[Carmine2]

Hi, I hope no one thinks this is too dumb a question, but I have to ask. In my '57 Belair, I'm running a 671 BDS blower on a 406 sbc. I have 2 Edelbrock 600's mounted on top. I don't know if this is the proper terminolgy, but the carb. linkage is "progressive"; both carbs. work together all the time. So, I have 4 barrels constantly feeding this engine. I knew it wouldn't be good on gas when I built it, so I can't complain about it. But, I didn't know gas would reach the price per gallon that it did either. I'm self taught with putting this arrangement together and would like to know if its absolutely necessary to have this type of linkage? If so, why? I appreciate your thoughts. Thanx, Carmine.

 

[jwmbishop]

syncroneous linkage keeps all barrels opening at the same rate - progressive will open primaries first, starting the secondaries later but at a faster rate to be equal at WOT. There is a way to hybrid this - that is both carbs primaries are synced but one carb opens its secondaries a bit faster - however -distribution problems will arise as the carbs opening rates are then not centered to the engine! the blower may correct some of this - but I am not sure on that part!

As an example look at a tri pack - with three two barrels. The center carb is primary - it has idle, enrichment accelerator and main circuits, while the front and rears have only main and accelerater circuits. The ends are synced together - progressive to the center. Imagine if the center opened - then the rear carb, then the front. during the intermediate when only the center and rear were open the front two cylinders would provide a MUCH weaker signal to the rear carbs air bleeds - resulting in leaning those two cylinders (or flooding the rear two to compensate!)

With two fours - you don't have a CENTER carb for even distribution during part throttle operation. therefore they are both primary and as such must both be syncroneous. So you will always run on four syncroneous and progessively tip in to 8 barrels (and the tip rate must be syncroneous).

You CAN however on dual fours make the secondaries progressive to the primaries at a faster rate, further into the primary opening (that is the second 4 don't start opening until the first 4 are further opened) - just a matter of the linkage ratios - but the rates have to be equal on both carbs! Getting them equal without a flow bench or dyno is very hard as you have to volume match not just at WOT - but through the whole throttle opening process. And its hard to find a tuner willing to ride on the hood with his sync guages during a run!

 

[Carmine2]

syncroneous linkage keeps all barrels opening at the same rate - progressive will open primaries first, starting the secondaries later but at a faster rate to be equal at WOT. There is a way to hybrid this - that is both carbs primaries are synced but one carb opens its secondaries a bit faster - however -distribution problems will arise as the carbs opening rates are then not centered to the engine! the blower may correct some of this - but I am not sure on that part!

As an example look at a tri pack - with three two barrels. The center carb is primary - it has idle, enrichment accelerator and main circuits, while the front and rears have only main and accelerater circuits. The ends are synced together - progressive to the center. Imagine if the center opened - then the rear carb, then the front. during the intermediate when only the center and rear were open the front two cylinders would provide a MUCH weaker signal to the rear carbs air bleeds - resulting in leaning those two cylinders (or flooding the rear two to compensate!)

With two fours - you don't have a CENTER carb for even distribution during part throttle operation. therefore they are both primary and as such must both be syncroneous. So you will always run on four syncroneous and progessively tip in to 8 barrels (and the tip rate must be syncroneous).

You CAN however on dual fours make the secondaries progressive to the primaries at a faster rate, further into the primary opening (that is the second 4 don't start opening until the first 4 are further opened) - just a matter of the linkage ratios - but the rates have to be equal on both carbs! Getting them equal without a flow bench or dyno is very hard as you have to volume match not just at WOT - but through the whole throttle opening process. And its hard to find a tuner willing to ride on the hood with his sync guages during a run!

Thanks John. I knew there had to be a reason for it. The blower and motor work well but as you know, gas prices are way up there. So, if its not broken, don't fix it. I've come this far and I can't let the price of gas affect one of my passions. Thanks again, Carmine.