Canisters or Tuned Pipes??

[KrisW]

	Quote: Originally Posted by HTSkywalker
	Get the right engine size and go stock. A DA85 would cost only $200 more then the DA50 with additional 4 HP on stock muffler !!!

Okay. .you are comparing Pears and Kiwi fruit here. the "Class" of the two engines is totally different. I don't know anyone who would put a 50 on a 100+ inch aircrft, or an 85 on an 84" plane (though some probably will. . . )

When comparing similarly sized, or purposed, engines, there is a grey area of displacement and weight that can actually yield a slight advantage tot he lighter, smaller engine on a pipe setup. Start with price. . add in weight savings. . .think about simplicity (twin versus single setup) and then take a hard look at what you actually NEED. . .and what everyone tells you is the "hot setup".

I've been using the smaller 110-115cc BME's in 40% planes for years, because the canister exhausts and lighter weights enable me to achieve a suitable power-weight ratio. That people are using the 80-85cc engines in the "100cc class" planes is the same principle. It works. . it works well, and it's a lot less expensive and easier to do than with a twin setup, in most cases.

That's what most of this debate is about. Should you go with the smaller, lighter, piped setup that costs a bit less as well. . . or should you go for the noisier, heavier, more expensive setup that yields more top end power but adds a lot of unnecessary flabola to the plane?

Remember, we fly at WOT for about 5% of the time. The other 95% of the time the gonzo top end power of the larger is not necessary, and the weight of the powerplant becomes more critical for the overall flyability of the plane. For IMAC, this is a major consideration, since so little time is spent at WOT and the rest of the time you are trying to be smooth and precise, and any advantage you can get form lighter components is a big plus in how the plane flies. For your average 3D fanatic and barnstormer the factors of NOISY, overpowered, and easy, take precedence over quieter, adequately powered, and a bit of effort involved.

Pick one, they both work. but there are advantages to each, as well as disadvantages under certain circumstances.

[KrisW]

	Quote: Originally Posted by dick hanson
	Kris got it right !!!!!!!!!!!!!!!! torque differs, depending on the exhaust setup Said differently - the max torque occurs when the engine can be made to inhale the largest fuel charge---and you can move that point in the rpm band. Here is the tricky part - you may want to , move it further up the rpm curve. MAX torque may now be smaller but more effective at some point higher up the rpm band. getting breathing right is not as obvious as it looks. -it isn't just rpm and pipe length - it is also PRESSURE and volume in the pipe . (which none or few of the "experts " ever mention. Those fu--in books on how to tune pipes mostly suck - for our use. once you get it right it really changes things As an example : the pipe setting I use to get 6600-6700 on a 27x10 on an 80 JZDZ(true) is not the same max setting for a 26x10 prop - it is too long but the plane I have it in works best with this setup changing the pipe the rpm then on a 26x10 goes waaaaaay up but so does noise and all in all not the best match for that model. If this does not make sense ---- forget it --- use what you find best for you .

Dick, you need to stop agreeing with me. . it's confusing people. . . .

But concerning different pipes on the same engine, depending on application. . . .in my Comp-Arf superXtra I used the KS-1080 pipes on my DA-150, and swung a Biela 30-12 THREE blade at 5400 rpm on the ground. The performance was so strong I actually dialed down the top end throttle, because the plane was ballistic in the air. I'd dial it back up a little bit for high wind conditions, but mostly 3/4 throttle was the optimum top end setting for the engine.

Conversely, in my much heavier, and draggier, Wild Hare 41% 300 I use the exact same engine, but went to KS-1090 pipes and a smaller 29-12 3-blade Biela at 5850 rpm to get more thrust to help pull the plane, and I still don't need all the power, as I am backing off the gas on most up lines, but it's necessary for those vertical snaps, so I keep it on tap.

Exact same engine, totally different focus for exhaust tuning and prop, all because the airframe changed. The KS-1080's are about 100 rpm weaker than the KS-1090's using a Mejzlik 32-10 prop, but they create a much smoother mid-range and are less peaky, which made IMAC flying much easier. I find I actually prefer the way they made the engine run. All because of the shift of focus toward the mid-range of the rpm band, instead of going for maxed out top end rpm numbers.

[HTSkywalker]

Kris you are right on this, staying within your airplane engine envelop would yield more precision. But some of my colleagues likes rocketing around !!

[KrisW]

	Quote: Originally Posted by HTSkywalker
	Kris you are right on this, staying within your airplane engine envelop would yield more precision. But some of my colleagues likes rocketing around !!

I have a 3W 240 sitting on the shelf here, if they REALLY need some more power. . . .

[adrian]

	Quote: Originally Posted by RustyTumbles
	That is the best explaination I have ever heard on exhaust systems.

lol - you dont know about Dick Hanson???? he's the pipe man!!

[forgues research]

So tell me, aren't some engines not designed for tuned pipes, and some are, what are the differences???

Kris, keep your answer under 12 pages

Roger

[KrisW]

	Quote: Originally Posted by forgues research
	So tell me, aren't some engines not designed for tuned pipes, and some are, what are the differences??? Kris, keep your answer under 12 pages Roger

Simple, Roger. . port timing and overlap, but they all benefit from a properly tuned exhaust system.

11.97 pages to go.

[forgues research]

	Quote: Originally Posted by KrisW
	Simple, Roger. . port timing and overlap. 11.97 pages to go.

Good answer, but doesn't this mean not all two strokes would benefit from tuned pipes...?

Roger

[KrisW]

	Quote: Originally Posted by forgues research
	Good answer, but doesn't this mean not all two strokes would benefit from tuned pipes...? Roger

No. It's a matter of degree and design. 2-strokes operate under the principle of "more out, more in" and the exhaust is extremely powerful in determining how much air-fuel is pulled into the engine, and at what rpm the resonance for maximum torque takes place.

11.9 pages to go.

[adrian]

in my experience(humble)the ZDZ's and 3w's respond better to tuned muflers than the DA by % because as per the above gentleman's explanations - no?? not sure about the EVO's, Roger

[dick hanson]

A rotary valve ( front/ rear whatever) is best for tuned stuff because you can do a
"tailored" intake flow.
On our old glow engine , we, as well as a thousand others , tried advancing the windows - widening them, on n on and in general -- ruining some engines ---- but that's how you learn.
The one thing I did find -then that you had to be able to control the "ignition" point -which on glow can be a pain, as temp changes that.
For max rpm only, a piston port is fine - reed valves- another ball game as you have to get the reed "resonance" right . They all work - for our use ( aerobatic powerplants) the actual effectiveness of reed vs rotary vs the pistonport - is also changed by the type of porting in each design - the huge cross flow ports look to me to be the best. The latest designs all use some variation of these.
One funny thing -you can actually get more rpm in an unloaded shallow dive with non piped stuff (open exhaust.) Not more power - just more revs - One day at the field I watched a guy with a glow setup keep leaning his engine to get the highest possible revs out of a split S.
He figured the "scream" was more power on display - sorta like prop rip - -or playing cards in bicycle spokes or blocking the heat risers on a car --
the theory(?) noise= power -

[HTSkywalker]

As an old fart in our club keep saying "an engine without a pipe is like a man without a d..k"