Power-Flow Exhaust

Power-Flow Exhaust

OK, someone mentioned the advantages of the Power-Flow tuned exhaust system, and now I'm getting interested.  Anyone else have first hand experience?  I would like some un-embellished comparisons of  "before"  &  "after"  scenarios re. static RPM increase, R.O.C., cruise speeds, cost, etc. 

Anyone out there???

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Re: Power-Flow Exhaust

Search on "Prop size and pitch" and find author Ken Wanagas.  He has some more specifics in that thread.

Have you visited the Power Flow web site?

Balancing the exhaust gasses is nothing new.  It has abeen done with cars since the 1950's to improve hp through improving efficiency (better combustion by scavenging exhaust gasses).  Nevertherless, I found it very expensive; for my C172M is would run ~$3500.  I would probably do it if my exhaust needs replacement, but not before.  I would certainly do it before doing an engine upgrade on a C172.

my $0.02....

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Re: Power-Flow Exhaust

This may offend some,...hope not,...but simple physics dictate that an increase in horsepower will only be achieved by an increase in fuel consumed and heat generated.  If a more efficient exhaust is installed on an airplane in the quest for more horsepower, but no increase if fuel consumption and no increase in engine temps occured,...then no horsepower increase occured either.
Even if hp was increased, it will have negligible effect on cruise speeds because drag increases as the SQUARE of velocity.  That's why higher-hp engine conversions don't improve speed but a few knots, but increase climb rate and shorten takeoff distances somewhat better.

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Re: Power-Flow Exhaust

We have tested some of these exhaust systems and there are some interesting results.  Your comments about FF and HP are basically correct.  On the rich side of Peak EGT, HP is a direct function of mass air flow (MP and RPM) and FF means very little.  On the lean side of peak EGT, HP is ONLY affected by FF.  MP and RPM mean little.

Now to the exhaust issue.  We have noticed that the decreased back pressure in some of these aftermarket exhaust systems alters the F:A ratios to the cylinders!  This has resulted in having to tweak GAMIjectors to regain the balanced F:A ratios that GAMIjector customers have come to enjoy.

A decrease in exhaust backpressure does, in fact, increase HP output, albeit marginal.

Walter Atkinson
Advanced Pilot Seminars
www.advancedpilot.com

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Re: Power-Flow Exhaust

My Powerflow Exaust is on order and should be here in less than 3 weeks, in time to install and test before my flight to Oshkosh.  I already did the 180 HP conversion and now the Powerflow.  I also plan on repitching my prop to put most of the advantage into speed rather than climb as mine already jumps of the runway rather fast.  Talking with the PennYan folks, (the ones hwo did my 180 conversions)  They said that customers who they talked to who did the 180hp conversion and then added the Powerflow, reported that the increase the Powerflow conversion gave them over the 180hp was as big of a jump as the 180hp from the 150hp.

I will do some serious testing before and after and share them here in about 6 weeks.

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Re: Power-Flow Exhaust

   I installed a Powerflow on a customer's 1977 172N w/ O-320H2AD. It picked up about 75-80 RPM in cruise and had a slightly better rate of climb & cruise....maybe 4-5 MPH and 75 or so FPM...nothing scientific about any of this and I don't see how the performance V. cost paid off very well. It's a tuned exhaust system and seems to let the combustion cycle process better, that's all.
  As for marginal performance gains from larger engine conversions...I wouldn't dismiss the gains from the 220HP/constant speed prop with the Franklin. Firewalled in a 1956 172, 4500' MSL, 65 degree day it indicated 154 MPH and showed a sustained 1400FPM climb with full tanks and 400 pounds of pilots on board. 75% power usually yields @145-148MPH. These are observed numbers and prove out on the 170, 172 & 175. The BIG difference is the prop and the HP to spin it. I understand the effects of drag/speed and don't see the benefit of installing a larger engine with only a slightly larger, fixed-pitch prop. Take the 206...much bigger & heavier than a 172 but it still flies considerably faster because of engine/prop. The 185 dwarfs a 170 and flies a LOT faster....again engine/prop. This is really where physics and reality shake hands. My 2 Kopecs worth.

