I'm running two of them on my 427. There EXPENSIVE drag race carbs. No power valve and the "secondaries" are VERY close in size to the primaries. The secondaries are slightly bigger, but it's hard to tell "looking" at them.
The mechanical linkage is VERY FAST. Center Squirters all right. The accel pump shoots into all four barrels at the same time. Thus the linkage is set up to open the secondaries when the primaries have just barely opened a little. Everything about these carbs is "fast". BIG accel squirt IS needed to avoid stall. Linkage travel distance is kind of far, keep pushing down eventually the pedal will hit the floor board and the carbs will be wide open.
I hate them! I've done ALL the tricks to make them more street friendly, it's just not in their nature. They flood REALLY easy on even modest cornering or modest braking. The go in straight line really really good however. They LOVE to run wide open throttle. Two 660's are 1320 cfm. Normally I would say that's "too much". But for MY motor setup it's "perfect"! I run high 11's at 120 plus in the 1/4, and thats taking it "easy" on the car. I DID re-jwt from 75 to 68's (total of 8 jets, all same size) and that actually HELPED performance.
If they didn't LOOK so cool and RUN so fast on the drag strip I'd sell 'em and go with something else. But there so bad, there good! I'll keep 'em, love/hate relationship.
OH, I forgot to mention the "idle circuit",,,,,, wait, they don't have one thats worth mentioning.