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Re: 2 circuit
Originally Posted by markdunlap
Guys, correct me if I am wrong.
Originally the annular discharge, 3 circuit dominator like 9375 was designed as a tunnel ram 2X4 carb combination. 3rd circuit was to help cover up the flat spot on a tunnel ram with their big plenum volumes. Then someone,(anybody know who?), found out the annular discharge boosters were better for some single 4 applications and the 3rd circuit just came along for the ride. Now all Dominators are Annular discharge but you get the choice of 2 or 3 circuit. Don't really need the 3rd circuit on any BBC unless tunnel ram? Maybe still needed on SBC? |
Actually the intermediate circuit was derived from metering blocks used in a Chrysler emission carb, the application was to use them on individual runner intakes where pulsing below the throttle bore is high. 4 and 6 cylinder engines can suffer from this, it disrupts booster signal at lower RPM's. Dominators running methanol can benefit as well with the right 3 circuit blocks (not factory blocks with the idle tube in the mainwell), not so much because of booster signal issues but as a supplement to the main fuel as passage sizes are on the border to pass enough methanol. For a V8 on gas it's rare an intermediate circuit is needed at all if you calibrate the carb correctly. Plenum intakes dampen pulses so there is no hole to fill when tuned correctly. I have run up to a 2.400 throttle blade billet carb with no issues running the intermediate circuit plugged. That carb flows over 1800 CFM...
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2 circuit
Thanks Mark, I knew you good for the correct info.
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This is what I found on the Holley website, contained in their Dominator instructions.
Inclusion of this circuit was required as a means of obtaining a smooth transition from the idle to the main metering system. It is intended to overcome a dip in the fuel delivery curve of the Model 4500 carburetor. Increasing/decreasing restrictor size delivers more/less fuel to enrich/lean the mixture for transition. |
Except there is no dip when the carb is set up correctly. Idle, transition, and main metering can be tuned to provide a smooth transition without it. The only reason it was added originally was for individual runner induction. Marketing told them if is two is good, three is better and will sell more. One for the bean counters.
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