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Old 07-11-2012, 10:18 AM   #17 (permalink)
Just some guy
Join Date: Jul 2012
Location: MN
Posts: 8

Truck - '08 Ford F350 XLT 4wd 4Dr
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Originally Posted by amdown View Post
If i would shift ta 2500- 3000 RPM and press acelerator pedal about 70%, then it feels like I am going on drag race So there is no point off reving engine up to 2500 - 3000 when presing acelerator pedal up to 30%

All I know that driving at peak torque would kill turbo and engine a lot faster, because at that RPM engine is developing peak torque and all engine components are at maximal stress. (I am also a car mehanic and i know what I am talking about). In my lupo I already had rebuilt my engine, including new turbo.

vw also suggests that shifting early is better for MPG. And as I know, construction of PD TDI engines and new bluemotion engines are not so different either, both have direct injection and VNT turbos.
Shifting will be engine, drivetrain, terrain dependant. Anyone who says not to shift the 7.3 PSD at peak torque, when under load, doesn't understand diesels. IH and Ford recommend a shift range w/ the 7.3 and the 6spd to occur between 1800-2000 rpms, right where the peak torque is. It doesn't kill the 7.3 and it for sure wont kill the turbo.

I had an 02 7.3 PSD and I short shifted that 8k truck all the time unless I was loaded. 18 mpg for a 8k brick wasn't bad but I did well due to shifting around 1500, just under the peak torque.

OVERSPEEDING a turbo is what kills them, besides lack of oil. A stock 7.3 turbo will live forever under factory injectors and factory tuning going 250-300k miles as a pulling/hauling vehicle. However, a simple "chip" add on creates extra boost that, over time kills the turbo due to repeated over speeding, and even for the aftermarket GTP38R Garrett Ball bearing unit, they recommend not to exceed 40lbs of boost.
I know that aftermarket HO Precision and Bullesye turbos die from being oversped.

FWIW, having owned two large vehicles there is a variable that people some times forget and the 14mpg semi on this forum should be a reminder to all:

1) Keep rpms as low as possible w/o lugging the engine. It takes fuel to make revs. He's running 1200rpms @ 55. A member on another forum I frequent is getting 24mpg hand calc in his 8800lb F350, dynoed at 700Hp. He got the hwy #'s by using 3.31 vs the factory 3.73, keeping rpms low.

2) Aerodynamics. Factory cars will never get super duper mileage from the factory for now since the public as a whole doesn't want bullet cars. This also falls back w/ RPMS, it takes more fuel to push your barn door or even your small door through the air, the faster you go the more fuel that is burned.

3) Parasitic loss, poorly lubricated drivetrain components, sticking brakes, etc.. I noticed a 2 mpg drop recently and i had a caliper sticking. Fixed it and things are normal again.

I come here to pick up some ideas and its interesting to see the innovation that is made.
I truely miss the 50mpg, in stock form, mid 1980's honda civic. People get exicted about a 30 Honda accord, oh how we've forgotten what was not only possible but what was.

Really, if you are a mechanic and have experience w/ cars and diesels. You should feel comfortable and know to take advantage of the torque the TDI provides. Shift just above the lugging point so you're not having to go beyond what your current throttle position is and still provide enough power to continue at your desired rate of accelleration. I'd say there is no magic # as I mentioned before there are plenty of variables to discredit a set RPM #.
08 F350 6.4 PSD IDP Tunes

Last edited by powerlifter405; 07-11-2012 at 10:34 AM..
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