What gear ratio in diffs does it take to make the drive train take higher power levels? Will 4.88 or 5.13 be low enough or do you need to get into the 6.20 range? Just thinking about some changes for next season.

I know guys out there doing it with 4.10's, but numerically higher is better. If you can get to 5.13 or higher then you are better off IMHO.

AP

I am still running the 4.10's but like Alan said, get it to the 5.13 mark and you will have a lot less problems. I found that once you get u-joints to stay in place that you start to twist the splines on the driveshaft slip yokes!

Has anyone put 5.13 in a d61 front? I had 4.88 with a spacer the pinion has 8 teeth and so does a 5.13

What kind of power would it take to run a 25 final on mostly hard clay type tracks, with dot tires?

Depends on what size tire but with a 35" tire I can turn a 26 final with around 680 horse. This is real horsepower not the over estimated, inflated numbers that everyone normally quotes! So I would say in the 700 range or a little more would be ok.

If you are going to run a Pro-Fab three speed just keep putting in a higher headset until you can't get it to spin out and then go back down one from there. Every motor is different. Good Luck!

Depends on how much power you get to the ground

James you should qualify your statement a little. It doesn't do a person much good if they can pull a 25 final but only turn 5000rpm doing it.

Alan, very true. Mine turns around 7000 rpm. Not a high revving motor. A lot of it depends on where the motor makes power.