installed 3.73's have ?'s
 

I just had 3.73's installed in my 98 Z28 A4 and I was just wondering were my RPM's should be at like at 60, 70, and 80. Because when I'm driving on the interestate or something at 60 my RPM's are at 2300, 70 they are at around 2600 and at 80 they are around 3,000. I just wanted to make sure this was normal. I also tuned it with the Hypertech Power Programmer if that matters. Thanks for the help in advance.

Re: installed 3.73's have ?'s
 

Sounds about right. I turn 2500 @ 65 or so. I used 25.75 for the tire height.

Re: installed 3.73's have ?'s
 

Both of y'all are off. You should be reading right at 2,450 RPM's at 70 MPH in 4th. You won't get Hypertech to admit to the problem, but their tire height adjustment for the '98 cars is backwards. I don't know if it's backwards for the '99's as well or not. I had the same problem when I had my '98 T/A. Just ask those with '98 cars about my "fuzzy math" calculation for gear adjustments. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> Also, you're not supposed to use the advertised height of the tire that you're running. It will compress some from the weight of the car. You're supposed to mark the tire and ground, move the vehicle forward until the tire has made one full rotation, and then measure the distance (in inches) that it rolled. Divide by pi (3.1417), and you'll get the tire height that you're supposed to program in.

Trevor

Re: installed 3.73's have ?'s
 

That's some good information for EVERYONE, from a person definitely "in the know". Thanks Trevor. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> WJ.