Well I finally got around to inspecting my rear end. I found the casting number first, but didn't bother recording it. I already knew I had a H150 just by looking at it, so I didn't see the point in deciphering the casting number.
The stamped number was much harder to find, but I eventually cleaned off the crud in the right place. It revealed a "CL620". So now I know my truck can be "SLOW" and "SLOWER". Or as I'll prefer to call it, "TORQUEY" and "TORQUIER".
So I ran a few calculations:
SM420 w/ 7.50R20 speeds
So it looks like I'll top out at 51 MPH if I run the engine at 3000 RPM. That's fine if I'm on a backroad highway, but we have a lot of straight, flat roads where I think a higher cruising speed would be in order. I know I'd have to give her plenty of time to come up to speed, of course. But if it's straight and flat, I think even a 235 ought to be able to muster up enough power to go 60 MPH when traveling empty.
So, after some research, it seems that a NP-540GO might be the ticket; especially if I upgrade the engine at some point. I ran some more numbers with that as an option:
NP-540GO speeds Looks like that gains me about 11 MPH with all other factors kept the same. This all assumes that the 551 revolutions per mile that I dug up for the 7.50R20 tires I have is accurate. I'll have to wait and see.
