Will a ratio change affect dyno numbers?

[mitchntx]

If I dynoed 200 RWHP with 3.42s and immediately swapped in a 3.73 and redynoed, would I yield the same RWHP?

[Chris 96 WS6]

THe difference is negligible. Since a dyno samples RPM, there's automatic correction for gear ratio changes, but the difference is that numerically higher gears generate more friction. The difference won't be more than 5hp between the biggest gear changes, so 3.42 to 3.73 probably won't change your rwhp in any noticeable way.

[gettinthere]

Like Chris said, the gears won't eat up much, maybe a few at the most. You'll start to see a loss when going with 4.xx gears are a 9"/12 bolt rear.

[mitchntx]

The series I run in, Camaro/Mustang Challenge, we get dyno certified at the beginning of the season.

Based upon that cert, a minimum weight is assigned.

Occasionally, top finishers have their hood sealed and have to report to a dyno to verify their numbers.

So, if a racer runs extremely close to minimum weight, a 1% variance in the dyno number can mean the difference between a win or a DQ ...