Into the @m*m^2

[JimT]

Follow your boost and pyro gauges and pick your gears accordingly. keep the boost as low as possible. If you can roll down the road in top gear with 5-10psi of boost and rpms down around 1500 then go for it! If you need more psi then drop down a gear and try again. Even pulling most grades can be done with less then 20psi boost, the trade off is speed. Basically try to use the highest gear that allows you to use the least boost pressure. You'll find you get the best overall fuel mileage along with the least stress on the engine. If you can be flexible with your speed then you can find the best rpm/psi for the conditions. If you have to maintain a certain minimum or average speed then you'll be limited in what you can do.

Took me a while, but I recently got down to using 5-10psi of boost, max. Only occasionally up to 20psi for a steep grade. With the gearing in my tractor it keeps me around 58-62mph, sometimes down around 45mph, but the results for fuel usage have been great. I started simply by trying to keep the boost under 20psi, which was difficult at first. Then I worked my way lower and lower over time.

I pull flatbed with a mid-roof tractor so wind plays a big factor in my fuel mileage too. It actually has a bigger impact than gross weight, for me. When the wind is howling through my doors I can see up to a full mpg loss along with higher boost pressures for the same workload.

I actually had a scare recently because of my newer habits. I started climbing some minor hills that I pass regularly and my speed dropped fast, multiple down shifts, could barely make it up the hills (local roads, not highway) at 20mph. I started freaking out, thinking something was wrong with the engine or maybe the turbo stopped working... The turbo... Then I looked at my boost gauge and realised why I didn't have any power... I was subconsciously limiting my boost to 5-10psi like I would do on the highway... Needless to say, once I pushed down on the pedal a little more I made it up the hills no problem. I had gotten so accustomed to barely pushing on the pedal that I didn't even realise what I was doing.

It's gotten to the point that I rarely hear the turbo spooling up anymore. Every once in a while I actually have to purposefully push down on the accelerator to make sure the turbo is still working and can actually produce boost pressure above 22psi. It's really weird.