Dirt track vent..

a 500 CFM 2bbl pulls 628cfm at 7 inches vacuum, not a problem on a circle track motor. "...A 650 carb on a 358 cubic inch engine will seldom see 1.5 inches but a 350 (500) carb on the same engine will frequently see 5 to 8 inches. At 7 inches of vacuum the 350 (500)carb is really flowing about 430-440 (628) cfm..."Holley 2 Barrel Carburetors & Holley Double Carbs | Camcraft Cams

Mallory ran a series that only used Mallory ignition. Said it limited the top end to keep the build cheap. IIRC hard rev limit at 7000 or something. that makes a little sense as someone could not run a 9500 NASCAR motor to its potential. Its all money. you run an unlimited class and you will lose if you are not uber rich, or are not sponsored by a deep wallet. Who would want to see the same car win every race its in, outclassing every other car in the race? Think the first year Hemi in NASCAR or even the Hyper pak slant in the 1960 NASCAR jr. series. Remember that snooze fest IROC? talk about identical cars, they were just painted differently, almost like "the car of tomorrow" in todays NASCAR. Same chassis, choice of 3 motor builders or some crap.