I'm working in 4wd, with a modern turbo charged car.  You can't use the traditional run down method to measure inertia as the ECU will reduce load when it detects engine speed decreasing under full load.

I was getting a little below stock quoted flywheel figures when run in 4th gear.  Running in 5th gear, i was showing over 30 bhp more.

This is with an inertia of 3.9 per axle on a DynoDynamics setup.

I adjusted the inertia until I got the power to line up fairly well, doing a power run in 4th and 5th gave very similar figures, which ended up at 3.1 per axle.  The issue is, i now have to set the correction factor to 19%  in order to get a sensible stock figure.  I know this car and what it normally puts out stock on different dyno's and it's always 300-310bhp.  With my corrected inertia i'm only at around 257bhp.

Thoughts?

Dev.