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post #37 of (permalink) Old 06-27-2019, 02:31 AM
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Join Date: Jan 2019
Location: Sedgwick, Kansas
Posts: 689
Double pumpers are awesome on the strip. But vac secondaries work sort of like a 'variable venturi' carburetor. At low RPMs, when the engine is not pulling much vacuum at WOT, you get excellent atomization through the primaries. Then, as needed, you get more from the secondaries - again, with proper atomization.

If you're running a double-pumper with steep gears, and/or running a manual transmission, you get into higher RPMs so fast, there's not too much of a penalty for the poor mix quality; you build RPMs and then the carb can atomize well even with all 4 venturii roaring along.

On an automatic running highway gears with a stockish torque converter, you are often put in a situation where the initial spurt of gas from the accelerator pumps gets burnt, all 4 barrels are open, but the engine is still at low RPMs, and not drawing much air. At this point, most double pumpers will be raining big fat drops of gas down the intake, and even if you don't have a bog, that's not great for performance or for economy.

For an automatic-equipped car, destined for use on the street, I much prefer a carb that's going to deliver snappy performance no matter what my RPMs are at. I've seen some really nasty strip terrors that could not break the tires loose in first gear, from a rolling start (without dipping the clutch). I've used a lot of carburetors, chasing performance, economy, or both - but always with street use in mind. My favorite by far is the old Autolite 4100 and its newer descendants. I used to really make my buddies mad. Lining up against their 350 Rocket '72 Cutlass Supreme, 73 455 Buick Riviera, 71 400 GTO convertible, and '70 Super Bee 389, my little 302 would always stomp 'em, and they never could believe how eager my car was to 'go' from any speed. Though to be fair, Dave always really babied the clutch and granny-shifted his Bee.

A huge part of that was my old Autolite, because I sure didn't have the money for a torque converter or hot cam at the time.

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