View Full Version : Down Leg vs. Annular Boosters
01-10-2006, 02:36 PM
My old carbs had "downleg" boosters. Newer carbs offer a choice between downleg & annular boosters. It seems to me that the downleg boosters are a bit smaller and don't detract as much from the carbs CFM rating. Are there advantages to using "annular" boosters? :question:
01-10-2006, 06:54 PM
I see you run a 406. Tell me more about your combo. I run what must be a similar set up, 406, Camaro, I had the best times with a box stock, rejeted 950HP. I tried a 830 annualar set up, ran good, but not as good as the 950HP. Tried a tricked out Biggs (borrowed), no better, no worse.
01-10-2006, 08:30 PM
From what I understand annular boosters allow you to run a bigger CFM carb so that you can have it for the airflow up top and it maintains the lower end of the RPMs better.
01-10-2006, 11:34 PM
Boosters pull fuel out of the main well via vacuum signal in the main bore. Boosters are actually a second venturi, and the smaller bore, coupled with lots of small holes around the ID (aka annular) let it react faster and more crisply in a carburetor that's "too big" per usual thinking.
Like the above two posts, if you have enough motor to require a 950, but that much carburetor doesn't work well (is mushy) at lower RPM levels, then a change to annular boosters will likely help.
01-14-2006, 12:25 PM
Thanks guys! According to everything I've been reading on this topic, the annular boosters should offer a bit more throttle response than a down leg booster on the same size carb. While perhaps cutting down the CFM rating a little.
I'm in the middle of building a radical street motor (500+ cid) and a "Dominator" is just too close of a fit under the hood. They do make "down leg & annular" 4150 style carbs that flow up to 1050 cfm that do fit. I guess the annular boosters will help to make the motor a little more "streetable!" :D
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