Hey, i wanna know what speed gear I am supposed to use to have a correct reading on my speedo. I have an 83 Z with a 350 and a TH350 tranny. The rear end is 3.23 and the tires are 205 in the front and 225 in the back. Soon to be 235 all the way around. On 16'' iroc rims. How do I figure this out and where do I get the correct speed gear from? Where do I take out the OLD speed gear and put the new one in, what part of the tranny?

You'll need to know the height of the tire, not just the width. Gears are available from the dealer and there's a tech article that tells you how to do it.

By the way, try <a href=http://members.shaw.ca/crussel/speedo.exe>this</a>.

Either TCI auto is way off or that program is way off.

TCI says I would need for my application:

7 drive 18 driven
8 drive 20 drive


That program says I would need

7 drive 19 driven
8 drive 21 driven


Hanlonmotorsports says

7 drive 18 driven

One of those is going to be pretty off......

Just an FYI for whoever stumbles on this thread in a search