they do restrict pretty much but it dont take all that much power from the motor and you wont notice it cause the restriction goes up with boost so the more restiction you have the more power its making at that point so you cant tell


like on turbo buicks the factory tuurbo is small so you dont get lag but in return it gets 2# of backpressure for every # of boost

that ratio of exaust pressure to intake pressure causes it to spin the turbo up faster

as you get into higher output turbo's (bigger) the wheels are matched to give a better ratio of pressure from intake to exaust..

like say the wheels are set up at 1.5# back pressure to each # of boost... at that point you make more power at the same boost level only because you have less back pressure but in return less pressure on the exaust side causes it to spin up slower (lag)

once you get up into big race turbo's you can get down in the 1 to 1 ratio on back pressure to boost but thats where you get into high rpms before you get enough exaust to spin it fast enough to start making boost

hope somebody can understand that ...LOL