[josh stuckey]

Which manual gearbox is most likely to run in the vicinity of of 2750RPM at 55-60MPH?
I'm currently running a 351C C6 with 3.5 gears and would rather have a manual when towing a large boat. I don't go offroad it is primarily a tow vehicle, 2.5t boat.
I think a Top loader would go close to this range but can it be matched to the NP 208 Tcase I have. I like the top loader from past experiences, and would rather not have a granny gear.
Let me know what the possibility's are.
Thanks in advance.

Josh

 

[havack]

In top gear, all boxes, besides OD boxes, are 1:1. Your thoughts should center on what you want for first gear. really low? Normal? High?

Tire size will effect how fast the engine turns in top gear. My .8:1 OD runs 2100 in 5th on 33's. My fourth (1:1) is about where you are wanting.

 

[Rockfrog]

As stated above all trannies available to mate to your engine will be 1:1 in top gear with the exception of the OD trannies (SROD, TOD, AOD, M5OD ZF 5spd ....) so a 3 spd will have the engine spinning the same as a 4 spd will. You are targeting the wrong area ... to change the RPM's your engine sees in top gear you have to do one of three things (or both) -
Install an OD trans (if you have one drive in fourth instead, OD's not really meant for towing anyway),
Change tire size, or
Change the axle ratio's.

With 3.50's in the axle, stock tires, and 4th gear you should be running at 2230rpm's @55mph ... upgrading the axle gears to 4.10 should put you where you want (2613 @ 55mph .. or go 4.27's for 2721 rpm @ 55)

I have an excell spreadsheet that calculates rpm values for any speed you enter and and charts it according to tire size and axle ratio. if you want I can e-mail it to you. :shrug