More on so-called Tuned Exhaust

[doug8082a]

Been there, done that, got the t-shirt. Let's not start THAT up again...

[N2255D]

Here's an story by AMT(Aviation Maintenance Technology)magazine on the subject.http://www.amtonline.com/publication/ar ... =1&id=1502
Too bad it sounds so much like an ad.

[Bruce Fenstermacher]

You know George, that sure was an evil plan of Joe's bringing up the Power Flow thing again. Wonder how he knew I would comment on it leading you to spend a lot of your quality airplane polishing time responding to the thread.

Before you know it it'll be time for the big race with Joe and you won't be as ready as you could have been. Not that it would make a big difference but you do want to put on a good showing.

Yes sir that truly was an ingeniously evil plan of his.

Just can't figure out how he got Walt to bring up the BIG 3, Mogas, 100LL and MMO.

[N1478D]

[mvivion]

George,

Wait--the induction lengths are different on an aircraft engine??????

Wow, what a coincidence---so are the exhaust tube lengths on one of these tuned exhaust systems!!!!

I can't believe it!!! The designers of these systems must have consulted with you about this very subject, eh?

I'm not an expert on this subject. But I have done some inquiries of people I trust, and who are absolutely independant of the manufacturers of these systems.

But, I forgot, it wasn't invented by Cessna in 1952, therefore it can't possibly be worthwhile.

Mike

[zero.one.victor]

Anybody up for a discussion on auto vs avgas or maybe MMO ?

Let's be more specific: how about a discussion on:
A) wheel-landing a 170 with tuned exhaust burning cargas with mystery oil
versus
B) three-pointing a 170 with stock exhaust burning avgas
versus
C) crashing a 170 with a leaky exhaust that ran out of gas

Let's not forget to imply that filing a flight plan could have prevented #C.

Eric

[GAHorn]

George,

Wait--the induction lengths are different on an aircraft engine??????

Wow, what a coincidence---so are the exhaust tube lengths on one of these tuned exhaust systems!!!!

I can't believe it!!! The designers of these systems must have consulted with you about this very subject, eh?

I'm not an expert on this subject. But I have done some inquiries of people I trust, and who are absolutely independant of the manufacturers of these systems.

But, I forgot, it wasn't invented by Cessna in 1952, therefore it can't possibly be worthwhile.

Mike

Hey, Mike,....let's agree to be respectful and courteous to one another. OK? The tone of some msgs aren't conducive to respectful disagreement, and the electronic word is already full of mischief in that regard.

As for your latest response:
And your point is...?
Yes, the intakes are different lengths,...and so are the OEM risers (at least the #1 and #6 are)...but so what? Differing lengths don't automatically equal "increased backpressures" that need relieving by "tuned exhausts" in order for the antiquated engines to suddenly become modern dynamos of power! If all you can get is 2330 static, and if 2330 static is the standard by which the limits of certifications are limited by the type certificatte, and if specific rpm equals a specific horsepower (i.e. if 2450 equals X%, and 2450 is what we use for cruise) then there's nothing any mfr of magic exhuasts can do to change the relationships.
This topic is an excellent example of how a discussion of theory cannot be found to support reality. In theory a tuned exhaust is an efficiency improvement. But, as you imply....even when attached to a 1952 design? I don't think a magic exhaust on a 170 is an "efficient" or judicious use of money. In reality it's a dud.

Speaking of theory VS reality, (you may have heard about this one):
There was the case of the father reading the daily paper after a long day at work, when his son came down the stairs and said, "Hey, Dad! This economics course I'm taking has me puzzled. I've got to give a presentation in class tomorrow about the difference between economic "theory" and economic "reality". Can you help me find an example to use?"
"Well, son, here's what I suggest. Run upstairs and ask your mother if...there was no way anyone would ever find out about it....and if he offered to give her a million dollars....would she sleep with the physical fitness instructor that's our next door neighbor."
So the son runs upstairs and asks the mom, "Hey, Mom....." (and he asks the question.) She thinks about it a minute, and says,..."Well, I guess if no one ever found out, then it wouldn't hurt anyone... I guess I might." The boy runs downstairs and tells his father, and the father says, "OK. Now,...run upstairs and ask your sister the same question. Ask her if no one would ever find out,...would she sleep with the next door neighbor's football-star son...for a million dollars?"
So the son runs upstairs and asks the sister, and she thinks about it a minute, and replies, "Sure! If no one ever found out...sure I would!" The boy runs downstairs and tells his dad.
So the dad says, "Well, there you have it, son. That's the difference between economic "theory" and "reality". You see, in "theory"...we're sittin here on a couple of million dollars!
But in reality ... we're just living with a couple of whores."

