Posted by Charlie on Wednesday, January 10, 2001 at 3:11AM :
In Reply to: M37 engine and tranny combos? posted by Rod Glassford on Wednesday, January 10, 2001 at 0:00AM :
A 4 cyl 3.7-4.0L diesel in front of an overdrive 5 spd is a great upgrade to a M37, with either 4.89 or 5.83s depending on intended use, torque/hp vs. rpm curve of motor, 5th gear ratio and tire size. Hercules made a bolt-in kit with the NP420 (capable of about 58 mph with 4.89s and stock tires and 64 mph with 11.00R16s; mine goes 76 with 37s and Clark 5spd) but they're currently out of business. They may come back to life. A Perkins 4.236, nat. aspirated or turbo, or 1004 Phaser (optionally with turbo and intercooler, 4.0L, up to 307 ft-lb) will work well. Cummins' 3.9BT/BTA has ratings upt o 130 hp @ 2500 rpm and 330 ft-lb. They are coming out with 4 valve/cyl ISB versions of the 4cyl 3.9B with ratings up to 440 ft-lb! With the high torque ratings but low rpm peak clearly a tall overdrive is indicated, either a NV4500 (0.74) 5spd, even a NV5600 6spd (0.73), or a Ranger II separate overdrive between the bellhousing and NP420 (0.73). There are no pre-made kits for the Perkins and Cummins diesels, but they fit in the engine compartment nicely and leave 3-4 extra inches for overdrives or longer transmissions. A conversion should definitely include front disk brakes, perhaps power steering, tire upgrade and 4.89s unless no significant highway use is planned or if very large tires are planned. For highway use it should be geared so that rpms are 80% of peak (rated max hp) at 60 mph. Even a bit lower if torque is much over 300 ft-lb.
Charlie
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