PowerFlow Exhaust on a 170

[inman]

I see pictures once in a while of 170s with the Power Flow exhaust. I am interested in hearing any feedback from anyone who has done it. My 52 "B" model has the Avcon 180 HP conversion and everything I've read in the magazines makes it look like a great upgrade to the 150 and 180 horse Lycomings in 172s. I emailed PowerFlow and asked if there was any approved installations done on 180 horse 170s and they never answered.

[N1277D]

There is a 170B in Northern Idaho with this set up. He indicated that there were only three of them done on 170s before Powerflow stopped selling them outright except for the correct STC'd airframe engine combination. The story goes he ordered the exhaust for the engine as an experimental setup and took his 170 to Alaska and got it installed/signed off up there.

[N2218B]

Steve,
Are you any relation to Charles Inman up on the Hi-line.....Kremlin - Havre area?

[Patrick Phillips]

We put a system on a customers 172 ......he flew it fora couple of weeks testing take off and climb preformance, fuel consumption, speed verse power settings etc.......Anyways after 2 weeks we removed it ....he wasn't happy....Powerflow claims up to 23 percent more power.....the key word here is UP TO 23 percent more....that could mean you only get 2 or 5 or 10 percent more who knows.....my guess is you probably get a few percent more horse power.....not to mention the bottom cowling becomes a bigger job to remove.......you have to remove outside exhaust pipe frist.......... Pat

[GAHorn]

While I don't intend this to be controversial, my own belief is that the Powerflow exhaust claims are a lot of hot air. (Sorry for the pun.)
Think about this: Our engines have fixed pitch props. The sole determination of horsepower output of our engines is tied to RPM. In other words, if you don't turn X amount of RPM you wont' achieve Y amount of horsepower.
The static RPM of our aircraft (with original engine/prop combinations) has a limitation prescribed by the Type Certificate Data Sheet. No other variation is allowed. This means that if the same RPM is realized....then NO INCREASE of horsepower is possible.
In other words, if the rpm didn't increase...the horsepower didn't either.
ON the other hand: If rpm DID increase, then so did fuel burn. And so did heat generated. Yet Powerflow claims increased horsepower with decreased fuel burns and cooler running engines.
Powerflow has miraculously altered the laws of physics.
Save your money (and the looks of your airplane) and buy diet pills instead. You'll get better performance. My 2 cents.

[zero.one.victor]

Member Pete Kuckenberg from St Maries Idaho has a power-flow exhaust on his Lycoming-powered B model. His contact info should be in the membership directory.

Eric

[blueldr]

Good on you, George! There aint no free lunch. There just isn't any way an exhaust system can change the specific fuel consumption of an engine. Unless there is an increase in the static rpm, there is no increase in power.It's just that simple.

[Bruce Fenstermacher]

Ok George I follow your logic but I have this question. Couldn't it be possible for the exhaust to allow the engine to develop higher horsepower at a lower rpm and therefor more HP at 2700. Also remember unless you have a very flat pitch prop you can get 2700 rpm with a stock system. If the Powerflow allows you to reach 2700 rpm only developing 145 hp that would be more than we can usually otherwise develop.

[n3833v]

Take a look at the racing sports. Polish the intakes, polish and streamline the exhaust and you get a better air flow and better mixture for combustion. Hence, more hp, and not necessarly more RPM's.
John

[GAHorn]

Ok George I follow your logic but I have this question. Couldn't it be possible for the exhaust to allow the engine to develop higher horsepower at a lower rpm and therefor more HP at 2700. Also remember unless you have a very flat pitch prop you can (can't ? sic) get 2700 rpm with a stock system. If the Powerflow allows you to reach 2700 rpm only developing 145 hp that would be more than we can usually otherwise develop.

No. Not possible. If the engine is equipped with a fixed pitch prop, and therefore hp is strictly rated as a function of rpm, then any given rpm will equal a certain hp regardless of if it's got a magic exhaust or is painted red or green.
What most people imagine is that the magic exhaust will relieve "backpressure' so well that the engine will "breathe" easier and therefore achieve more horsepower to the prop rather than use hp to pump out exhaust gases thru some sort of restricted factory system. It's a nice imaginative excersize but it's simply not the case. The factory exhaust is quite efficient already. In fact it's documented to be only 2.5 in. Hg at 1.5" from the exhaust flange....it's nothing....hardly a puff of air.

Re: Your second question regarding the ability to achieve 2700 rpm, an rpm which previously was not possible:
Physical Law: If the fixed-pitch prop equipped engine increases hp output it will result in a higher rpm.
So, if such a result was achieved, then yes, the claims would be correct. But the sales claims rely upon the average owner not having access to accurate testing equipment in a controlled environment and not having accurate cockpit instrumentation. How can you know that you've increased rpm over your previous non-modified condition? You practically can't.
BUT...IF you do increase rpm (hp) ...then you MUST increase fuel consumption and heat...by the same law of physics. Powerflow specifically claims that a hp increase will occur while simultaneously reducing fuel consumption and heat. That's not possible.
The bottom line is: In order for you to increase horsepower you MUST increase fuel burn and heat. Powerflow's claims are contrary to that. I'd place more faith in a reduction of backpressure with a simple and short Benham/Bartone exhaust than I would an even longer piping system that makes "pulse" "harmonic" claims. Even more faith I place in my original, even shorter factory tailpipes.


