Engine RPM calculator

I went through the sticky and pretty much all of the engine RPM calculators are useless (dead links, happened over time, I think)

Looked at some old pictures of my 97. One of them was taken while on the highway. 72 MPH, 2100 RPM on tach, stock tire height, T45.

Thought about that for a second...my 04 gets about 1700 RPM same conditions.

Axle tag on the 97 did say 3.27's... but this got me thinking.

So-I used this one- http://www.crawlpedia.com/rpm_gear_calculator.htm

and it turns out that, most likely, it got a set of 3.73's at some point. That explains a lot about how the 97 felt vs the 04. Just found that interesting, thought I'd share.