**Randy Norian's thoughts on**

tuned inlet design for Motorcycles

tuned inlet design for Motorcycles

**thanks to Randy for letting me go public with this series of E-mails****QUOTE:-**

Oddly enough, I am pursuing this very topic (design of a resonant airbox) on another forum. I'll let you know if I get any good responses!

Here is from a previous post on this topic

OK, this is regarding my diesel, but just so you know I'm still pondering airboxes and this one is a good example.

Typical helmholtz resonators are a volume (airbox), fed by a duct of certain length and cross section. these 3 things determine the resonant frequency of the airbox. look at an RGV250 and you see a pair of inlet ducts, a few inches in length, that feed the airbox. shortening those ducts raises airbox rez freq. anyhow--

My TLS has a little flapper in the inlet duct, it closes at low rpm. to provide restriction? nooope- read on!

OK, I gave the TLS airbox my best analysis. (sat and stared at it) just how does the flapper affect things? The airbox is a CLASSIC helmholtz resonator, complete with entry duct (that is the tube coming up from the floor) . stock, I figure (flapper open) the duct length is approx 2.4" and area is approx 5 sq in. with a box volume of 550 cu in it resonates at approx 120 Hz.

flapper closed, sectional open area of inlet duct approx 1 sq inch, airbox now resonates at 53 Hz (low end boost)

remove flapper, you lose that variable resonance

shorten the inlet duct to 1" in length, resonance goes up to 184 Hz. cut it off completely and I'm not sure what happens?? This is a very clever bit of work. The TL has a weird double-gulp intake event every other revolution. I'll treat it as a single for simplicity- with flapper closed, the airbox resonates approx 3200 cycles/min, so you'd have a weaker resonance at 1600 rpm and then a stronger resonance at 3200 rpm. once the flapper opens, you have airbox resonance at 7200 cycles/minute -- so you get a weak resonance at 3600 rpm --and a stronger resonance at 7200 rpm.

All these resonators use a box with inlet duct of certain length. it's never just an open hole. There has to be a better way to improve things than cutting everything out of there.

One could apply this to an RG500 airbox- one on each side of the engine- sufficiently large... the use of a flapper could seriously aid low rpm power

Say we want a boost at 3000 rpm, where we have 6000 intake events/min we can shoot for a helping wave every other revolution (3000 cycles/min D 50Hz) treat each side separately- I think one could make an airbox of 400 cu in (0.23 cu ft) on each side. feed this through an inlet duct of sufficient size, - say - 4 sq in (.0278 sq ft) , , with a flapper that blocks it down to 1 sq in (.007 sq ft) . and length of... 3.6" that gives a resonance at 52 Hz. with flapper open, resonance occurs at 104 Hz (6240 cycles/min) and you get a boost in the midrange at 6200. or juggle the inlet tube length to counteract the pre-pipe flat spot anyhow, I'm still working on stuff... but my next effort will have airboxes that work!

**So long**

**Randy**

**http://homepage.mac.com/rg500delta/RandysAddiction/**