M939 Powertrains

[ClassicTVMan1981X]

Since the standard M939 series powertrains seem to lack on low-end torque given that the Allison MT654CR transmission is only suited for engines producing up to 625 lb/ft of torque when used for heavy truck applications (hence the old-hat Cummins NHC250 for the A1s, or the Cummins 6CTA8.3 240 hp for the A2s), have any of you ever changed out your MT654CR to an HT754CR so as to accept the Detroit Diesel 6V92TA engine (330 hp / 963 lb-ft) or the Cummins L10 (up to 320 hp / 1000 lb-ft) engine?

Already, the Cummins NHC250's advertised torque rating of 686 lb/ft exceeds the MT654CR's heavy truck application torque rating of 625 lb/ft, so therefore the right torque converter ratio must also be specified. That engine had been discontinued as an on-highway engine back in 1975, as turbocharging was becoming the norm. Cummins made a 230-hp turbo version of the NTC which produces 800 lb-ft of torque.

~Ben

 

[doghead]

What would you use for a transfer case?

 

[4XDesign]

What would you use for a transfer case?

Transfer case is divorced. The only thing that would impede installation is if the transmission was too long to allow the short shaft to be installed in between the transmission and transfer case. Unless you are referring to the fact that the transfer case may not stand up to the additional power. In which case someone else's input will be needed. I say you should go for it I have had many different powertrain options in vehicles with divorce transfer cases.

 

[162tcat]

I think he is referring to durability issues with the transfer case. They already fail in low with the stock powertrain so bumping it up to 300+ hp and 1000+ tq would probably destroy it if a guy wasn't careful.

 

[Suprman]

I believe a few people have swapped the engine with a cummins 400 with good results and no drivetrain issues.