My vote would be a vacuum secondary carb, specifically the Edelbrock AVS2 series. Much easier to tune for me than a Holley and they work great on the street.
Kudos to you. That is exactly what I would ask. Despite not being from Missouri, I'm a show me guy too.
Data, maybe some somewhere. But at some point you need to choose what you want to believe based on the source. I'm fascinated by how there can be a ground swell of miss information that cannot be unravelled.
Generally I don't talk about the road I've traveled in my hot rodding history to get where I'm at today. I'll just hit a few highlights.
Almost all my experience is on street cars. Probably over 1000 track passes with my own stuff, and that pales in comparison to all the street racing I did. Along with that, there was a core group of us, usually 4 or 5 other guys that were doing the the same thing, kinda of a competition to out do each other on a week to week basis. I would change camshafts on Saturday mornings. We tried and traded carburetors all the time. All the: is a Holley better or a Carter, is big better than small, is vacuum better than DP was tested and concluded 40 years ago. But even so, today I've still got about 12 carburetors sitting around here, including a 3310-1 as you know is actually a 780 with the down leg secondary booster and rear metering body.
The stuff I post always comes from real personal experience, or observation paired with experience.
At the risk of sounding arrogant, when I go to the track, most folks that come by are very surprised what my cars run considering what they are.
Take it for what it's worth.
My vote would be a vacuum secondary carb, specifically the Edelbrock AVS2 series. Much easier to tune for me than a Holley and they work great on the street.
But the AVS is not a vacuum secondary carb. Ron
Gentlemen,Sure it is.
Adjustable Vacuum Secondary (AVS)
The secondary plates are mechanical but they are operated off of engine demand (vacuum) not throttle position.
Gentlemen,
AVS stands for Air Valve Secondary....this is Carter's terminology. The adjustable secondary air valve responds to AIR FLOW thru the secondary butterfly / fuel admission nozzles. This is IDENTICAL to Holley's vacuum operated secondaries, which operate in response to the air flow thru the PRIMARY venturii by measuring the pressure drop thru the venturi. This response is adjustable via the SPRING TENSION on the secondary operating diaphragm, which equates to adjusting the tension on the secondary Air Valve's operating spring. Are both carbs on demand types.....YES. The methodology of achieving the end result is slightly different but the end result is the same.... an adjustable secondary system.
This is just my opinion.
Bob Renton
Ron,That's correct but the AVS is not considered a vacuum operated carb since the throttle plates open mechanically. And AVS stands for Air valve Secondary. Only the air valve above the throttle plates open by eng demand by the low pressure under the air valve and the atmospheric pressure above the air valve. Pretty much all mechanical secondary four barrel carbs use some type of an air valve to control eng bog and stumble when you floor it. The AFB's use a weighted air valve in them. The Quadrajet uses a secondary air valve just like the Thermoquad does that its opening is controlled by spring tension and the choke pull-off diaphragm. The Ford Autolite carb uses an air valve that is controlled by spring tension and a damper piston in the fuel chamber. And even the old Rochester 4GC carb is a mechanical secondary carb that uses an air valve.The only carbs that I can think of that are considered vacuum operated secondary four barrel's are the Holley's and the old Autolite carb used in the 60's that also used a vacuum pod to open the secondaries. A vacuum secondary carb means the secondary throttle plates are opened by a vacuum pod. All the carbs that I mentioned that use an air valve are considered mechanical operated secondaries because the throttle plates are opened mechanically and not by a vacuum pod. Only the Holleys and the old Autolite carb that use the vacuum pod to open the secondary throttle plates are considered as vacuum opperated secondary carbs. Ron
Ron,
I think the METHODOLOGY of introducing additional air flow/fuel flow is a matter of semantics. Yes, Holley and the old Ford /Motorcraft 4100 series measured primary venturii pressure to achieve the secondary opening method; once the air flow begins, the fuel feeding systems begin to function. The AVS, Q-JET, THERMOQUAD, MOTORCRAFT 4300, etal, operate as you described BUT the important criteria is the fuel is added to the air stream as the demand for it increases as determined by the engine air flow. In short, it can be said: "the difference is the same"....seamless operation.
Bob Renton
I agree the method is different, results essentially the same. Still very different than the true mechanical secondary style.
Actually about the only mechanical secondary carb I can think of that don't use an air valve is the Holley double pumper carbs. And of course they have to use a secondary accel pump to eliminate any bog. Which of course is what the air valve is for on any mech secondary carb that don't have a secondary accel pump. Pretty much all mechanical secondary carbs use either an accel pump or an air valve in the secondary side to stop any bog/hesitation. Ron
Actually, certain models of Q-Jet carbs, I believe Chevy and Pontiac applications , use a POE (Pull Over Enrichment) feature with calibrated orifices in the air horn, directly above the secondary air valve, which, when exposed to vacuum, just as the air valve blade starts to open, begin to feed fuel (similar to an accelerator pump's operation) to eliminate any momentary lean condition, until the main nozzles begin feeding fuel. Perhaps the "best" of both designs....double pump vs AVS designs. Just my opinion of course.
Bob Renton
The Carters lift the rods too.
Ron, OK, guess I mis-read your post. My aftermarket AFB has rods on the PRIMARY only. Sorry for the confusion. I'm still a Holley guy, for better or worse.