Mechanical or Vacuum Secondaries?

[patrickt]

Originally Posted by caesarmascetti

thanks for the replies it's the one issue I hear both sides on, not sure what to do. I have vacuum secondaries on my 347 now and it runs very well

The only disadvantage of vacuum secondaries is that it can be a real PITA to get the opening "just right" because it involves switching out the spring in the vacuum canister. If you change your air filter housing to be less restrictive, you have to readjust everything or your car will actually run slower because the increased volume of air reduces the venturi vacuum that opens the secondaries. About eight years ago I installed a Quick Fuel Adjustable Vacuum Secondary Housing. Being able to adjust your secondaries' opening with a turn of the screw, along with being able to mark their opening with a zip tie, makes getting them right a piece of cake. BUT, it's still dangerous to do so on the street with a big block Cobra. It's really pretty simple, you just accelerate as hard and as fast as you can, and keep turning the screw so the secondaries open quicker, and repeating the process until you get a bog while accelerating, and then you close the screw back up a bit. To be honest with you, you really need a spot where there is nothing to hit, because any time you have your Cobra at WOT you really don't have full control over it. Anybody that tells you they have control over their big block Cobra at WOT on the street is lying to you. I've gotten old now, having had my Cobra for 15+ years, and I drive like a little old lady now. I might open the secondaries once or twice year. But I will tell you this, properly adjusted vacuum secondaries are absolutely the best way to go unless you do nothing but live on the race track.

Here's my old thread on the QF Adjustable Vacuum Secondary Housing. You might find it interesting: Theoretical Vacuum Secondary Question

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