Reply to "Dyno run gone bad"

Originally posted by JFB #05177:
why would one be going through the gears during a dyno run?

To read correctly, a chassis dyno must be at 1:1 input to output through the tranny. A ZF trnsaxle does not HAVE a 1:1 relationship between input & output. The operator may have been searching around for the closest approximation- which in a ZF is 3rd gear at 1.04:1.

Running at other than 1:1 gives different power readings. I once asked the Mallory dyno operator to verify this on Judy's Z-28, using 3rd and then 4th gear (auto tranny) only a minute apart. Sure enough, all the horsepower numbers were different in the two gears. In newer dynos, there may be a software factor to tune this effect out, but there's a LOT of older dynos around....

Of course, using any dyno as it is meant to be used- as a comparative tool in tuning- the actual numbers don't matter. What's important is the % varience from one run to another while changing something in the engine.