+1
When I had my old 350z dyno'd at Eurospec2000 a few years back mine heatsoaked massively. Monitoring on OBDII, intake temps on the way there were about 20C, obviously rising sharply when stationary but then going back down again within about 30 sec of moving again. When on the dyno the temps were well up there, somewhere around 30-40C IIRC So nothing like they were on the road. So I decided to leave mine on purely for the sound. I never got to put the standard box back on again before I sold it, so cant tell what the difference would have been, but I'm guessing it would only be from a standstill when a bit of heatsoak would have kicked in.