After hunting through a q-jet grave yard, I've picked up a few rods and an extra pair of jets. The jets are 67's, the carb I'm currently rebuilding has a pair of 72's. Unfortunately I'm not certain if the carb is a 750cfm or 800cfm, if someone could give me a better idea how to figure out which is which i'll be very thankful. And yes I've checked out buickperformance.com but I still can't tell from the pic's. i have 2 pairs of primary rods and 1 one pair secondary, I'll post the numbers stamped on them later as I'm a good 20 klicks away from them right now. So here's the question, what's your recommendation for a currently bone stock 350 with auto, that will see headers and a cam with around 218 degrees @ .50" down the road? My goal is for a car that has great low end torque but is acceptable in the mid-upper rpm range, aka tire burner with economy. Am I dreaming to much on this one? Thx Swords
The difference between a 750, and 800 CFM Q-jet, is in the size of the last primary venturi. The venturi is formed by the carb body. On a 750 it's 1 3/32", on an 800 it's 1 7/32", and 1/8" difference. The larger venturi necessitates a bump in the venturi (to avoid uncovering an internal passageway) This picture may help.
All 800 CFM Q-jets are 455 carbs. The 455 needs more air than a 350 at idle, and low speed. Therefore an 800's idle system is calibrated differently. An 800 works really well on a hot 350 with a moderate cam. It may not work as well on a stock 350 even with headers. The 750 carb would be a better choice for a stock 350. Rule of thumb when jetting Q-jets, is for every 3 jet sizes you go up, you should increase the primary rod one size to keep your cruise mix the same.
