[VAC] Re: Towing With A Manual 5Speed Transmission

[Dr. Gerald N. Johnson, electrical engineer]

I WISH first gear was as much as 6:1. It isn't. The best in a Ford 5
speed is 4.72 in the 3/4 ton, only 3.92 in the 1/2 ton 5 speed
transmission. I figure its important to have an overall ratio (first
gear and axle) in the range of about 20:1 for starting loads. Hence the
4.10 axle gears with the 3.92 first gear in my F-150 that seems to work
well. At least that's 16:1. Choosing the axle ratio is a compromise
between starting and cruising speed because the range of ratios in the
modern transmissions isn't as wide as I wish. But for the small V-8 in
my '98 F-150 faster engine speeds have not proven to cost gas mileage
and certainly gets more torque to the ground. The computer lets it run
richer above 2500 or 3000 rpm. The added torque can be felt as it winds
up besides the torque peak is a higher speed. HP is rated at 4600 rpm.
Since its on overhead cam engine there are no push rods through the
intake side of the head to restrict breathing. Whether it will run
210,000 miles remains to be seen. At my current rate of driving that
will take another 18 years to find out.

Greater engine speed for the same torque load at the wheels can mean
lower pressure on the engine bearings and probably longer life, but only
if the inertia loads from the higher speed don't exceed those from the
output torque loads. I'm not sure I appreciate Ford's insistence on 5W30
oil. I'm inclined to prefer a 15W40 for a stronger oil film in the
bearings.

I posted extensive thrust computations on this list or its alternative
last year. December and January a year ago as I was making the shopping
and buying decisions to replace a broken truck.

Gerald J.



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