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Re: Power-Flow Exhaust

I stand by what I said.  From a physics standpoint an increase in hp is achieve by more complete combustion.  That is there is an increase in energy being released for the same mass of fuel consumed.  That is, however, only a qualitative statement. 

As to performance, the same limitations and set of forces govern the airplane before the change in hp as it did after.  The engine rating will not increase cruise unless you change the prop geometry.  The amount of work required to turn a prop at a given speed for the same configuration of the plane doesn't depend on the hp rating of the engine.  To take advantage of an increased hp you must create a larger demand which is what you do by changing the prop and increasing.  The increase hp is required to overcome the larger drag as speed increases. 

Horsepower is a measure of rate of work being performed.  An example of work (force over distance), is lifting a weight (airplane) over a vertical distance.  Doing it at a faster rate such as in a climb 800 fpm to 1000 fpm increases the rate at which work is done.  So the added horsepower supports a better climb rate.  But without changing the prop is doesn’t change cruise speed.  So for a gross estimate if you increase the hp to 175 with a powerflow exhaust and your previous climb was 800 you could expect (as a gross estimate) an increase to (175/150 x 800 = ) 933 fpm.  (I say gross estimate because there is no reason that the prop efficiency and aerodynamics should remain the same at different climb rates and I’m neglecting any change in weight caused by the addition of the exhaust.)

What about speed? The drag forces are proportional to speed squared.  Therefore, 110 knots x Square root of (175 hp/150hp) = results in at most an 8% increase to 118 knots with the right change in prop.  So the 4 to 5 knots in the above discussions makes some sense since the prop is designed to increase both speed and climb.

So at the outset, is 4 to 5 knots worth $3500!  We talking 16 to 20 nm further in a 4 hour flight.  (8 to 10 minutes!).  My time in the airplane is not that expensive.  I waste more than that just getting the plane loaded.

Having said all that, these statements are somewhat qualitative  and theoretical.  Reality is what I want to see. I would like see some independent data regarding the results before deciding whether this change would be worth it.

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Re: Power-Flow Exhaust

<<So at the outset, is 4 to 5 knots worth $3500!>>

I, like you, doubt these claims.  Test time.  Who can tell us how many HP it takes to ADD 4-5 knots to the cruise speed?

Whoever gets that answer will likely conclude that the increase of that number of HP is not likely from tuned exhaust.

(hint: it's more than you think!)

Walter Atkinson
www.advancedpilot.com

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Re: Power-Flow Exhaust

Let’s forget about the extra speed and look at the savings in fuel economy for equal speed.  They say 1.2-2.2 gph. savings, OK let’s use the middle 1.7 for my example. With an endurance of 3.5 hours at 115 kts, I get a saving of 5.95 gallons which in turn now pushes my endurance to just over 4.0 hours.  This gives me an additional range of  65 nautical miles.

Yes it will take 824 hour of flight time to recoup my $3500 investment.  But if you look at the total picture of a quieter cockpit, better fuel economy and more speed if you need it, I think it is worth the investment.

I do have a fuel flow computer in my plane and will do before and after testing sharing the numbers here after it is installed.  Hey, if it doesn’t do what they say that it does, they do have a 60 day (after installation) no questions money back guarantee.
.

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Re: Power-Flow Exhaust

OK, let's look at it your way.  A savings of 1.7 gph at the same TAS.  Let's examine how that can be achieved. 

If you are ROP, say at 150dF ROP for argument's sake--pick any MP and RPM you like, and you reduce FF 1.7 gph, you will not change TAS much at all with your current exhaust system as long as you stay ROP.  (maybe a knot)  The HP curve ROP is almost flat.  HP does not change with FF when ROP.  Let's repeat that.  HP does not change with FF when ROP. HP changes with Mass Air Flow when ROP.  That is physics.  Make some SERIOUS measurements *before* you change the system so you can compare apples and apples.

If you are LOP, a reduction of 1.7 gph WILL result in a reduction of  25.33 HP output.  It is not compatible with the laws of physics that you can reduce power output by 25.33 Hp and go the same TAS.

They may have a really good advertising campaign, however.

The only thing that can change by reducing backpressure with tuned exhaust is an increase in MASS AIR FLOW.  Be sure you compare apples and apples!

