks. Toyota has/had in the Dyna series a "SuperShift" 5 and 2 = 10 speed, all synchro. Makes up for low torque, quite a bit.

Separate overdrives: 1) Ranger II overdrive, built by Advance Adapters, fits between bh and 4 spd (standard Ford, GM and Landcruiser bolt patterns). Ratio = 0.73 and direct, manual shift. Most 4spds are 10-12" long, so that's a total of 17-19". So OK if the motor moves the bh rear face 4" forwards - quite possible. About $1500. 2) Gear Vendors (GV) overdrive. Planetary, I don't like planetary gears, but allegedly quite strong, 30,000 lb gvw rating. Designed for motor homes. Works only in 2WD, designed to fit behind transfer case. Electric shift with little switch on gearshift lever. Usable as splitter in 3rd as well. Ratio = 0.78 and direct. Price $2000. 3) US Gear overdrive. Ratio 0.80/direct or 1.25/direct (underdrive) It has 4 small counter shafts. Also electric shift, generally fits between transmission and transfer case, not usable in stock-like M37/PW setting.  

That's it! I'm sure I'll think of more right away, though. If the serious reader has questions feel free to e-mail me at [email protected]. Or call me at 907-349-8673 on weekends, remember Alaska is 4 hrs earlier than Eastern, 1 hr before Pacific. Or after 7PM weekdays. Or at 907-257-8117 and leave a message if I'm not at my desk. Things I would like to see: Cummins 4BT into an old Dodge Perkins 1004T "      "    "      " More Hercules powered PWs, not just mine Some creative re-power with a takeout from a Japanese forward control truck, like a 3.7L diesel with a 10spd

Don't forget, if you do these things to make a truck that'll cruise in the fast lane at 65-70 mph, be sure to add front disk brakes and consider power steering. And bias ply NDs just won't cut it those circumstances. Michelin radials, even hyper-aggressive XL treads, are way safer at speed. They'll wear fast at those speeds but they won't blow out (as long as they are properly inflated, maybe std. highway pressure + 5 to 10 psi) and control is decent, even in rain. I said decent, not great.


Dated  : April 22, 1999 at 20:13:20 Subject: Re: Diesel Conversion

You have a AT3.4? Lucky you. The length of the motor fan to back of block must be at least 2-3" LESS than the back of radiator to firewall distance. The Spicer 3053A takes an SAE#3 bellhousing and clutch, if the Cummins has that you're fine. Since the Cummins is a six things might be tight lengthwise, the case length of the Spicer is 16.5" (measure to be sure). 5.83s with the Cummins would yield 2650-2850 rpm at 60 mph, depending on tire size (9.00-11.00R16). Good for hilly/mountainous terrain. With 4.89s, rpms would be 2400 at 60 with 9.00R16s. The motor has peak HP at 3600, peak torque at 2000-2400. Charlie

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