Terry,
I know some of this might be an "apples to oranges" comparision but here's something we found that might help you out next season. I've always set the "total timing" advance at 32-34 BTDC and on our VW motor it likes it to come in early (all in by 2000 RPM, a drag motor). This last year we started playing with NOS as our power adder. At that time we installed an MSD retard box on to our exsisting 6AL system. We use a 3 to 4 degree retard chip when the NOS is engaged. And we have backed down the total timing to 30 degrees max.

What we found is the reduction in timing advance produced very little loss in low end power (our 60 ft times did not change since we leave at 6700), but a big jump in top end MPH even on runs without using the N.O.S.

How much total timing are you running, at how much boost? Do you have a way to retard the timing as the boost increases? I'm not "blower savy" guy but I do know that you can't run much static compression compared to a normally asperated motor.

Just wondering if this might be connected to you blown head gasket problem?