I don't know all that I should about the bigger transmissions, but listen to this
I have seen and talked to a guy who built a KW with a 12V71 Detroit with twin turbos, about 625 HP. He owns a trucking company, and I trust he is somewhat knowledgeable in truck components and strengths. The transmission he used is a Roadranger RTO14613P, good for 1,400 lb ft of torque.
He was concerned that any less transmission would not hold up.
What is that Mack transmission rated for, I am thinking it is not quite enough.
About the auxiliary transmission. The stoutest one Spicer made was a 1241, a 4 speed twin counter shaft unit good for about 1,200 lb ft of engine torque. Perhaps even that is not enough for your engine?
The largest Roadrangers are good for 1,650 lb ft of torque, available as a 13, 15, or 18 speed.
It may be a good idea to talk to several knowledgeable transmission service guys and even someone at Eaton Fuller for recommendations as to what transmissions will hold up.
I just don't want to see you spend money on transmissions that self destruct. That could be inconvenient to say the least, as there are not many bigger trucks out there, and a tow could be spendy.
Grigg
