one thing i notice about the secondaries is there is no venturi, I wonder if anything can be done with the delivery tubes to promote better atomization, and if the BBB would respond well to it.
The Q-jet was used for over 20 years and is a pretty highly engineered carburetor. My guess is boosters were not needed to accomplish more uniform distribution. At least any that would be picked up in BSFC's numbers versus HP. The Thermo-Quad doesn't have them either.
The secondaries are for high load/full power. Venturis would cut down on the maximum CFM I would think.
You can burr up the air door and throat on the secondaries, file grooves on the door edges or even bend small tabs in the doors to promote tumble but I wouldn't expect any gains , the Qjet is hard to improve upon
Right on the dyno my 1977 Pontiac q-jet outran a very well prepared Holley 4781-2 850 double pumper carburetor with down leg boosters in it. The BSFC wasn't quite as good for the q-jet, but it still made MORE power. We did this as part of the magazine articles for HPP and Popular Hot Rodding a few years back. A private track rental followed the dyno testing, and at the track the q-jet outran the big Holley carb by .02 seconds and .30MPH, almost exactly the difference in power shown by the engine dyno runs a few days earlier. No real reason to modify the q-jets big secondaries in any way to improve atomization, they do a fine job and work as good as any other carburetor at the track once you get them dialed in correctly......Cliff http://www.highperformancepontiac.com/tech/0501pon_kre_aluminum_heads_dyno_results/ http://www.highperformancepontiac.com/tech/0502pon_kre_aluminum_heads_track_results/
So i take it we dont want to induce swirl at the bottom of the carburator. Ha. I was thinking of and still may try soldering a coarse screen at the exit of the tube just to satisfy my curiosity. Cliff, was that a single plane intake on your Ventura? Have you compared perf of q jet on single plane to dual plane intakes?
I've tested every intake that will fit under the hood, and every type of spacer as well. Here is a link to a thread that I ran recently on intake testing. http://forums.performanceyears.com/forums/showthread.php?t=757739 All single plane intakes that I've tested required at least a 1" spacer on them or they were way down on power compared to no spacer at all. Even at the power level of my engine the stock intake feeds it equally as well as any of the other intakes that I've tested to date. What I see with aftermarket intakes is typically a shift in power, so the car slows down in 60' times but runs a little faster on top end, usually a little less in ET.....Cliff
Your talking Pontiac though arent you. I seriously doubt the stock Buick iron intake is a real runner or even close to the eldlebrok B4B, The Poncho iron intake with the angle carb pad, air gap underneath, dual plane is a fine intake. I may have to rethink my build before I make any more purches, I was planing on TA TE heads, intake raised runner advantage, with an sp2 intake that totals 4 inches taller , add a 1 in spacer and my hood will look ridiculous. If I go with the TA SE heads and the sp1 intake , I in spacer , im still looking at 2 inches in needed hood clearance. But if I go with the B4B dual plane, TA SE heads, 1 in spacer Im only 1 inch in needed clearance, The only sacrifice will be about 15 horsepower at the top end. My goal is a 12 and under sec 68 Riviera with 3.08 rear gear, one legger. 1/4 mile car. Is that possible with a 3.08 rear? How much porting have you done on an edlebrok b4b. I had the b4b on my last motor and I cut an inch out of the divider, blended in the first turn a little, and matched the carb pad to a thick open Q jet gasket. I used a long piece of emrycloth sand paper and pulled it back in forth to smothen the last turn a little bit.
