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Discussion Starter #1
i would like everybody's opinion on this ,i run a 650 vacum secondaries which holley says is better,but are they talking everyday driver or drag car? my only interest is to go from point a to point b asap!
 

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Depends on a lot of other facters - engine, trans, cam, etc.

On an essentially stock engine, the vacuum secondaries will probably work better.

With a big cam, heads, and intake (with a low vacuum signal) the DP will work better.
 

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Vacuum secondaries only activate when enough vacuum is created in the venturis to open the secondary butterflies. This means the carburater decides when they open not your foot, as aposed to a double pumper which opens mechanically using linkage connected to the primaries. At a certain position of the primaries the secondaries open. Usually you can set/adjust that position. sometimes it means actually bending the linkage.
 

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Discussion Starter #4
my point was simply this,holley says that a vacum operated carb. will only pull in what gas the motor can use,whereas mechanical secondaries will cause a so-called dead spot where the carb. is putting out to much gas,but running a drag car what would be better?
 

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I'm not sure. That is definately true about the carb only pulling what it can use as aposed to you ''force feeding'' it fuel. I don't know if there is ever a time when vacuum secondaries can't pull enough fuel and you ''need'' to force fuel. I do know that when you are driving around town a double pumper will kick in and give you a kick in the ass that you just don't get from vacuum secondaries. I have never heard of a high HP drag car with vac secondaries.
 

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if you are going to drag race it, go with the mechanical secondary carb. even if you did have a dead spot you can tune it and fix that
 

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If you feel ther secondaries kick in - vacuum or mechanical - then you're tuning is off and you're losing power. Done correctly, it's a smooth transition.
 

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Discussion Starter #8
today i bought a holley mechanical carb.and it does make bigger power compared to the vacum operated,but i still think i could've done better with that carb by changing the springs and one day i still might try,it is hard to overlook holleys opinion of their carbs,i appreciate everyones opinion and i obviously took the majority.i would like to hear from someone who runs one.
 

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On a street setup, the vacuum secondary carb will help with fuel economy. For a race setup, mechanical secondaries are preferred, but I have seen both being used with success. BTW, it's not vacuum that opens the secondaries on a vacuum secondary carb, but rather the loss of vacuum.
 
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