Cliff,
It would be great if those Qjets flowed 850 cfm, but they've been called 800 cfm by some very reputable sources for a very long time- such as Doug Roe, back in the day when they were still being put on cars new, i.e. 1973.
If we're going to now second guess these sources, then we can second guess all the carburetors made out there, and add 50 cfm at will. You know as well as I do, the people who started using the 850cfm number, were Edelbrock, when they copied a truck carburetor exactly. Opening the air valve or throttle a hair more, doesn't add 50 cfm. I'd have to see it on a flow bench at 20" to believe it.
I remember specifically seeing from several sources, information stating the throttles should NOT be opened into a vertical position, they should be in line with the baffle- and it was designed that way for a very good reason- not to open all the way.
If you have enough motor and rpm, yes indeed it could flow 850 cfm. But that's not what it would flow at 1.5" HG, or 20" water, the traditional testing standard. The guy at Stealth Carburetors explained it this way, when I asked him what their carbs flowed:
"it is dependant on the engine
a 1.250 venturi carb (650) on a 350 engine at 4000 rpm flows 400cfm
a 1.250 venturi carb (650) on a 430 engine at 8000 rpm flows 880 cfm
the actual "flow" is dictated by engine size and rpm not carburetor size
the true CFM is not determined by the carburetor ---it is determined by the engine, but in the retail world this is how people determine CFM with a carburetor:
1.6875 throttle blade--1.250 venturi =650
1.6875 throttle blade---1.300 venturi=700
1.6875 throttle blade--1.345 venturi = 725
1.6875 throttle blade--1.375 venturi =750"
so...can you add 50 cfm to a Qjet ? sure, if you have a monster motor, and rev the piss out of it, until it pulls that much through the venturis by sheer force.
but the standard of the industry still is 1.5" HG/20" water. not what the biggest engine made can pull through it.
|