I am considering putting 3:73s in my '94 Z28, but I am having some doubts. Heres my dilema, this is my everyday car, so it has to get decent mileage and still be able to be driven on the highway. The car has an automatic, and I think 3:23s are in it now. Could anyone give me a rough idea what my RPM would be at 65mph? I have 245/40/ZR18s on the back also. I know now I'm close to 3000 at 65, and I'm just curious as to how much higher it will be. Thanks for any help.

 

Wha???
3.23s + A4 = ~2000 rpms @65
Even w/ 4.10s you should be at about 2600 at most...
Is there something I'm missing here?

 

Is this with your car in overdrive or just drive?

 

Yea, 3000 at 65 cant be right. If it is, im so glad i went with the m6 .

with 4.56s youd be doing 2700 at 65 mph.

 

I would say that your transmission has some serious slip issues if you are running 3000 rpms at 65. I have an A4 and 3.23 gears and when I am running 80 it is at 2600 rpms. If your trans isn't slipping than maybe you already had gears in it to begin with.

 

finally somebody beside me has seen the light, 4.56

 

4:10's and 3000 rpm. at 75 mph. hwy in overdive weekend car & nice day's, but what a great mod. woke her up alot!! 3:73 in a daily shuld be fine

 

maybe him having 18'' rims has something to do with it ?

 

The car must have gears in it already, I kind of suspected that. It shifts out of first at about 5 mph when cruising. The tranny feels strong to me, no slipping, it even chirps going into second. The car in overdrive is at 65 mph is definately over 2500, closer to 3 grand. Isn't there a way to see what gears are in it without taking the rear cover off, by counting the turns of the driveshaft compared to the turns of the tires? As far as the 18" tires, they are taller than the 16" tires by about an 1" so if anything they would drop the RPM on the highway. I never changed the speedometer because it seems to be dead on now with these tires going by radar.

 

Jack both rear wheels off the ground. Make one complete revolution with a rear tire and count the number of times the drive shaft spins.

If it spins just a little more thatn 4 times youve got 4.10's, a little less than 4 and its probably 3.73's. if it its a bit more than 3 times youve probbaly go the stock 3.23's.

 

Alright, thanks for the help. I'll probably do it this weekend, because now I'm really curious.