I have a school project that i am working on, and the idea of this project is to design a fuel efficent car. I was woundering what increases in mpg can i see through changing the gearing. Going from like a 3.73 rear end to a 2.83? any advice would be great.

Science fair project? Are we talking all in theory or are you actually going to test it? What car, engine, transmission, and tires then?

Science fair project? Are we talking all in theory or are you actually going to test it? What car, engine, transmission, and tires then?


No it is a senior project for a technical school i am in. It is based on therory, but the baises of the project is the use of new technoligies such as the beare head, and zeroshift transmission to get better fuel econemy with out sacraficing performance. Both of these designs increase both fuel econemy and performance.
Its a v8 engine, so far based off the mustang. I am trying to use the horsepower increases to off set taller gearing to maintain the same 0-60 times and 1/4 mile times, but get better fuel econemy.

You will probably notice very little differnce. I changed the gearing in my truck from 3.73 to 4.11 and didn't lose any MPGs. I know that's a bit different than what you're doing, but don't expect much of a gain. Fuel consumption is decided by engine load more than it is by RPM. If you raise the gear ratio to 2.83, you will just have to give it more throttle to maintain the same speed. But... I read several articles about the beare head, and if it's as great with torque as it sounds like, you may get some MPG gain.

the beare head is about 40% increase in fuel efficency and mpg. i am just trying to shave mpg's every where i can.

In that case, gearing may help, especially with a V8. A few other tips that combined may give you a couple MPG:

Run the thinnest oil reccomended for the temperature (I have personally gone lower than what the engineers said, but if you do, keep an eye on the oil pressure guage), and keep it at the "add 1 qt" line. This reduces the power used by the oil pump and minimizes power loss from the crankshaft pushing through the oil.

Inflate the tires to the maximum on the sidewall. I have seen tires rated to 44 PSI that were over 120 PSI (highest my guage goes)... Not that I'm reccomending anything like that :biggrin:

There is a product called "energy release" that you may want to look into for all fluids.

Wash and wax the car. Rain-X all glass. Remove the antenna and tape over the hole. Tape over any unneeded openings.

Depending on the length of the mileage test (and assuming it's not against the rules), disconnect the alternator to reduce the load on the engine. If that is against the rules, replace the tail/brake/turn lights with LEDs. Every watt of power you reduce will shave something off the fuel used.

Depending on the belt routing, you may be able to bypass the power steering pump and/or other unneeded accessories. Just make sure the water pump is driven.

Make sure the alignment is dead-on.

run the differential slightly low, maybe 1 inch below the fill hole.

remove anything that you don't need... the rear seat, center console, carpet, trim pieces, the radiator fan (if there's no city driving), washer fluid reservoir, coolant reservoir. If it weighs anything, take it out. If it's a clear day, remove the windshield wiper arms. You could also remove the passenger side mirror, if allowed by law.

thank you for that, info i will look into that.

I am still looking for info on how much fuel i can save by using more conservitive gearing.