Originally Posted by
Adam.Findlay
horsepower is horsepower regardless of gear as horsepower is just a measure of work done.
the gear only effects the measured torque. and the measured torque will only change if it is not referenced to crankshaft speed. referencing torque to crank speed means you will get the same the same torque reading regardless of gear ratio.
for example do a dyno run in fist gear and your torque figure will be off the charts high due to the large mechanical advantage of the gear ratio multiplying the torque, do it in 5th gear and the torque will be low due to the wheels being at a mechanical disadvantage due to the overdriven 0.8:1 ratio
but as said above the engine makes the same horsepower regardless of gear.
as you probably know horsepowe=torque/5252, so as you change up gears the torque at the wheels decreases due but the speed at the wheels also increases so the horsepower stays constant
most of the time dyno pulls are done in 4th gear as most cars have as close to all that matters a 1:1 4th gear ratio
that being said there is somewhat of a difference between rolling road and hub dynos as rolling roads have to deal with inertia of wheels and tyres as well as tyre size and pressures coming into play. and if the dyno is incorrectly calibrated for gear/diff/final drive ratios there will be variances.
probably a rubbish explaniation but I hope you follow