Detroit Diesel, 06 515 HP fuel mileage

mine got 5.5 before the delete 6.2 ish after 05 classic 13 3.55 thats running 70ish

 

My tweaked 12.7 gets 6.15 on average running 65 mph, and thats with my 10 speed and 3.70 rears and 22.5 lp tires and that is running 1500 rpm or so and thats in my 379 pete.

 

Well, I was getting 4.5 mpg and then had the overhead run, now i'm regularly seeing 6.25 to 6.5....But, also, I changed the way I drive it, the 14L likes to be run high in the rpm range. Ive been running 1,850 is 60mph in 9th and I get better mpg's there than 1350 in 10th (60mph)......The best mpg's are at 67mph in 10th gear at 1550 or so.....I've been lugging it all last year and this year realized it likes to be run above 1500 (up to 1850).....

 

I agree mine is happy around 1550-1600 rpm for best fuel mileage as well.

 

Funny you guys mention this mpg thing.

I've recently bought a 2016 WS with a ddec4 14L. Before this new truck I've always had cats. So I've been driving this new detroit the same as all my cats . Cruising at 1350-1500 rpm .

After some trial @ error I've found it pulls better and gets better mpg if run little higher in the rpm.1500-1700.

Basically it likes it about 200 rpm higher then the cats . Less or no downshifting, better mpg . I guess it only stands to reason the shorter stroke detroit...

Not a bad engine , pulls just as good as any cat I've had just got to keep the rpm up .

 

Yeah, it pretty much took me a year to realize I was lugging the engine trying to keep it in the green on the tach, just did 550 miles on Friday at 60 mph in 9th gear (1850 RPM), got 7.35 mpg.....ran same run at 60 mph in 10th at 1350 and avg was 5.5mpg....lesson learned!!!!!

Seems to me with 3.55 or 3.58 gears the S60 14L is ideal for a 13 spd....

 

I compare driving my 12.7 Detroit to riding a 2 stroke dirt bike. Keep the motor wrapped up in the Rpms and she pulls great. Lug the motor down and it's a dog. Keep it above 1500 rpm and she's right in the power band.

 

So the 12.7 is also an RPM freak of an engine?

 

Ya mine is for sure. At 1500 rpm I can lay into her and she will get up an go.