What gearing does my 88 Gt have?

I bought my 88 GT a few months ago and was told it has 3.73's. I have no way to tell as this is my 1st mustang. I went out today and drove the car documenting some info... let me know what you guys think....

2nd gear at 30mph 2400k rpm
3rd gear 50mph 2800k rpm
4th gear at 50mph 2200k rpm
5th gear at 50mph 1500k rpm

Thanks
 
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Gear Ratio Calc

3.55 is what I get.


But that way depends on how accurate the tach is and your speedo....which aren't very accurate after a gear swap.

Better method is to mark the driveshaft, and jack up the rear tires and count how many rotations for 1 turn of the rear tires. 3.5 turns would be 3.55. 3.75 turns would be 3.73, and 3 and a quarter turns would be 3.27
 
Either 3.27s or 3.55s, but it's hard to tell because we don't know your tire size or how well your speedometer is calibrated.

Count the number of driveshaft rotations like Mustang5L5 says, but I suggest turning the wheels 10 times (have a helper turn the wheels, while you watch the driveshaft). I can tell you from experience it's hard to tell 3.27 rotations from 3.08, and 3.55 from 3.73. 35.5 vs. 37.3 is much easier.

Or you can remove the differential cover and start counting gear teeth. You probably need to change differential fluid anyway. :D