What gears do I have???

blkelvs · 09-14-2005, 06:52 PM

So I bought a used 2000 Mustang GT, and if definately has aftermarket gears but I am not sure if they are 3:73's or 4:10's, the guy I bought it from didnt know either, as he was the second owner... All he knew was that the speedo was off by 10 percent. So here are some RPM's at speed with the 10 percent correction, which I am sure is pretty to close to correct based on the radar speed checks on the freeway...

At 70 mph (Speedo says 77) I am taching between 2350 and 2400 RPMs at 80 mph (Speedo says 88) I am taching 3000 rpms.

Any one have any idea?

Thank You

blue00gt · 09-16-2005, 03:34 PM

The speedo reading is proportional to the gear ratio.
77/70 = gear ratio/3.27
So if you don't have a SpeedCal or something that would mean your gear ratio should be 1.1*3.27 = 3.59.
So it actually sounds like you have 3.55s based on your being 10% off. Anything steeper and your speedo would be off more. I have no idea why anyone would swap in 3.55s though - 4.10s all the way!!
Are your back tires stock height?

09-14-2005, 06:52 PM	#1
blkelvs Registered Member Join Date: Apr 2002 Location: Mt. Shasta Ca. Posts: 3	What gears do I have??? So I bought a used 2000 Mustang GT, and if definately has aftermarket gears but I am not sure if they are 3:73's or 4:10's, the guy I bought it from didnt know either, as he was the second owner... All he knew was that the speedo was off by 10 percent. So here are some RPM's at speed with the 10 percent correction, which I am sure is pretty to close to correct based on the radar speed checks on the freeway... At 70 mph (Speedo says 77) I am taching between 2350 and 2400 RPMs at 80 mph (Speedo says 88) I am taching 3000 rpms. Any one have any idea? Thank You

09-16-2005, 03:34 PM	#2
blue00gt Mustang Addict Join Date: Jan 2001 Location: McKinney, TX Posts: 1,294	Re: What gears do I have??? The speedo reading is proportional to the gear ratio. 77/70 = gear ratio/3.27 So if you don't have a SpeedCal or something that would mean your gear ratio should be 1.1*3.27 = 3.59. So it actually sounds like you have 3.55s based on your being 10% off. Anything steeper and your speedo would be off more. I have no idea why anyone would swap in 3.55s though - 4.10s all the way!! Are your back tires stock height? __________________ Strike down the unroadworthy! 2000 GT Atl. Blue: '03 Cobra motor - 465rwhp/473rwtq, T-56 6-speed, full MM TA/PH & tubular K-member suspension, Saleen body, 17" Torq-Thrust II's, M/T ET Street radials, and lots more '94 Rio Red Cobra: All the bolt-ons, 3.73s

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