Finn Lasses wrote:

Thanks for the chart, Paul.

Now, what about a two-rotor system. Is there any power
advantage/disadvantage of running separate pipes/mufflers vs. joining
them very near the ports?

I'd hate to add more weight than absolutely needed. Least weight would
be making a Y close to the ports and running a 2" pipe from there.

BTW, Ed, I don't see any flex points in your system?

Finn

I would run separate pipes and separate mufflers like Ed did. I think
you could use 0.035 316 SS. By the time you get back to the mufflers
the exhaust should have cooled off a bit and they should last longer
than 1000 hours such as Tracy got out of his. 16 pounds seems a lot
for mufflers. I like your idea of opening the front of the concentric pipes.
That should cool the guts without increaseing the noise too much as
the slipstream should flow a lot of cooling air through there. This is a picture
of the early Power Sport engine with the 30 inch tuned pipes.

Finn Lassen wrote:

Well, by only running 1 pipe most of the way and only one muffler, you could cut the
weight almost in half.

2" .035 SS pipe is .74 pounds/foot.
3" .035 SS pipe is 1.1 pounds/foot.

A simple one pipe/muffler system could be: 1' + 4' of 2" and 1.5' of 3" =  5.4
pounds plus flanges, mounting HW and welding rod; if I start the 3" pipe just after
the firewall.

Also, I'm beginning to think that the less exhaust pipe surface area you have under
the cowling, the less radiated heat you'll have - another advantage of a single
pipe. Might even justify going from 2" to 1.75" pipe?

A single pipe would probably run hotter. The heat rejection is the same from
the engine. Come out the side of the cowling and run them down and along side
the aircraft. Same drag as out the bottom. It would sure look cool :-) PL

The big question is, in addition to length, if you join the two exhausts do you get
a scavenging effect? The flow from one rotor's exhaust pulse helping to suck out the
exhaust from the other rotor. If so, how long do the headers need to be (before
joining at the Y) at say 6000 - 6500 RPM?

31 inches. If it gives you 15 more HP is is worth 5 pounds? That is three HP per
pound which is a way better ratio than your engine provides. That is the 10% 
difference between a properly tuned pipe and a poorly tuned pipe based on 150 HP 
to start. Probably with better BSFC in the bargain which will easily pay for itself 
in short order at today's gas prices. PL

I hope I'm not stretching your patience too far, but it's a lot easier to bounce
these questions around before I commit to materials and work.

Finn

 
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