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)
air temp
etc
there are alot of variables to take into concideration when taking your car on the dyno.