Vacuum secondaries and paxton?

[latamud]

Can I use my speed demon 650 with vacuum secondaries with a blow through application? Or would the boost and the vacuum zero eachother out? Is a mechanical secondary carb my only option? Thanks

[sscamino]

From what I've read about that setup, it is theoretically possible that it would work. The pressure differential is still present and should allow it to function. How effective this setup would work is questionable however. With the little bit of investment, I think I would go mechanical just to ensure that you never run lean under boost and that the carburetor is correctly metering the air/fuel ratio.

[latamud]

Thanks for the reply. I guess so. I just won a demon carb on ebay but turns out it has vacuum, couldn't see from the pictures on ebay. I'll find a mechanical.

[fanglemeister]

You can run it almost as is (with bigger jets in secondaries, nitrophyl floats etc) if you run the carb in a full enclosure (called a pressure box). If you wan to run a "hat" on top of the carb, you would have to reference the secondary diaphragm to boost to make it work, so like you said, much easier to go with mechanical secondaries. You are still limited to under 10 psi boost because carbs are not capable of dealing with high-density airflow. The best bet is to go with a draw-thru system, but then you run into startup mixture problems, etc.