Thinking out loud

Vincent Vignola · July 22, 2020

Then add bigger heat sinks lol. GM did that with the updated l5p for the 2020 hd trucks. The fan on the new engines is much larger. The ford also got better mpg than the gmc because the l5p diesel had more load and wasn't in it's efficiency sweet spot as much. Having a quicker rear end brings the gears in the tranny closer together.

newdude · July 22, 2020

1 hour ago, Vincent Vignola said:

The main idea for me asking is for a gear splitting ratio. Tfl truck took a gmc 3500hd Denali crew cab up the ike with 30,000 lbs. They did the same with a similarly optioned f350. The ford had the powerstroke and a 10 speed auto, but it also had a 4.55 rear end iirc. The ford frankly performed much better than the gmc going up that hill, like 8 mins opposed to 11. The split speeds in a transfer case arent much more than a second transmission, and one can engage the low speed in 2wd if they wanted. I remember seeing 2lo on some transfer case designs, and this system wouldnt be much different than a semi trucks gear splitting box.

The idea is to make the rear gear ratio much longer to keep the efficiency up for low load cruising, and in tow/haul mode the transer case would kick down into low and give a much quicker effective gear ratio.

Ford uses a 3.55 or optional 4.10 gearing with the 10 speed and the powerstroke.

Your Ike times you quoted are wrong. You are looking at the gas engine times at 8min (Ford) vs 11min (Chevy). This is a whole different issue there, as GM didn't keep the 4.10 with the 6 speed like they should have, instead switched to 3.73. GM can easily remedy the gas HD with either the 4.10 gearing going back in it, but in reality, it needs the 10 speed with the 3.73 gears.

On the dually 30,000lbs shootout, it was 11:47 for the GMC, 10:20 for the Ford, so just over 1 minute slower. Both got 2.4 mpg. The Ford even had the 3.55 gearing. Ike gauntlet is an extreme scenario. Most HD diesel owners won't experience such a test of their truck. Cummins did 11:32.

Having to engage a low range would just make things messy. These aren't big rigs moving 80,000lbs. If GM wants to experiment, they either bump the power (probably going to happen) or they try 3.73 gears again with the diesel like they used to have with the 6.6 from 2001-2019.