[N170BP]

Reminds me of a variation:

Guy asks a gal at the bar if she would be willing to sleep
with him for a million dollars. She thinks about it a bit,
and says "Well, a million bucks is a million bucks! I guess
I'd have to say I would sleep with you for a million bucks!"

He then asks her if she would sleep with him for $50 bucks.

Her response: "Hey now, what kind of a girl do you think I
am!???"

His response: "We've already determined what kind of gal
you are, now we're just haggling over the price!"

[Bruce Fenstermacher]

Eric- very nice responce

George- In response to Mikes post, you have said here at the forum maybe in not the same words that Cessna would have built it that way it if was better.

George I might have missed it here but are you saying you don't believe a turned exhaust times the pulses of the exhaust to help extract exhaust and in fact depending on the valve timing even supercharge an engine works in ANY application?

If that is the case I must tell you that in my modeling days I personally used and saw significant performance gains from a tuned header/muffler combination of the stock muffler which was nothing but a tube.

As for our aircraft engines and their application with the restrictions of regulation we live with I can see your points but am not sold on the fact that there couldn't be any benefit.

And finally George that was a neat story.

[GAHorn]

1) Bruce, you may have been thinking of blueldr's comment re: Cessna would have done it etc.....
I would say that if tuned exhausts were cost effective that Cessna would likely have done it though.

2) Bruce, let me respond by saying this: If the firing order of the engine is 1-6-3-2-5-4, and if 1-3-5 are all on the same right-hand exhaust sytem and 6-2-4 are all on the other, left-hand exhaust system.... Then exactly which exhaust stroke will be attempting to pressurize which adjacent cylinder's exhaust stroke? Answer: none. All cylinders sharing the same exhaust system have their exhaust strokes well spaced apart from each other. There is no opportunity for two cylinders sharing an exhaust system to compete against each other. (While any cylinder of a 3-cyl bank is exhausting the other two cyls are either on a compression stroke or a power stroke.)
Since there is also no individually tuned intake system, there is no advantage to tuning the exhausts to match either. A lot more change to this engine would be necessary in order to take advantage of a tuned exhaust. Tuned exhaust on this engine is not cost effective.

3)Did your models have an individually tuned exhaust matched to a cylinder with an individually tuned intake? (i.e., was it a single cylinder system? If so, then the individual exhaust was indeed matched to an individual induction system and tuning that exhaust would have been easier and with more likelihood of cost-effective benefit.)
I'd also suggest your experience would most likely fall into the category of anecdotal evidence. Models that I've observed are commonly equipped with side-exhaust, but those with modified exhausts (so-called tuned exhausts) were directed rearward with performance benefits derived from recovered/directed thrust....more than actual engine performance increases.
They were also 2-stroke engines where every upward stroke of the piston was a compression stroke in a cross-flow breathing cylinder running at exceptionally high rpms, where tuning is not just a benefit but absolutely mandatory. (Not anywhere near an apples-to-apples comparison.)

[mvivion]

George,

No offense meant, and not to worry.

I can see no point in posting messages to a forum which is operated by one who shouts down any opinion that isn't warmly accepted by everyone on the list.

Sure does cut down on information exchange.

Mike Vivion

[lowNslow]

George, the intake and exhaust efficiency are two seperate issues. While you would also see improvements with tuned intake - it would not effect the efficency of the exhaust cycle.
The theory of the Powerflow system is it improves the exhaust cylcle by reducing the hp required to expel the gasses and improve the volumetric efficiency by expelling all the exhaust gasses. This would probably be achieved by combining BOTH banks of cylinders into one collector/extractor. I would guess you COULD get a modest improvement with this engine, but either way, I agree it would not be cost effective.

[zero.one.victor]

It's my understanding that the Lycoming 170 installation (which the Powerflo is approved for) DOES collect all 4 exh's into one muffler )aka collector).

Eric

[Bruce Fenstermacher]

1) Bruce, you may have been thinking of blueldr's comment re: Cessna would have done it etc.....

I stand corrected.

I would say that if tuned exhausts were cost effective that Cessna would likely have done it though.

You never answered my question if you thing a tuned exhaust works in any installation. Your view that Cessna would have done it had it been cost effective leads me to believe you think there might be some benefit.

2) .... Then exactly which exhaust stroke will be attempting to pressurize which adjacent cylinder's exhaust stroke? Answer: none. ...There is no opportunity for two cylinders sharing an exhaust system to compete against each other...
Since there is also no individually tuned intake system, there is no advantage to tuning the exhausts to match either. A lot more change to this engine would be necessary in order to take advantage of a tuned exhaust...

A tuned exhaust works on one cylinder. That for which it's tuned. It is not dependent on other cylinders or firing order.
The advantage is that the exhaust is sucked out of the cylinder better than just being pushed or worse forced back into the cylinder from the exhaust system back pressure (if any). The effect leaves the cylinder with more clear volume to allow more fresh fuel/air regardless of the carbauration for that cylinder. Of course if the cylinder was running so lean before hand there would be no advantage.

