How much would my gas mileage increase if i put in a higher gear ratio in my truck?

I have a 3 speed auto transmission and when it goes out i might put a 4 speed auto transmission would that increase gas mileage by a good bit. I drive a 1978 GMC Jimmy that gets 10 miles a gallon.|||Not unless the fourth gear is overdrive, which most four speeds aren't. Most three and four speed transmissions are a 1:1 ratio in their final (high) gear so the engine is turning the same RPM's, for any given speed, in both. The only thing the 4 speed does is give you closer gear spacing so the engine doesn't have to rev quite as high between shifts. Gas savings would be minute if any at all.|||sure the extra gear lowers the rpm.|||Your mileage would not increase. You would just get there faster|||no it would not.... the final ratio is the rear end ratio the four speed transmission in fourth is one to one as is the three speed.. you can change the ratio at the rear or put on larger tires that is all you can do... also do not run the lower gears to long..|||These days i say one thing to people "hydro assist" doubles the gas millage for ANY vehicle, and VERY EASY to install.


See: http://www.jeffotto.com/affiliates/sr.ph鈥?/a>





If you are a certified mechanic you can install it without the void of any warranties.





Hydro Assist took my Subaru Legacy 2.5 4 Cylinder from 23 Mi per gallon, to 63 Mi Per Gallon Fuel Consumption.