Desk Top Dyno

You don't have to buy it. There's a free version online you can download. Search Desktop Dyno 2000 and you'll find it. IMO that's about the best incarnation because it's still simple. Some of the later versions get down right complicated and take the fun out of it.
Ah thank man that was awesome. I did t know that or even think about that. Complex (to be accurate) is good but not fun. The bad the first or near the first version where the dyno graph lines would quickly move across the screen revealing the estimated power curve. That was cool.