Trying to figure out gearing...

[dmontzsta]

My friend has a 93 LX 5.0 with a Tremec TKO 3550. He bought a set of 3.73 gears, but was wondering if the car already has gears. It spins about 2,750-2,800 rpm at around 75mph. This seemed a bit high to me, which is why I questioned it and told him it might already have gears.

The motor is stock with MAC LT headers bolted to a non-catted H pipe, bolted to a set of flowmasters with no tail pipes.

What do you guys think?

 

[bobbyd]

Jrichker -

Jack the rear of the car up on jackstands and place the transmission in neutral. Make a paint mark on the rear part of the driveshaft that is visible from the side of the car. Make a mark on the tire, and rotate it one turn while counting the number of turns the driveshaft makes.

less than 3 turns of the driveshaft = 2.73:1
about 3 turns and a little more = 3.08:1
a little more than 3 1/2 turns = 3.55:1
almost 3 3/4 turns of the driveshaft = 3.73:1
a little more than 4 turns of the driveshaft = 4.10:1

See http://www.geocities.com/mgnedell/no...ch/speedo.html for information on speedo drive gears.

see http://www.corral.net/tech/gearcalc.html for a calculator that uses RPM, rear end ratio and tire size to calculate speed

follow that or this

TRWXXA -
The best way is to mark the driveshaft, turn the rear wheels 10 times, count the number times the driveshaft rotates, then divide that number by 10.

When you turn the wheels only once, it's hard to tell the difference between 3.08 turns of the driveshaft and 3.27 turns (or 3.55 turns and 3.73 turns, etc.). I know this for a fact. I thought I was getting a 3.08 rear end and really wound up with a 3.27 (even better). Only after I took off the differential cover and counted the pionion and ring gera teeth did I discover the error.

hope that helps

 

[dmontzsta]

Thanks for the link, it really helps. I estimated it with my car and it came out to 3.55, which is stock. We did his car and it looks like the previous owner has 4.10s in that bitch.

No wonder it is a freak.