NineMeister

From seeing a photo of their cell in operation courtesy of Adrian, I can confirm that Sportec use a 4wd version of the Bosch FLA203 2wd dyno that I also have, not a Maha. In standard form this dyno can run in loaded mode (fixed tyre speed) for steady state mapping and in inertia mode for typical power tests across the rpm range. I have recently upgraded my FLA with a Dynostar control system & software package, the key advantage to this upgrade is that I can run in inertia mode with additional eddy current braking, thus simulating a bigger roller which comes in very handy to slow down the acceleration of large hp turbo cars and load them up correctly whilst making a power pull.

I agree with Geoffrey that the only real way to run aircooled engines on a chassis dyno is to remove the hot air from directly under the engine. I used the same Bosch dyno at another shop which only had conventional mobile fans and I had a lot of problems getting consistent results. Interestingly the best we achieved is when we used the fans at the side of the car blowing hot air/exhaust fumes away from the back of the car, i.e. not with a fan blowing at the engine.
In our own installation we dug out a trench in the floor under the dyno and fitted a large in-line axial fan to extracting the hot air from under the engine through a grille at floor level. The difference in the consistency of the results is astonishing - in combination with a down fan to blow air onto the engine lid we can now run 600+hp turbo engines without suffering heat soak in the intercooler and can do three consecutive runs on the same car and get measurements within 1hp of each other.