Why do you Cummins guys want more gears

ShinerBock wrote:

4x4ord wrote:

ShinerBock wrote:

4x4ord wrote:
Would 3.73 gears give you what you want in 9nth? Or if you could get 3.0 gears you’d have the towing rpm you want in 8th. 3.0 x 4.6 would still provide you with an overall lower 1st gear ratio than your present 3.42 x 3.75.

Then what is the point of having more gears if you can't take advantage of lower rear gear ratios? I have a 68RFE, not an Aisin. I also have 35 inch(technically 34.5) tires which are needed for obstacles at the ranch and deer lease to keep from bottoming out.

The ideal towing rpm for me is between 1,600-1,900 rpm(preferably @ 1,800). I know your ideal rpm is different, but according to Cummins and the BSFC map of the 6.7L, that is the sweet spot depending on load.

I think the BSFC map you posted shows the sweet spot (the dark blue) ranging from about 1500 to 2000 rpm and at a minimum of 600 Nm of torque output which I think indicated about 50% engine load. That map was for a less powerful engine and still would require working the engine hard enough to be down at about 9 mpg at 1800 rpm to enter into the sweet spot. At 1500 rpm you’d be working the engine hard enough to enter the sweet spot (700 Nm) while getting about 10.3 mpg @65 mph according to the map. So that BSFC map indicates that 1500 rpm would be a better towing rpm than 1800 for a 15k rv. (Which again is for a less powerful engine than the 2021).

Nope, not for my year model. The sweet spot was between 1,600 and 1,900 according to my BSFC maps. It starts out at around 42% of max hp(145 hp of 250 max hp at 1,600 rpm) at this rpm, not 50%. Max hp for this range is around 250 hp at 1,600 rpm to 307 at 1,900 rpm.

I believe you are thinking of the new models which is the efficiency series engine and not the high output which would have a smaller sweet spot so you really can't use it in your math since you don't have the map for the high output engine which has a lower compression ratio than the efficiency engine along with other variables.