Originally Posted by vinniekq2
If you have 5.? gears you should know?When I had 5.13s I was at 3700 rpm on the hiway. At 7,000 rpm I was a little over 100MPH.top speed was 115. with 5.? gears you will feel all the shifts and certainly feel slippage
X2 on everybody's advice, I had 4.88 in my 67 Firebird and at 60 MPH the RPM's where around 3,500. Top speed a wopping 107 MPH and that's what it hit going throw the traps at the end of the quarter mile.....once, I will not speak about the other times....LOL.
Count the teeth in your ring and pinion...do the math that way, then you know for sure. If your not sure about the transmission, try shifting it manually...see if your RPM's drop from 1st, to 2nd, to drive. If the RPM's don't drop from 2nd to drive, you don't have a 5.21 rear dif.