2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
A few interesting calculations for the performance seekers. An 850 cfm Rochester QuadraJet has primary bores of 1.375" and secondary bores of 2.25", for a total of 10.88 square inches of "hole" area. Your desired N* 80mm throttlebody comes out to just over 8 square inches of "hole" area. About 27% less than the monster QJ. BUT, the QJ supports engines from 400 c.i.+ to over 600c.i., while the N* throttlebody supports a 280c.i. unit. (This is exclusive of butterflies and shafts) One of the most common complaints of the carburetor performance crowd, after installing some huge carb (bigger is better) is a pronounced flat spot off-idle and a sluggish midrange. (Sound familiar?) Why? Too much airflow exactly where it's not needed --- low to mid-rpm. If you want to win in the stoplight GrandPrix, try a smaller throttlebody for higher air velocity at the port. Remember the Venturi principle: as area decreases, velocity and pressure increase. As the venturi widens, flow and pressure decrease rapidly, actually creating a vacuum downstream of the butterflies, which is one of the reasons a carburetor "works". Think about it.......