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Discussion Starter · #1 ·
What's the difference in performance between a carb with vac secondaries against a carb with mech secondaries? ... BTW great feedback on the Edelbrock vs Holley thread...Thanks for the input.
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Paul
 

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Mechanical secondarys can be tuned as to when they come in and how fast. You don't have that tunability with vacuum secondaries. Generally, mechanicals work better for race conditions. Vacuum are better for street where racing is notinvolved.
 

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Too many varibles to give a specific answer to a questions like this. The compression, camshaft, intake, rpm, etc all play into what carb is best.
 

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I disagree about the vacuum secondaries not being tunable.You can buy a spring kit to change at what rpm and how fast the secondaries open.Removing the check ball is also sometimes useful if the secondaries are opening too slow.The mechanical secondaries let you control when they open with your foot and are usually more suited to 4-speeds and or high performance or race cars.Vacuum secondaries are more forgiving if you have a little too big of a carb and will also give you better mileage on the street.
 

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I also prefer vacuum secondaries for the street. You can tune them in pretty good with the spring kit. I would recomend the quick change spring kit. Mechanical secondaries are good for small cars with a stick and drag cars.



Blue Fastback
 

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Edelbrock carbs are considered the best street carbs right? I was told that all edelbrock carbs are mechanical secondary. So how is a vacuum carb better on the street as far as performance goes? Im heavily considering a road demon which is a vac carb. what do you guys think?
 

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Discussion Starter · #7 ·
Ebrock are mechanical, Holley offer both. BTW Carter appears to be returning to the performance carb business. In this months Summit catalog, Carter are showing some products. I wonder how the Carter's will perform straight up against Ebrock (considering Ebrock use Carter carb bodies).
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Paul
 

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Ebrock carbs are not mech. secondary...All Ebrock's are vacuum secondary....The secondary throttle plate is mech..but air flow threw the secondary is controled by the air valve.....These valves are located in the secondary bores above the throttle blades.....They are balanced against a counter weight and open to admit more air flow only if there is enough air velocity to allow the proper operation of the secondary metering system....
Russ...
 

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Discussion Starter · #9 ·
I stand corrected.....but.....when talking mechanical versus vac, are we not talking about the linkage on a carb, and not the air flow?
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Paul
 

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Look in a Ebrock carb...On the secondary side there is four butterflies....two on top that are vacuum operated and will only open as much as the engine needs....The lower butterflies are connected to the primary's by mechanical linkage..when the primaries are about 65% open the secondary start to open and arrive at WOT at the same time...In the event that the engine does not need all that air the top butterflies will not open

Russ....
 

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Discussion Starter · #11 ·
AAAAAHHHHHHHHHHH I see. Thanks for the explanation.
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Paul
 
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