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High Flow Holley 4412 2 barrel Carbs

Posted: Fri Mar 17, 2017 3:02 pm
by NormS
I've been working some Holley 4412 500CFM(@3"Hg) 2 barrel carbs to see how much air flow I can get through one without detracting from its ability to meter fuel efficiently. The intent is: 1) to offer a higher flowing 2 barrel for those short track classes that require a 2 barrel, but don't restrict what can be done to the carb, and 2) for the carb and carb adapter to bolt to a conventional 4150 flange 4 barrel intake. The first prototype has bored and reshaped venturis, modified downleg boosters , and a baseplate with a single oval throttle bore. With minor variations, this carb is flowing 840-850 CFM@3"Hg, when used with a 1" thick phenolic radiused exit oval hole adapter. In terms of its flow compared to a 4 barrel, it flows 600 CFM@1.5"Hg.
The reason for this approach is to get as much carb flow as we can into the plenum size of a 4150 flange intake, so that we don't lose the good low end characteristics of this type of intake. Keeping the mixture velocity up helps retain the mid range torque and driveability that is necessary for a short track engine to be competitive. The alternative is half a Dominator, which would need to be used with a Dominator flange intake, or with a funneled down adapter to adapt it to a 4150 flange intake. Either way, you end up with extra plenum volume. Half a Dominator would flow from slightly below 600CFM to slightly over 700CFM(@1.5"Hg), depending on venturi and throttle bore sizes.The Dominator design is not a particularly efficient design, because of the throttle bores being spread too far apart, and the rather bulky annular discharge boosters they typically have.
We feel that this approach of using the moidified Holley 4412 carb on a 4150 flange intake would give the engine all the necessary characteristics to be competitive, namely sharp throttle response on starts and restarts. excellent torque for acceleration on the first half of the straights, great top end power for the second half of the straights, and good driveability in the corners- a necessary feature to keep corner speeds up as much as the chassis set up will allow. Norm Schenck/ Competition Fuel Systems