PS- BTW, in the interest of background info: Custom headers are popular among the race-car crowd. This goes back to the days of cast iron headers on OEM units that were improved by custom headers. Heavy cast iron manifold-headers were used by OEM's because they could handle heat and erosion well due to their massiveness and they were cheap to make. When money was available to throw at wringing the maximum advantage out of racing engines, then more expensive alloys could be used to make thin-wall custom, "tuned" headers. The custom header advantge was primarily due to two things: 1-Greater evacuation capability of exhaust gases due to thinner, smooth-walled steed tubing rather than thick, rough/cast-walled iron, (the thin wall steel tubing allowed a larger I.D. exhaust sytem and reduced back pressure quickly to low levels simply due to it's greater volume ), and 2- the thin-walled steel tubes allowed complex bending operations to equal the distance travelled of each cylinder's exhaust which in turn equalized exhaust pressures of all cylinders to an approximately same value. This second factor allowed more accurate fuel metering, especially with fuel injection systems. This had the effect of allowing the engine to be tuned to max power of each cylinder's power stroke (instead of adjoining cyls not having equally high volumes of equal fuel/air mix.)
Airplanes don't have this problem. Each of our cylinders have a short "riser" made of steel tubing which dumps the air into a canister muffler with minimum baffling which might reduce flow. There is no need to equalize the distance travelled of each cyls exhaust because that condition already exists. There also is no heavy-walled iron manifold. We already have short, steel tube "headers" called risers.
Therefore there is no "tuning" of an exhaust available that will influence carburetion in our engines. The entire Powerflow claim, as it applies to our airplanes, is bogus, in my honest opinion.

[N170BP]

In automobile racing applications, the thin walled headers
also weigh considerably less than the stock cast iron
manifolds.

Which leads me to this question: How much weight does this
Powerflow exhaust system add to the airframe? Any (slight?)
hp or static rpm increase would certainly be offset to some
extent by the added weight of the aftermarket exhaust system.

The Rolls Merlins in WW-II fighters had the right idea (no
exhaust system at all, just short stacks to get the exhaust
gases out of the cowling!).

[johneeb]

Bella,

Don't forget those Rolls Merlins had and extensive supercharger systems that would elimnate any need or advantage of a tuned exhaust.

Johneb

[mvivion]

Uh, George, and others, the man's question related to an Avcon converted 170, which in fact, HAS a constant speed prop. He was never addressing the question on a Continental powered airplane, and in fact, Power Flow has never approved an exhaust system for a six cylinder engine.

As to the claims: I asked Paul McBride ex of Lycoming this specific question: If the exhaust increases the horsepower of the engine, won't that invalidate the installation parameters? And, is it possible that this exhaust actually does improve horsepower?

His response: The engines that Lycoming builds are rated and tested in a test cell with straight pipes for exhaust, virtually no back pressure. So, in this configuration, the O-360 is rated at 180 hp. Now, you install it in an airplane, and put an exhaust system on it, plus accessories, etc. It no longer develops 180 hp. The Powerflow exhaust simply makes it more efficient to some degree, and therefore helps to restore some of the power that was lost to accessories and exhaust system.

There is at least one 170 here in Fairbanks with the system, and he likes it. He's had it installed now for several years, and by all accounts has had no big problems.

I doubt if he or anyone else knows whether it gained him 1 % power, or 20 % power, though.

Mike V

[zero.one.victor]

I was talking to a guy who put a powerflow exhaust on his airplane, and he told me he saw a "noticable increase in power". But if I'd just spent about seventeen hundred bucks (?) on a performance mod, I guess I'd probably swear by it too--even if it didn't work.
FWIW, I find those powerflows so butt-ugly I wouldn't put one on my airplane whether it worked or not.

Eric

[GAHorn]

Yep, Mike, I did not miss the fact that the originator of this thread was dealing with a cs prop. (I believe all my comments have emphasized which engine/prop I was addressing. I deliberately limited my previous comments to the original engine and fixed pitch prop in order to keep the example simple, for clarity's sake.)
But regardless of that difference, I still believe the magic exhaust is B.S. If it cannot meet it's claims in a simple engine/prop setup,...a more complicated one will fare no better. (If Lycoming engines make rated hp only without an exhaust system, ...then a magic exhaust is also an installation loss of hp.)
But something had to be lost in the explanation your Lycoming guy gave you. If an engine is rated at a given hp at a given rpm (regardless of whether the prop is cs or fixed),...then if it's operating at that rated rpm it's making that rated horsepower. Minor differences in exhaust pressures do not alter the result. It's the constant speed prop which allows the engine to make rated hp during static and takeoff (because the prop will flatten it's pitch to allow the rpm to be met.) In fact even if....and a big if at that....the exhaust allowed an increase in engine rpm....the cs prop would automatically bring it right back down to the governed rpm. (And I doubt if Lycoming would sell very many engines if their position was that once installed....their engines can't meet specification. )
In fact, a cs prop set up is even less reason to spend money on a magic exhaust, in my opinion. The fact that the prop will flatten to allow the engine to make rated rpm....and the fact that the cs prop will also increase pitch in order to prevent excess rpm....actually guarantees that magic exhaust systems are superfluous. (Even if the magic exhaust claims were true....if it allowed the engine to get more rpm...then that cs prop would automatically roll the rpm right back down by increasing pitch,and the corresponding hp would also decrease. (When the prop and governor are installed one of the very things the installing mechanic is supposed to check is that the system will achieve red-line/rated rpm for take-off but will be governed not to overspeed. In such a case, the best that could be hoped for would be a slight improvement in fuel specifics. Even if those claims were true, I doubt it would ever pay for itself.)
IMHO