Tuned exhaust on this engine is not cost effective.

I have never argued this point. The list of non-cost effective modifications on aircraft is long.

3)Did your models have an individually tuned exhaust matched to a cylinder with an individually tuned intake? (i.e., was it a single cylinder system? If so, then the individual exhaust was indeed matched to an individual induction system and tuning that exhaust would have been easier and with more likelihood of cost-effective benefit.)

My engines where single cylinder 2 stroke. The carburetor or induction system was not changed from stock. When properly tuned the exhaust would conservatively add better that 10% as I recall. At 8000 rpm that's nearly 1000 rpm. A lot off engines ran faster and gained more rpm. The exhaust would often times be half the cost of the engine. In the case of a model 2 stroke engine the exhaust pulse would actually draw the fresh fuel charge into the cylinder and exhaust system then after the intake valve closed ram the fuel back into the cylinder super charging the engine.

I'd also suggest your experience would most likely fall into the category of anecdotal evidence.

No George it was measured using electronic tachometers and very evident through flight performance. The practice is so common in precision aerobatics that to be competitive you must have a tuned exhaust.

Models that I've observed are commonly equipped with side-exhaust, but those with modified exhausts (so-called tuned exhausts) were directed rearward with performance benefits derived from recovered/directed thrust....more than actual engine performance increases.

I've been inactive in the modeling world since about 1990. Till that time there was no exhaust system that created ANY thrust. I had a tuned exhaust on a helicopter and it didn't create any thrust. It did create quite a bit of torque differential as the "pipe" tuning came on and of with RPM. At the time helicopters hovered just over half throttle just about the rpm the "pipe" timing came in.

They were also 2-stroke engines where every upward stroke of the piston was a compression stroke in a cross-flow breathing cylinder running at exceptionally high rpms, where tuning is not just a benefit but absolutely mandatory. (Not anywhere near an apples-to-apples comparison.)

I've never been discussing an apples-to-apples comparison here. This particular "round" of discussion started because Joe poked fun at Power Flows theory of operation and I pointed out it wasn't garbage.
I've never argued that it even works in our application or is cost effective. I do know that unless it doubled my power and cut my fuel bill and probably even then I'd never hang one of those ugly things on my plane.

VGs, Mogas, MMO, re-arched dual main tail springs, big tires YES.

Besides I don't need extra poer when I'm cruising "On the step"

[GAHorn]

"You never answered my question if you thing a tuned exhaust works in any installation." A'contrere, my dear Bruce. I did indeed remark/imply how individually tuned exhausts are beneficial when mated to tuned intakes.

If I understand the way it stands, we are in agreement that in certain circumstances a tuned exhaust is worthy. The circumstances I personally subscribe to are 1) a cross-flow 2 stroke engine (where a tuned exhaust is not a luxury ...but a necessity for the engine to run. Particularly those using a "reed" type intake valve and ported piston. Even if only an open port...it is still "tuned" to allow the engine to run, and any appreciable de-tuning of the exhaust will shut it down.) 2) High rpm racing engines (primarily on autos, not airplanes....due to propeller limitations, ...not to mention weight, and drag.) 3) 4-cycle engines which have intake/induction systems individually connected to individually tuned exhausts (also known as tuned "headers"....at least to the point of a "collector" placed sufficiently downstream to augment the exhaust. Unlike the 2-stroke, a 4 stroke engine will run with a considerable amount of detuning....in fact it will run to the point of pressurizing the exhaust up to virtually the same pressures as the compression pressures reached at T.D.C. which hover above 100 psi !)

Except in the case of the 2-stroke....there is no convincing me of any "vacuum" or "suction" (i.e. "sucked out of the cylinder ") existing in any exhaust system..tuned or not. Thinking of a manifold pressure gauge installed in the exhaust system anywhere along it's length will quickly prove the point, I believe. The discussions we've had regarding vacuum systems...using airborne-type fittings, hoses, and elbows....will illustrate the types of improvements that can be made to an exhaust system. Any mfr who makes those simple improvements can refer to their systems as a "tuned" system if they wish for marketing purposes. But that is not what many people envision when they start imagining things like "suction" in an exhaust system, or back-pressure due to forward facing tailpipes or super-duper motor oil additives like Teflon (c) and similar marketing successes the public falls for. (I'm always amazed at the number of poeple who will purchase an oil additive with that stuff in it...believeing it's reducing friction and adding gas mileage...never considering that if their oil filters are any good at all they've filtered it out very quickly...hopefully without clogging.)

It becomes a matter of how much one is willing to believe one's imagination. IMHO