3.42 ratio vs. 2.64 ratio on cascadia

Well 70 is going to have the motor on roughly 1600 with direct. Not that familiar with the C12 and what RPM it does its best thing at. With a 13, in 12th at 70 mph, one is looking at 1350 RPM, roughly. Being light, that is a better way to get things done.

 

I think that many people don't realize the benefit of running in direct. In a manual transmission, all gears except direct involve sending the torque through different gears from the input shaft to the output shaft, with corresponding parasitic losses. In direct, a sleeve locks together the input shaft and the output shaft, with no, in theory, parasitic losses. However, as most modern transmissions are constant mesh, all the gears are spinning anyway, so I wonder how much better mileage you really get in direct.

 

It is hard to quantify that. Like most other fuel saving measures, they really only start to add up the more things are done. I am not sure a person running a truck at 75 mph with the aerodynamics of a brick would notice a difference. But running in direct, the trans temps stay way cooler. While there may be other gears turning to some degree even in direct, they are not generating nearly the heat as either the under or overs do. The 18 spd I have in front of 2.64, and primarily run in 16th direct, temps stay pretty darn low on the trans, even on a hot summer day under hard pulls. Only when I go outside of direct do the temps then come up more. So if the trans is generating lower temps running in direct, there has to be a corresponding decrease in parasitic loss by running in direct, and that would imply more efficiency.

 

You would think. As far as aerodynamics, my 379, the fan never came on even in the summer, with ac on, (running down the road, Stuck in traffic, different story), except pulling a hill. A Volvo I drove had the fan on figuratively all the time. Would I have gained what I should have lost to the Volvo because my fan didn't come on?

 

Well, the fan coming on more frequently is obviously going to make a difference, and make and model have something to do with that. A fan being on a lot is going to eat into fuel economy. My 2013 FL Columbia glider, with it's tiny little nose, the fan doesn't cycle any more than most any other truck on the road, even the ones with a front end the size of a house. It all depends on the motor and how much cooling is required, and of course, how fast one is going and how much air is being pushed thru there already. Mine is pre-egr, so it is not having to cool EGR stuff which makes a significant difference in how much a fan would have to cycle.

 

My Detroit was pre-egr, and the ISX in the Volvo is egr. Mileage was better in my truck.

 

Cowpie in 16 th what speed you generally cruise at?

What are your plans? Will you run your glider until it dies or are there plans for a new one soon?

 

I generally run 1425 - 1500 RPM in 16th which puts me at 62 - 65 mph. I plan on keeping this truck for a long time. In the immortal words of Garret Morris on Sat Night Live..."it's been berry berry goot to me".