General Category > Quadrajet Carb Talk and Tips

secondary flap: what distance for full CFM ?

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Cliff Ruggles:
You pretty much have to tune on the dyno or at the track to find the perfect open angle for your particular set-up.

I've also heard that allowing the huge throttle plates to go over or under center helps on some set-ups as well, but I've never found any power there in all the testing I've done.....Cliff

garybohannon:
Some Buick guys say their stock and Edelbrock dual plane intakes run lean on #1 cyl. and a little over center helps feed fuel that direction. A 5 to 7 degree forward pitch probably hurts nothing since qjets dump more in back than front.
Some also Buick guys "stagger jet" the driver side primary up 1 or 2 jet sizes to help that #1 problem.
Never found any dyno or detailed documented proof.
However, on a single plane intake, distribution problems are solved with "turtles" or porting.

garybohannon:
My above comments referred to the Throttle Plates, not the air valve.
Air valves... A Pontiac guy said that an air valve gives "diminishing returns" if opened more than 80 degrees. Straight down or "fully open" is not recommended. May obstruct fuel nozzles and cause serious lean out at upper rpm's.
Cliffs 1.315" setting should be good enough. Stop there.

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