Hi all,

I've recently discovered the use of the so-called "velocity stacks", mainly for gas engine conversions and similar sized engines. They all appear to be a tube bolted to the carb intake, with the end cut at 45º facing the airflow, so prop blast is forced into the carb - creating a sort of forced induction effect.

I'd like to know if there's a noticeable perfomance increase with that mod, as well as possible design considerations. I hope I don't say too many stupid things, but:
- The tube seems to have the same internal diameter as the carb, but why not give it a different shape? Why just no use a 90º elbow instead of the 45º cut? Will I gain something if I try what I've seen in bikes - cone or trumpet shaped carb intakes.

I was going to turn a simple velocity stack with my lathe but would like to know if it's worth the time and if other shapes are worth a try.