Sweet Spot Question?
 

I have heard drivers talk about the sweet spot on the engine and rpms matching up that would be the best for mpg. Anyone explain this in detail, and tell me how to figure up this on the truck I am buying.

370 gear
C-15 Cat 475 hp
13 speed.

Thanks.

Engine mfg will sometimes show a dyno sheet showing the torque,horsepower and fuel consumption on one chart. You usually want to run where the torque is the highest and the fuel usage is the lowest. On older C-15 's it should be around 1400 rpm. Newer ones seem to like to be a couple hundred rpm lower. Since you'll be doing some off road work I'd lean toward 1500.

Tire size affects the axle ratio choice too - what does this truck have? With a pre-2002 C15 wiith low pro 22.5s the sweet spot would be around 60 mph. With high pro 22.5s or low pro 24.5s 63 mph, and with high pro 24.5s 65 mph.

Where can I get the BSFC charts? I've never seen one. All I've seen are really vague charts.

"sweet spot" is usually the best compromise between fuel mileage and performance. As you go slower,the sweet spot will be less rpms. If you need to run 70-75, the sweet spot rpm will be a little higher.

If you "have' to run 70-75, you don't care about MPG.
:shock:

I get 8.25 MPG @ 60
8)

For some bizarre reason my company has been installing Qualcomms... We need those like a hole in the head :roll:

But I was looking @ my fuel millage... 03 C15 runs real good set @ 550 hp. I only run loaded one way... no back hauls... 3.6 mpg :shock:

And when it gets cold they run 24-7 idle @ 1200 all night...

is there a way to just look at the boost gauge, say driving where you don't build more than say 15 psi of boost while cruiseing at hwy speed, to maximize your mpg's??? :? :?

o.k. road ranger on your 8.25 mpg @ 60..... were talking big trucks here not pick up :lol: 's..

1995 FLD120 small sleeper single drive axle, flattop w/air deflector, pulling a 53' van w/20k Lbs in it. 11.1L Detroit S60 325/350 HP, 9SP O/D, 4.11 rear, 11R22.5 tyres. Tractor 14K Lbs, trailer 16K Lbs.

Worst I got was 7.25 MPG in the winter - before I added the air deflector, switched to synthetic oil, and stopped doing 65 mph. Part of the "bad" MPG in the winter might also be the 150 degree thermostat(s).

Unfortunately this truck is gonna become a lawn ornament come next week - company I was leased to lost another big account and somebody had to go.
:sad:
Pretty impossible to find a carrier that will lease a 13 year old tractor with only one drive axle. Oh well - I got it cheap and it's paid for itself in the 10 months I've run it. Just came back from drug test and physical for Ryder Logistics, hope they don't suck too much! Pay's pretty good, no weekends, I'll be making a couple hundred more a week and no truck to work on.
:) :sad: :) :sad: :) :sad:

Maybe if the economy ever recovers she'll ride again!
8) 8) 8)