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The velocity aspect seems to carry a lot of weight in rotary tuning. The reason I say that is my best power (thus far) has been with the smallest diameter tubes. I have used TB with up to a 75MM opening and have found them providing less desirable throttle response characteristics. Not to say that large diameter tubes and throttle bodies don't have their place. My personal opinion is that until you are talking 9000+ rpm err on the side of smaller diameter tubes to keep the velocity up. Tracy has hit 7200 rpm with his small tubes with his 2.85, so I would think its a bit premature to worry about the 1.75" being restrictive. Most credible studies/theories on intake tuning put a lot of emphasis on intake runner velocity, in fact most quote a not to exceed velocity of Mach 0.6!!! I believe that is the peak air velocity of the surging intake charge while the average velocity is considerably lower.

Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC

----- Original Message -----

From: Russell Duffy

To: Rotary motors in aircraft

Sent: Tuesday, June 01, 2004 10:23 PM

Subject: [FlyRotary] Re: Rev-2.1 part 2

Do you think 48-50mm's would boost power? Mo mix? The allout Racing Beat wrap around intake uses 48MM Webers or Dellorto carbs. Dave Atkins is really estute with that rig, so what does he say?

TJ

One simple theory says that the largest throat possible will decrease air flow resistance, and let the MAP get closer to the actual ambient pressure. This ignores the more complicated theory that says that higher velocity air through a smaller opening will help stuff more air in the chamber. Everything is a compromise, so your best results will be somewhere in between tiny, and huge. Ed will calculate this for you, since he has no flying plane :-)

Seriously, my 40 mm (which I didn't chose) has the same ID as the 1.75" OD tubing that I used for runners. I doubt they're causing me any problems now, but I do worry that it will be somewhat restrictive when I get to the -C drive, and 7000+ rpm. If I end up matching Tracy's static rpm with this setup, it will be interesting to see how I do with the higher rpm configuration.

If you want to know what Dave has to say, give him a call. I've had my last conversation with him.

Cheers,

Rusty (low tolerance for BS)