I posted the following on a previous thread, dealing with my experiences with both carb models. The CFM numbers were for a stock displacement 428, as I recall:
"FWIW, my experience with the Holley 1850s was less than optimal. I fiddled around with them for several years and was never really satisfied with how they ran. I could get them to run at low speed or at high speed but not together. I went with the 6224s, swapped the metering blocks from the 1850s (which have the power valves) in place of the ones which came with the 6224s (which have the power valve holes blocked) and played with the jets until I was satisfied. I ended up with #72 jets in the primaries and secondary plates equivalent to #76 jets in the secondaries. I hooked up a vacuum gauge directly to a port in the manifold, duct taped the gauge to the dashboard and recorded the manifold vacuum in each gear at 1000 rpm intervals; lowest vacuum was at idle at 10.5 inches. Based on that I installed 8.5 power valves. Seems to have worked out OK but was certainly a frustrating and expensive way to go.
To expand a little on what Mr. Scobra said, if you run the numbers from Holley, you could get a dual-quad setup using the 450-cfm mechanical secondary Holleys (model 0-9776) and have plenty of carburation for your engine:
http://www.holley.com/HiOctn/ProdLi.../FMSC/FMSC.html
Inputing the numbers in their formula, you need about 805 cfm if you run your motor to 6500 rpm and assume 100% volumetric efficiency. The 450 cfms are considerably cheaper than the 660-cfm 6224s, $175 each versus $455 each for the 6224s.
Incidently, if you get to fiddling around with the power valves, be aware that just because the package says "8.5" doesn't mean the valve opens there. I have one of those little power valve testers and a hand pump and took it to Loper's with me when I bought the two valves in the car. We went through about a dozen before I found two that actually opened at 8.5 inches. Range of actual opening vacuum readings was from 6 to 12 inches. The guys behind the counter were a bit miffed that I did it until they saw the variations for themselves.
Also, if you elect to go with a dual 1850 setup, be aware that you will have to get the little caps for the secondary dashpots which have the nipples which allow you to hook the two secondary dashpots together, to ensure that they open at the same time. Holley wants about $65 apiece for them. One of the guys I work with rebuilds old BMWs for a hobby, and we took the dashpot covers which came with the carbs, drilled horizontal holes; inserted small-diameter stainless steel tubes and epoxied the tubes to the covers with some really good industrial-strength epoxy. It solved the opening-together problem but the I couldn't solve the not-opening-all-the-way problem. That's when I finally went back to the mechanical secondaries on the 6224s. Hope this rambling is of some use to you."
In final summary, I'd have to say that I agree with the assessment that the 6224's are drag racing carbs and as such are not optimal for the street. However, I never could get the vacuum secondaries to open properly, so I've come up with some "yankee ingenuity" to modify these to work. My biggest problem now, as listed by others on this thread, is some bogging down during rapid decelerations and a slightly smaller bog when going around corners hard. But, when I say GO, it goes. Like everything in life, it's a compromise.