The on3 turbo has alot of back pressure . Made 940 wheel on 25 psi . On 20 psi it took alot of dome pressure so we added a back pressure sensor . And its about 1.5:1 back pressure to boost . Also my engine seems pretty weak , so i need to do a leak down. Still super happy with the kit and everything ! Picked up my forged 370ci shortblock from the machine shop this weekend so tham be going in soon .