When i first built the 5 i didnt bother with an air filter/ pipe.
So it was sucking in hot air from around the turbo.

Then i put 2 90 hoses off the front of the turbo it turned right then down and put a big filter on it and a hose from under the car to give it some nice cold air.
It made quite a bit of difference and more responsive.



Also a mate has a very high power subaru legacy with new impreza engine/running gear. (600 odd bhp)
At one stage on the rollers he gained 70bhp by just opening his bonnet! His air filter was being starved of air and it was hot, as soon as it got lots of cooler air it jumped 70bhp without touching anything lol.



All it will cost you is a couple of hoses off ebay, try it!