going 60 MPH its at 1,500 RPM's. the tach is aftermarket and not the factory so i know it pretty close as far as acuracy goes. can anyone make a guess on what gear i have? its an 87 IROC 350 and automatic. id check the RPO codes if i had them...

thanx to who can help

 

You will need to know the diameter of your tire but then use this formula:
http://www.smokemup.com/auto_math/rear_end.php

 

Do you have disc brakes??? in the rear? A posi unit would be 3.27 borg warner, just a guess. But those numbers sound alot like my 86 LG4, and she had 2.73 one legger...... So it could be anything. Get back there and look at the tag on the rear end, should yield something!

Will

 

1500 rpm's & 60 MPH in OD would be 2:77 ratio which is a BW 9-bolt. Same as I have in my car.

 

its not a 9 bolt or a posi and it doesnt have disk brakes out back...yet

 

Well if you are sure that it is not a 9-bolt in back, my other guess would be its not a 350TPI in your IROC. Reason: 350's for 1987
came ONLY with a 3:27 9-bolt stock. Also they all had limited slip and disc brakes as required options.

 

sounds like a 277 or a 273!

 

I agree, its most likely the 2:73 with those supplied numbers. And since he stated it is not a 9-bolt rear that eliminates the 2:77.

So my guess is he bought a 305 IROC with the 2:73 10=bolt rear. Another case of it a 350 and you better buy it fast and did not check until now.