Thanks Dick for your thoughts. When I first saw the ZDZ-40 RE with the velocity stack, a bell went off in my head. I was hoping that ZDZ would start selling the stacks as an option. I also found out that 3W has a velocity stack for the 3W-100 on Aircraft International's website that should also bolt up to the ZDZ-80. They get $17 for it. I plan on putting the stack on the carb and maybe adding a section to it to get the desired length. You're right that spinning it out of aluminum would be a cheap way to make it. Actually you could draw it from a flat plate in a die, but the tooling would cost more. Certainly it could be CNC machined, but you'd be wasting a lot of metal. Some of the older guys might remember V8 Chevy racing motors with Weber carbs, a single venturi and long intake tube for each cylinder with the stack on top. Same thing all over again. I'm sure you are correct about the exhaust system being critical to the power, but for my H9 Cap I'm just going to use the J&A Pitts, purely for convenience. I've got my buddy Hyper Tom convinced on the need for a K&S system for his new Aeroworks 31% Extra, and EJB is building the plane for him. Tom needs a quiet plane for Imac.

Another random thought - Have you tried modifying the intake rotary valve timing? Many years ago Kawasaki made a hop up kit for their Bighorn that used a longer opening for the rotary valve, along with a pipe and carb jets. I know we're not after HP at high rpm so maybe this isn't the way to go with longer timing.

Which model of Walbro carb have you got on the 80? There's a wealth of info on carbs from a fellow named EC Birt. He has a lot of experience with Tillotson, Walbro and a few other makes of carbs. Check out www.eccarburetors.com If you are getting better results from a different brand of carb, this fellow probably has the knowledge to explain why.