What Is Your Mph At The Top Of 2nd Gear?

[Jace78]

Hoping for someone with a stock rear end (which I think I have) to compare against but any will do, I may be able to calculate....my other thread says tach fixed and high rpm problems, paid close attention on the way home and now doubting myself.

I pulled 72mph @4500 in 2nd gear...

Normal? rpms seem too low? what do you pull (please include rear end gear ratio)

Thanks!!

 

[RangerJoe]

1.94 second gear ratio, with a 3.73 rear end and a 25.7" tire, I get somewhere around 60 mph.

http://www.wallaceracing.com/Calculators.htm

There are a lot of good calculators in the link above. You can figure your tire height, then use that with your rpm and mph to figure rear gear ratio. Assuming your tach is correct and not malfunctioning, I think you would have a pretty high gear in there (2.73 maybe?).

Joe

 

[Jace78]

Well, using the calculator I should be at 5100 but...should it not pull past 5100? tach seems a tad off but not as bad as I thought.

 

[jrichker]

This chart is based upon stock 225-60- 15 tire size

 

[Bullitt95]

I pulled 72mph @4500 in 2nd gear...

Your tach reads way too low. Stock 225/60R15 tires turn at 815 revolutions per mile so with stock 3.08 axle gears, the engine will turn at 2510rpm at 60mph in 4th gear. Therefore at 72mph in 2nd gear, the engine will turn at ~6000rpm.

 

[Jace78]

So stock tire height 25.63, mine is 25.68..so very close. My thoughts may be correct then... even if I am at 2.73 rpms seem low... I guess I am going to go with chalk method, unless does anyone know if I can tell what was installed by the VIN?

<<edit well, 65 mph at 2000 in 4th, 2.73 i guess >>

 

[gearheadboy]

All this to find the factory axle ratio? Look at the door tag, axle tag, or spin the yoke and count the turns till the tire make a complete revolution. Lots of calculators out there as well.

 

[88LX5.Oh]

Or take the cover off the differential and look for the ratio?
Rear end probably needs to be serviced, anyways.

 

[Jace78]

All this to find the factory axle ratio? Look at the door tag, axle tag, or spin the yoke and count the turns till the tire make a complete revolution. Lots of calculators out there as well.

Ya, currently working 12 hour days with 1 day off a week for the month of October, lol just was trying to figure it out at work. Looked all over the cars and did use some calcs, was looking for confirmation is all Driving the car back and forth 1 hour to and from so plenty of time to mess around in the car but when I get home I just usually die so no time to think about or do anything Just get my ducks in a row to knock a few things out on my day off

 

[ratio411]

Doesn't the rear end have a tag under one of the cover bolts?
That will have your gear ratio right on it.
They are hard to see some times...

 

[TOOLOW91]

there's a letter on the door tag indicating ratio ... there's a chart some where to cross ref

 

[88LX5.Oh]

Well the tag on the dif is easy.
First 4 characters are the rear end gear ratio and if it's a traction-lok set up.
For instance lets say you have 3.08's and limited slip. It would read 3L08, IIRC.

 

[tca7291]

Look at your door tag, there will be a little box labeled AX, that is your axle ratio.
1991 mustang svc. manual designates:
open lock ratio
8 M 2.73
Y Z 3.08
F R 3.45
5 E 3.27
6 W 3.73
2 K 3.55

 

[Jace78]

Alright then, 2.73...thanks, time for gears and rear end service!!

 

[tca7291]

Glad to help!!

 

[stykthyn]

with 315/35/17 tires I pull a hair over 60 at the top of 2nd.