Took closer note of throttle position on todays flight. At 2000 ft the throttle was only about 1/3 open (position of throttle quadrant, but it closely mirrors butterfly position) at economy cruise setting which was 6.0 GPH. This is about 42% power, 82 HP according to the EM2 which is fairly close but not perfectly calibrated yet. The same power setting with the -B drive would bave been a bit further open.
I did a quick check of MAP at 1000 ft at full throttle and found I was not getting any drop at 150 MPH and had .5" boost at 220 MPH (ram air recovery I assume). I did not get around to checking it in slow climb which would more accurately compare to what you would see on a dyno.
Finally got some reasonably calm air to do performance comparisons of -C drive vs -B drive. Without the prop blade cuffs it looks like the break even point is at 203 MPH. Above that -C burned more fuel than the -B. After installation of the cuffs, the break even point was off the scale! i.e., above top speed with -B drive. I had a good data point on the -B drive while burning 17 GPH (209 mph during SUN 100 race). At the same speed, the C drive was burning 15.8 gph. This was better than I had hoped for.
Tracy

    Thanks, Tracy. I was hoping there would be someone out there
    flying with the same TB diameters.

    Like most things, TB diameter is a tradeoff. My conclusion from
    the dyno data is that 44mm per rotor (1 ¾) is a bit small as the
    MAP is dropping off over 5000 RPM. But if you want to idle at
    1500, and have a decent transition from there to 3000; 1 ¾ is
    good. For a 2.85 to redrive, I’d want to increase that flow area
    by 30% or so – to about 2” dia for each rotor.

    My data may not be representative because of restricted flow to
    the TB. The ‘airbox’ size is restricted by the cowl, and may have
    restricted the flow a bit. In hindsight, it would have been smart
    (and easy) to make a run with the airbox off and see what
    difference it made.

    Al