in most of the engine books
they have graphs showing that for
gasoline engines of the SAME POWER
a turbo engine will be equal to a NA engine at about 75% load
but superior in fuel economy both below and above 75%

VW says that its direct injection gasoline engines it calls FSI
are most efficient when at a mild boost of 2 to 4 psi
at piston speeds below 1300 feet per minute,
and it seems that Saab, Volvo, Subaru and the new twin turbo BMW I6
have highway cruise at about this engine MAP and piston speed

Most diesels benefit from modest turbo boost
similar to the brake specific fuel consumption graph
for a 1.9 TDI diesel shown below:



notice the 197 grams per kw-hr near the torque peak
in a range from 1500 to 2000 rpm
where power works out to about 50 to 70 SAE horsepower

197/608 = 0.32 lbs per hp-hr

 

With what a cummins, and 4x2, regular cab? Geesh, that is insanely good. 55, can't do that on the back roads... SHNOOL <--- can't keep his foot off the gas, loving on that exhaust note!

 

you're wrong and right.

turbos help air intake, so they increase your volumetric efficiency, meaning you can take more advantage of the volume you have in your engine (an engine is typically not able to fill up all the room in the cylinder with air). turbos actually often increase your volumetric efficiency to ovre %100, meaning they actually compress the air into the cylinder before the valve closes.

Yes this increases horsepower, but when you're not using the increase in efficiency for horsepower, you are using it for added fuel efficiency.

Engine performance for horsepower and overall fuel economy generally go hand in hand. if you have more torque from your motor, it's not working as hard. Sure you can use it to accelerate harder, or you can use it to make accelerating at a slower pace easier.

diesels are mostly more efficient because diesel fuel has a higher energy density, and diesel engines can run at a higher compression ratio (higher thermal efficiency) without knocking. The turbos are actually added to diesels to make up for the lack in power when compared to a gas motor because diesels turn much slower. So yes, the turbo is used primarily to increase the horsepower, it also adds efficiency when you don't need the power. we do a LOT of turbo development, and most of it revolves around just getting a rated power that we want, and then increasing efficiency as much as we possibly can.

<takes nerd hat off>

 

15.1 city 20 hwy 2008 quad,4x4,auto,4.7

 

I say if someones getting around 15 city, with a 3rd generation 4.7 or 5.7, thats a good deal. I know the sticker said for mine 13 20. 12-14 is alright. Lower than that I say someoone needs a check up lol

 

Yea, and 4x2 should get slightly better mileage than a 4x4. Oh! My mileage actually dropped by 1-1.5MPG with the addition of my T.R.E. TW Series cap -- must be creating a he77 of a lot of vacuum behind me.

 

JUDGING BY YOUR PICTURE YOUR CAP IS TALLER THEN THE CAB CREATING A BIGGER HOLE IN THE AIR MEANING YOUR TRUCK HAS TO PUSH MORE AIR TO GET AROUND

 

I've got between 15-17 mpg with mixed driving. I've never took a trip with my truck so I don't know what the highway mpg could be.

 

the original post said he kept the revs below 2000.I live over 3000.never good for gas milelage.i think you are supposed to try to stay around 1750 for gas milelage.
does anyone know if the red line is 5800.
afraid i have hit that a few times

 

He has 06 2500 QC 4X4 Cummins and yes I have seen the math and what the computer says it right on.