too small. you'll lose topend performance in the way of engine stutter and possible refusal to rev all the way to redline.

you'll get amazing low-end response tho... but after 4000rpm, you'll start choking the motor.

expect to lose 10-20hp

but it wont hurt your motor as long as you dont flog it. just be careful of detonation due to exhaust gas reversion from backpressure. i wouldnt rev her past 5000rpm if it were me.