I had made the decision to swap the smaller carb after reading a few carb comparison articles. On a small Chevy, there was a comparo done between a slew of Holleys from 390 up to 950, all mechanical secondaries. The difference in peak and average power from the 650 to 750 was so slight, probably 4-7 hp IIRC, but the response was so much better with the little guy. I have not put my car on the dyno to personally prove it, but my *** dyno tells me that the smaller carb is a better choice. Pulls like a bull to 6500 and that's all I need.
