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Quote:

Originally Posted by mike3fan (Post 463461)

I have a 379 with 550hp w/13 speed tranny and 3.36 rears and I get 6.2mpg running max weight and running east of the Mississippi. I would prefer 3.55's so that cruising at 65mph would run a little higher rpm, currently I run about 1200.

You can try switching to Low Profile tires something like 295/70R225, if you don't already use them, next time you upgrade the tires. They spin 510-512 times per mile as opposed to 495 rev/mi with regular 22.5. That might help raise your RPM at cruising speed.

510 x 3.36 x 0.73 / 60 x 65 = 1355

1355 - that would be your RPM at 65 MPH with low pro tires that spin 510 revs/mi.

Mine is the opposite problem - 550 hp with 13 speed, 3.73 rears and 512 rev/mi low pro tires - I do 59 MPH at 1350 RPM; so I"m thinking of going back to regular 22.5 that spin 495 revs/mi and would let me cruise at 1350 rpm at 60 mph.

I agree with Kranky on tranny. Must have 13, 15, or 18. Don't split if you don't want. I don't know why you wouldn't. At least on top.
If you do and you know how to, it will save fuel. It's really not that hard to lift your foot off the gas to change gears.
3.36 gears good.

Mike, I have 3.55 and wish I had 3.36, wanna switch?

Quote:

Originally Posted by RostyC (Post 463538)

I usually fall between 5.5 to 6.5 mpg with my 359 depending on the load I have on. I've had more than a few tanks come out to 6.8 and once got 7 mpg. That's a B model Cat, 400hp, 18 sp, 3.90 rears. I stay at or under 65 mph.

I learned my lesson the first time taking it over 65 mph, I got in a hurry coming home from NC and cranked it up to 75 mph, I swear I saw gauge actually drop, anyway I got 4.5 mpg on that tank.

When it's time to rebuild it, I'd like to build it to six or seven hundred hp, should be able to get a little better fuel mileage.

now i know this may be a bad place to put this, b/c you guys are talking about the big boy toy petes with kitty cat motors in them... but here it goes.

against the grain, I got myself an 03 Freightliner Century 120. Detroit 430/470 12.4L, 3.36 rears, 13 speed, 11R22.5 tires all around. she revs 1350 @ 61.7 miles/hour. Fuel milage? 7.76-8. I only do 61 mph, unless it absolutely has to go... or if a slower truck messe with me... lol. The truck does go 75-80 np, but i have my wallet in mind too... now i had heavy loads, and the truck pulls them to the consignee just fine. not the first there, but just fine. I go a good 1200-1300 miles on a tank of 200 gal. (btw the truck is an old CR England truck)

So if you can bear the "FreightShaker" it will leave you with a lot more money in your pocket than a pete... and you can actually fit into the doublebunk condo sleeper. I sued to drive a 378 with TMC, and boy was the sleeper a hole in the wall...

My .02 cents I'm happy making a lot of money, and keping more of it... lol

Cheers

I appreciate all of your responses.

Quote:

Originally Posted by BoyNextDoor (Post 463647)

That is good advice, BoyNextDoor. :thumbsup:

Quote:

Originally Posted by BoyNextDoor (Post 463647)

I go a good 1200-1300 miles on a tank of 200 gal.

1,300miles divide by 200gals = 6.5mpg

Quote:

Originally Posted by mike3fan (Post 463670)

1,300miles divide by 200gals = 6.5mpg

You are obviously using the wrong calculator.

A truckers math calculator always comes up with the numbers needed to back up a story.:thumbsup:.

I had a 2001 387 w/ C16- 600hp, 18 sp, 3.36 rears on 24.5 lo pro. It got 6-6.5 mpg consistently pulling a reefer. It did a fine job running the midwest.

Quote:

Originally Posted by mike3fan (Post 463670)

1,300miles divide by 200gals = 6.5mpg

um... the tanks are 200 gal. never can use the full 200 gal though... more like 170-165 or so... at a 1/4 tank i can't fit more than 110 gal, so i figure the gauge is way off... but the milage calculations do add up on the ecm and on the hard fuel numbers.. lol

Quote:

Originally Posted by BoyNextDoor (Post 463674)

It is a little late to be changing your story now.

First it was............

I go a good 1200-1300 miles on a tank of 200 gal.

Now, it has changed to..........

never can use the full 200 gal though... more like 170-165

You should have quit while you were ahead. :lol2:

You don't understand what he said. He had two 100 gallon tanks on the truck, and could regularly get 1200-1300 miles. Keep in mind after the trip, his tanks weren't empty.