Don't look over the fact that a lower RPM for any given road speed is going to put more load on the engine.....in some instances, it is counter-intuitive to lower the operating RPM. I wouldn't try (if it were possible) a 40 MPH overdrive shift.
Case in point:
At 55 MPH in 3rd gear on level surfaces, I will see a very low EGT reading. However, in 4th gear just to maintain 55 MPH will result in higher EGT. I'm not saying that it's burning more fuel in 4th. However, I just lost ALL of my boost-building and low-smoke moderate acceleration abilities since all of a sudden I'm running a lot less RPM. Less fuel at a faster rate or more fuel at a slower rate....it's your call I guess.
If you could find a way to run a 40 MPH 4th gear setup, it would probably be wise to tune in a 4-3 downshift that occurs at a decent speed/APP as well (like anything less than 10% APP). If your low boost fueling is too high and the transmission won't downshift until you're running a decent amount of APP, you'll get a ton of smoke, no acceleration, and a really hard downshift when it does occur.
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Tuning, PCM flashing, and burning chips for 7.3s since 2008. Repairing all aspects of 7.3L Powerstrokes for 25 years.
Eight 7.3L PSDs in the driveway including a 1994 Crown Vic and 1973 F100/2002 F350. Looking for the next victim.
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Wed, April 15th, 2009, 02:20 PM
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