[Cliff R]

"the early Pontiac SD455 and Buick 455 1970-74 carbs were always listed as 800cfm rating"

The 71-74 Buick 455, 73-74 Pontiac Super Duty carbs are the only large castings made before 1975.

All front inlet 1975-up automobile carbs will also be the larger castings.

Some side-inlet Chevy units were stil the smaller castings thru 1980.

All of them would flow 850cfm if the stop were ground a bit to mimic the open angle as used on the Edelbrock 850 cfm Q-jets.

The 1971 Pontiac carburetos missing the outer booster rings flow 827cfm.

Over the years folks just got in a habit of calling any large primary bore q-jet with a "bump" in the castings "800 cfm". Most were less than 800 cfm as the stop for the air doors limited the full open angle some.

As far as making power once you dial in any carburetor for the application and it flows adequate CFM nothing else is going to outrun it. I've proved this over and over again on the dyno and at the track back to back testing. IF you are using a dual plane intake designed for a spread bore carburetor it actually has an advantage over a square flange carburetor on the same intake as the plenum areas are wider, the intake has more volume, and the carburetor bores are lined up right in the center of the plenum areas.

This is how I continued to outrun every other type of carb tested against my 1977 Pontiac Q-jet for so many years. We ALWAYS made more power on a dual plane intake than anything else bolted on right after it for the next run.

My Q-jet didn't fair so well on single plane intakes and power was typically WAY down unless we used at least a 1" spacer to get the huge secondary throttle plates up and out of the plenum area.

As far as running w/o a primary power piston and metering rods it works quite well and eliminates any moving parts plus more precise fuel flow thru a single hole vs a hole with a metering rod hanging in it........