What Gears do I have?

[CranberryCoupe]

I have searched and cannot find an exact answer to my question. I bought my mustang and the guy before me did no know if the gears had been changed. I have a 93 5.0 manual. I drive it to work on the freeway for an hour on the occasional nice day and it just seems like 80mph at 2500 rpm is a little high or it could be that it has no cats and is just that loud. Can you guys tell me what ive got back there?

thanks,
Brian

 

[RatStang]

Jack up the back of the car and put it on stands. Mark the inside sidewall of your tires, secire the other from rotating. Put a lateral line on teh driveshaft. Rotate the onseure wheel one complete revolution while counting the number of times the driveshaft rotates.

 

[CranberryCoupe]

Thanks...... I feel kind of stupid I couldnt figure that one out myself

 

[NIKwoaC]

Jack up the back of the car and put it on stands. Mark the inside sidewall of your tires, secire the other from rotating. Put a lateral line on teh driveshaft. Rotate the onseure wheel one complete revolution while counting the number of times the driveshaft rotates.

Isn't that going to make the driveshaft turn half the amount that it should? If you make sure both rear wheels make one full revolution, count the driveshaft turns, that is the ratio. If one wheel is fixed, the ring gear is turning at half the speed of the rotating wheel, via the spider gears.

 

[XStanger]

Sounds like 3.73's to me.

 

[TRWXXA]

You left off some important information... Like what size tires you're running. And you need to be very accurate in your other figures, or any estimation of your gear ratio will be off.

For example, if you're running 26" tires, and your RPMs are exactly 2500 @ exactly 80mph, then you have 3.55 gears. If the RPM is more like 2625 @ 80mph, then you'd have 3.73s.

If the gears were swapped and the speedometer wasn't corrected, then you can't use speed and RPM to figure out the gear ratio. The stock tachometers can be terribly inaccurate too.

BTW... Here are the formulas:

Tire Height (in.) = Tread Width x Aspect Ratio ÷ 1270 + Wheel Diameter

Rear End Ratio = Tire Height x 0.002976 x Eng. RPM ÷ Trans. Gear Ratio (0.68 for a '93 5-speed) ÷ MPH

Do the wheel rotation method, but turn the wheels 10 times and count the driveshaft rotations (get a helper for this). It's easier to tell the difference between 35 and 37 rotations (3.55 or 3.73 gears) verses 3.5 and 3.7 rotations. Trust me.