Still trying to get all of the bugs out of the new motor. I have a favorite uphill onramp near my house where I can really get on it. Discovered today that at 5500 rpm, the motor starts to backfire big time, but is fine when I shift to the next gear. I'm using a MSD 6AL with the YS trim blower (11# boost at 5700 rpm based on dyno pull). My mechanic said I didn't need the MSD 6BTM bacause I don't have a detonation problem (and this is definitely not detonation, I've had that with the old motor and know the sound well). I should point out that she seems to run fine on level ground, though I haven't had a chance to really test this carefully yet . So what's causing the top end backfire/sputter. Could this be related to the absence of a boost timing master? I don't want to damage my new motor before it even sees its first trip to the track.