Whats the deference between these two gear ratios?

Question

Ok I have A 1994 F-150 with a 3:55 in it and a 1996 F-150 with a 3:08 in it. They both have E0D4s in them. Whats the difference is it that big? And y does the 3:55 seams to pull better and gets 7mpg better than 3:08? Thanks!

Answer 1

I think you mean your trucks have an E40D (transmission) - which is different than the differential which houses your gears. You are right, the 3.55 will have a faster rate of acceleration but a lower top speed. The 3.08 will accelerate slower but have a higher numerical top speed. In either case, your F-150's will not be going fast enough for the top speed difference to come into play

Technically, the truck with the 3.08s should get better gas mileage - as the motor will be at a lower RPM at any given mph - for example if the 3.08 geared truck is at 1800 RPM at 70mph, the 3.55 geared truck will be at 2100.

The fact that the 3.08 truck get that's much worse MPG is surely a sign that the engine needs a tune up.

Answer 2

Well the 3.55 will pull better because it is a shorter ratio which is more likely to keep the truck running closer to its peak torque range.  It is interesting that it gets better mileage though as the 3.55 runs at a higher RPM at the same speed.  It is possible the transmission is geared differently as well which could account for the better mileage and torque.