Engine RPM/Vehicle Speed and gas mileage

[j_lutter31]

Not sure if anybody wants it but I'll put it on here for what its worth....

(Vehicle Speed) x (1hr/60min) x (5280ft/1mile) x pie x (Rim Size + (2 x Tread Width x Tire Profile)) x (1ft/12in) x (Rear End Gear) x (Tranny Gear) = Engine RPM

I ran this through a few times...My tires are 245/45 R17, Rear End Gear is 3.27 and I have an AODE with a final gear of .7, The final gear of a Tremec T56 is .62
I have also found that a Tremec 600 has a .64 and a Tremec 500 has a .68

At 70 mph, and my stock setup I am turning at 2073 rpm. If I were to only change the tranny to a T56, I would drop that to 1836.

Now I am assuming that this is the reason that aode drivers complain about gas mileage being in the upper teens and manual drivers can somehow manage to get in the mid 20's.....Let me know what you guys think

 

[toyman]

Now I am assuming that this is the reason that aode drivers complain about gas mileage being in the upper teens and manual drivers can somehow manage to get in the mid 20's.....Let me know what you guys think

That's part of it. The other factor is effeciency. The manual trans does not have the driveline losses that are characteristic to auto's. However, the differences would normally be within 1 - 2 mpg. I just recently returned from a one week trip of about 900 miles with a mix of city/hwy and crossing two mountain ranges at 4400' and 5300' in each direction. Total average mpg was 19.7. I expect this to improve as I tweek my tune.