at what rpm is your peak torque?

 

Yeah I hear ya. I felt the same way when I started to drive this truck instead of an N14. I used to downshift at 1400 until I read the little plate on the M11 engine that says it makes peak torque at 1200 rpm. So I thought I'd try letting it lug down to 12. Rpms drop to 1200 and then she just hangs there. Then I'll usually drop 2 gears to 11th and that gets me back to 1400. If you go by feel or sound you would down shift before 12 that's for sure. But it does hang in there a while.

 

1045 crank HP and 3470lb-ft torque, C-15 bridge MBN with goodies, 6.2-7mpg running midwest-west coast.

 

Cleveland Brothers Cat just reprogrammed a few of my trucks...with what they said was a "heavy hauler" program. It basically boosted the numbers across the board. MY personal truck...which I drive for MPG gained between .3 and .5 MPG, which Ill take a 1/2 mpg any day. So yes I believe that all else constant, more power when driven smartly, does=mpg...atleast in our case. I cant explain it, and wont try

 

The heavy haul program is just that, a 2300rpm program with a wider power curve, it doesent drop off after 1700rpm like a stock 550-600hp 2100rpm program does, this is only available for 70pin ecm trucks and up. The older trucks with 40pin (1LW, 6TS, 5EK, 5DS) didnt have this option.

If you are looking for more power a 7CZ 600hp C-16 ecm flash will gain about 150hp over a stock 550, if you play with the FLS and FTS some you can get close to 250hp over stock ..... CAT will not let you change those though, you need to know someone..... Also set your injector trim codes to 6999, thats good for another 50whp, and you should be able to get it done at a CAT shop as its a customer parameter.

 

They probably modified how much emissions it puts out too. Increase NOx = better fuel mileage due to higher peak combustion temps.

I think that's what a lot of these "programmers" do. They don't just increase the fuel rate, but modify a few things, that result in more HP as well as MPG.

 

my peak torque is at 1200 rpm; but Cat recommends lugging the engine to 1100 before downshifting on hills. they swear these engines were designed to take it. and it works.

 

Well, my fuel mileage still leaves much to be desired. Fueled up at Flying J near Laredo, TX the other day ... The magic number for the past 960 miles has turned out to be ... 5.89 mpg! Only 0.19 better than before. I drove like an idiot - 57 mph all day with the engine turning at 1,300 rpm. I still had lots of pulling power and low rpm wasn't an issue. Half of the way I had a wind blowing into the rear of the trailer; without the wind the fuel mileage would probably be lower.

So, despite low profile tires, full air roof deflector, increased horse power, free flow performance muffler, extremely low road speed (57 mph) and engine speed (1,300 rpm), LOAD WEIGHT continues to be the most important factor affecting my fuel mileage. Give me 10,000 lbs - I'll do around 7 mpg. But as soon as the load weight goes over 35,000 lbs - the fuel mileage drops below 6 mpg. HEAD or CROSS WIND is another biggie... kills mpg at once. I talked to a Cat shop mechanic about this and he said, "Try running at 1325-1350 RPM next time you have such a heavy load. You might get a better fuel mileage". Hm... I'll give it a try... The one thing I'm curious about is if I get this poor mileage of 5.9 mpg with 43,500 lb load running 57 mpg - how much worse would it be if instead of my 2004 International 9400 I had a Freightshaker XL or 379 Pete? 4.5 mpg?

 

Don't forget about the "seasonal" change. 10%, or even up to 15% loss in MPG, is pretty much normal, in a winter time....

 

I averaged ~6.8 or so last summer. My last 3 fills were 6.2, 5.9, 5.7. This is 80,000 lbs gross south on I81 and 33,000 headed north. I think there is more blending as the winter goes along.

I'm not convinced that the aero trucks are a guaranteed mileage maker. Some of those things are heavy pigs. And they all have high rise bunks. I think a flat bed guy could get the same mileage in a 379 as he could in an aero truck. He might have to drive slower though.

I'd like to buy an old mechanical 359 flat top and give it a try.