Originally Posted by wingman139
I have a 350 Cat Diesel pusher running my 40" coach. I would like to know what RPM will give my best milage?:
I do have some experience in this field from spending 20+ years working on and driving our diesels, new and older. From experience a lot can be said for the age and technology used in any motor so let's assume that you travel a set distance at the same speed, first in 3rd gear, then in 4th.
You can see that the engine will turn more times in the lower gear. Each revolution of the engine will "consume" the same amount of air/fuel mixture. Therefore conventional wisdom says that you must consume more air/fuel mixture at the lower gear.
Now this being said, a lot of modern engines are getting smarter about feeding fuel so the assumption of a constant a/f mixture may not be valid. With intelligent fuel metering the mileage difference may be small. The biggest difference to fuel consumption is your rate of acceleration. If you like to feel some acceleration and take pride in your ability to get to 60mph you will see improvement by playing "old lady" for a while. However, your motor does do more work when doing 1200-1500rpms to 60mph vs 2500rpms to 60mph. This increased work MUST be reflected in fuel consumption.
McFarlin AZ, '05 Alfa SYFE36FD, Freightliner chassis, Allison 3000MH, Jeep wrangler toad, wife and 3 four legged co pilots, Cody, Toby and Sadie II