STi intake pressure drop test
I tested my intake system today on my 2005 Sti (stock) for pressure drops. Results were:
Stock airbox & filter, stock resonator, removed ram duct: 42" H20 (1.51 psi) vaccum
K&N typhoon short ram, without the heatshield: 22" H20 (0.79 psi) vacuum
I placed the vacuum connection on the wastegate bleed/intake pipe nipple, without the bleed hose connected of course.
The WRX STi intake box is by far the most restrictive intake that I've seen tested to date. Mostly due to the fact that an STi flows 300 h.p. The K&N typhoon is really effective at reducing intake pressure drops: they've eliminated the flex bellows, removed one unnecessary tube bend, made the intake pipe only 8" long, included a huge intake velocity bell, etc. Filter size is on the small side, around 80-83 in sq.
Which makes more power? The stock intake box produces MUCH more part throttle and midrange power than the K&N. The K&N makes a touch more topend, but barely. I think the K&N is throwing off the Maf somehow. It feels like part throttle fuel is really lean. I'm sticking with the stock airbox because it produces more torque under the curve, even though its 2 times the restriction of the K&N.