Spacers usually run from $15-16 on up to $40 or so, depending on usage and materials used in the manufacture. You can find them as well in any speed equipment catalogue. There are spacer plates made to go under carburetors that can also enhanse power. Yes they do help increase horsepower as the air going into your carburetor isnt turbulent but flowing straight and orderly, allowing a fuller charge of air. You might just want to measure the diameter of regular tin cans and see if you can find one that has the right diameter, go from there. The ones I have are old tech from way back. The tobacco tins which I have on my 3 dueces, have the bottoms cut out and the top ring that the lid attatches to is in tact, so I will have a place to mount the air filters. As you can see they can be pretty simple, and are easy to make. Usually they are about 4-8 inches tall and made from a variety of materials. Some look like someone cut the end off of a trumpet, others are straight with just a flare at the very top. There are several versions on the market. Velocity stacks act to straighten out your air flow prior to entering the carburetor. Velocity stacks mount on top of your carburetor, not under it. If you are really interested in delving into the theory a little deeper, send me your email address and I will send you a scan of my senior project which was to design and build improved intake and exhaust manifolds for a Briggs & Stratton 5hp one-lunger. A velocity stack above a a carb will have little affect on port pressures since the carb internals will kill the pressure pulses. Your suggestion of building a plenum under the carb is in effect a tunnel ram manifold that will hurt bottom end performance but improve top end. That is a big subject and if you are really interested, look at these old treads discussing it, here and here (this one is specifically about exhaust tuning but the principles are the same).Īctually, every intake and exhaust design must take these dynamic air movements into consideration or they could actually hurt performance unintentionally. True 'velocity stacks' that have been used on port injectors for decades take advantage of the little pressure boost available from the 'organ pipe effect'.
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