Hi Mark,
Yes, I also considered the resonant chamber (also used on some motorcycles, which is my real background).  The resonant chamber would be lighter and maybe easier to build but I liked the 'tunability' of the separate runners for each rpm range.  If I need either shorter or longer runners I can change the length by inserting a longer runner connected with hose & clamps.  Also, I have the formulas (I used Ed's formulas) to calculate the tubing lengths and I don't have any idea on how to calculate the needed volume of a resonant chamber.  It is also interesting that some off road 2 strokes use a resonant chamber on the exhaust as well.  I haven't ruled this out yet but the butterfly would be living in a harsh environment ideed!  Maybe we should consider a resonant chamber on the exhaust in an effort to get the overall length shorter.  This would definitely be a research project for AFTER I get my RV-4 built and flying (which will be NEVER at the rate I'm going!).

Ken Powell


> Ken,
> This is directed at the engineer types in the group... What I was thinking
> is would you actually need two separate runners, or could you add a
> resonance chamber to the shorter intake so as to fool it into thinking it
> was longer than it actually was?  A butterfly valve could open and close
> the chamber.  I got this idea from studying the intake on my LS1 Chevy
> pickup.  It uses a resonance chamber in the intake between the air filter
> and the TB.  Not sure why, but though this same idea may work here too.
>
> Mark S.
> (back to lurking)
>
>
> At 02:19 AM 5/12/2004 +0000, you wrote:
> >Rusty,
> >I just gotta ask - why don't you just copy Tracy's intake and be done with
> >it???
> >
> >I calculated intake runner length for a PP engine last year but
> >unfortunately I don't have the results here in sunny Florida (playing
> >tourist, much to the chagrin of the natives).  So these numbers mean
> >nothing, but I THINK that I calculated that a 16" runner length for 7400
> >RPM (2.85 redrive) and 24" for either 5600 or 6000 RPM.  The problem we
> >are all seeing here (and Ed is addressing) is that we need several
> >distinct lengths to correspond to the differing engine RPM.  Since I am
> >dealing with a PP engine I am sorta on my on but Ed's work has been a
> >great help because his formulas will allow you to calculate the length for
> >a given RPM.  My thought on the solution to this is a little different
> >from Ed's infinitely variable length but simpler to build - since a PP
> >engine only needs 2 runners (1 per rotor) the idea is to have a short
> >runner (16") for high rpm and a long runner (24") for cruise; a butterfly
> >valve will be used to switch between the two.  I hope that this setup will
> >not need to be automated - set the butterfly to 'long' for takeoff, climb
> >and low altitude cruise and 'short' for WFO and high altitude cruise.
> >
> >Ken P.
> >
> >
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>
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