took their cars to Peco with me and then put it back on the rollers at Autogym a while later and they were both around 50bhp down on power.
I've had this arguement on the VXR Forums about dyno's.
If i took my car to TMS, Courtenay, Regal or DAP each dyno will be giving off different bhp values. this is down to a number of factors:
hymidity in the dyno room
air flow getting to the engine - fan types vary
what fuel you used (one day vpower the other bp ultimate)
there are alot of variables to take into concideration when taking your car on the dyno.