We based our opinion on the "feel" of the car. Mike, like me, is very intune with the way the car is feeling, so just like when you put on a free'er flowing exhaust, there is a noticable increase in 'pull'. Not a huge amount extra, but noticable. Not very scientific I know.
There is more chance for air to flow in to the intake, the stock air box on a GTV6 has a very small inlet, much smaller than the AFM. I have seen some spirited discussions here on the BB about 'cone filters' versus stock as to performance increase.
I think when you are moving that area of the engine compartment gets a certain amount of fresh air flow naturally, as the warm air around the engine is pushed back, down and out. I think modding a larger opening to behind the grill would help keep air intake temps down.
Is there a large difference in performance determined by the warm/cold air induction?
All that said, I like the kit, it sounds better and looks cooler too!
The " Save the Rusty Alfa Society"
43 Alfas at the moment [ I think], I'll be able to tell better when the snow melts