About an extra 100 CFM over the 3" MAF. Technically even a stock 3" with the screen in place will flow enough to provide 900 hp. The real limitation is how the ECU interprets the signal. In most cases, the ECU will peg the air flow at the max long before the MAF's max flow rate has been achieved because it can't calculate anything beyond an upper limit. There's plenty of modified engines that hit the MAF signal limit by 4000rpm, at which point the ECU switches to a fixed fueling table, which is typically a bit on the lean side. Custom tunes often redefine some engine parameters to make the max value relatively higher at the expense of fine precision. Custom ECUs can have maps that allow the entire range of airflow to be measured accurately, though that's rarely beneficial at WOT anyways.I'm using an F-Body MAF. Larger than the B-Body MAF but I do not know the difference in CFM other than it is more.