Corvettelvr73

With a muncie wide 4 speed im turning 5500 rpms at 78 mph in 3rd gear and 255X60X15 tires. What gear do i have i cant figure it out becuase im not sure that my speedo is right that is why im using the dragstrip 1/8th mile timeslip.

72GACRZR

I can't tell you from that, but the codes for 1973 & 1974 in my reference book are:

AA=3.55:1 Posi
AB=3.70:1 posi
AC=4.11:1 posi
AW=3.08:1 posi
AX=3.36:1 posi
LR=3.36:1 posi

Hope it helps

BB wowbagger

What are the RPMs at 60Mph? :cheers:

corvettemaster

From my calculations I figured it to be 3.70

Clink69

Assuming you have a wide ratio unmodified in third you are at 1.46:1. Using that and 78 MPH @5500 RPM gives the closest of 3.90s.

Chris

Smokehouse69

:iagree: with Chris (Clink69)

Check out this link and plug in your numbers, you'll come up with 77.72 at 5500 rpm, using 255/60 15" tires, and 1.46-1 3rd gear ratio and a 3.90 rearend.
http://www.sgmotorsports.com/mph.htm

IETEK

This is suppose to workrun the car in 4th gear @ 75 mph and the tach should read the rear gear ratio e.g. 3700 rpm 3.70 rear gear I have a 77 and that is the gear I have ! :D

corvettemaster

Yep, you're right. I redone the math and it appears that 3.90's is closer than 3.70's.

My calculations:
(1000((5500*27)/((1.46*3.90)*336)))/1000 = 77.6 mph
(1000((5500*27)/((1.46*3.70)*336)))/1000 = 81 mph

the basic formula is: 1000((rpm*tire diameter)/((trans ratio * rear ratio)*336)))/1000 = mph


[Modified by corvettemaster, 4:50 PM 1/14/2003]