Walter Atkinson
Advanced Pilot Seminars

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Re: Power-Flow Exhaust

I have some tests in mind to do but if you have some suggestions I'm all ears as I do want to compare apples to apples.  I am a consumer, I want the truth to be known and I want the test I do to be concise.

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Re: Power-Flow Exhaust

I like the powerflow exhaust very, very much.

Like other internal combustion engines the gains ( from the given engine configuration ) are from more efficient use of fuel - I believe you actually get more back pressure, but it's balanced between the cylinders better.

With less backpressure you actually exhaust gasses before they're completely burned and waste that energy - You are pumping out more "wasted heat" - the exhaust system uses some of that waste and converts it into "useable energy" which also is more efficient with the fuel -

if you were tuning an engine for say a race car you would try to dump as much fuel into the cylinders as possible and then exhaust it as soon as soon as the peek hp had been obtained even if you dumped a lot of unburned fuel out - you would be trying to get the next big dump of fuel and fresh air ( oxygen ) in as soon as possible without concerning yourself over the waste of the last amount of fuel burn -

If you were tuning for economy only then you would dump a miserly amount of fuel in and try to keep it in and use it as thouroughly as possible, then go for the new power stroke even if the cylinders had not completely cleared of the old exhaust yet.

Along these lines is alot of "stuff" about valve lift and duration that is very important - but lengthy - stop by your local auto parts or supply shop that has a speed shop within or nearby and ask about "power"  "economy" and how the lift and duration of the valves directly dictate them. 

With a tuned exhaust you can dump a generous amount of fuel in and still use it as efficiently as possible - with no changes to the engine, lift or duration - etc.

As far as payback time - I don't think that would be a reason for the exhaust - maybe an afterthought or justification, but I doubt a real reason. I actually use the same or more fuel sometime when I have kept it firewalled, but then I'm getting a lot more use without the expense of going to a bigger, faster .....Lots and Lots more expensive than the exhaust system.

You do get more available power, however you choose to apply it.

I split mine between climbout and cruise and climb. About 50 RPM static (and of course climb) and the other 50 or so RPM went to adding 2 more inches of pitch to the prop - slightly higher cruise but it's easier to maintain a reasonable speed when you're finishing a shallow climb in hot air.

The justification for my installation was that it gets the family and full fuel airborne quickly, is easy ( and quicker ) to climb out to cooler smoother air, and cruise is slightly better. Even at gross weight climbout is good on a hot day - an additional safety factor, and is quieter both for the passengers and the people on the ground, and I'm always arriving or climbing out of some place where there are "noise" proceedures - quiter is better. 

This puts the whole family in a better mood and they're more enthused about gettin back in the airplane next time - and I have had experiences in the past in other planes where they were a little reluctant to fly again.

I have a nice stoll wing and with the added climb of the exhaust system it seems as though we would be able to come and go in an emergency in minimal ground contact - seems to add a safety factor and the comfort that we could get in and out of many more tight places - if it was a necessity ( The E word ) and the family likes that also.

I like it and the Family enjoys the 172 more - what's that worth - like justifying the cost of the aircraft in the first place - what's the convenience and fun worth - it changes over time and with your own priorities - but the return on the cost of the exhaust system is real and large compared to what you get of many other mods or new radios - I don't know how to quantify a new GPS sometimes - but sometimes I'd rather upgrade than not.

0.02 ----- maybe more

Ken Wanagas

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Re: Power-Flow Exhaust

Wow--I never dreamed this topic would stir up so much "opinion". 

Well, as Barry said earlier, "I would like to see some independent data regarding the results before deciding whether this change would be worth it."   
Key word here is "independent"---I wonder if someone who already paid $3500 for one can be as objective as an "independent" tester.  Still, I am anxiously awaiting the results from Curt's installation.  Curt, please keep us in the loop--thanks!

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Re: Power-Flow Exhaust

The truth will probably be found in the seller's disclaimer statement. ;Þ
I have a new product I'm selling called "Superslick".  It's a special formulation of H2O that, when used according to instructions, will change the coefficient of friction on the aircraft surface after washing.  It makes the airplane lighter, faster, and reduces fuel consumption and aerodynamic drag.  It has a life-time, money-back guarantee.
Send $19.95, plus $9 freight, shipping and handling to :
Superslick, P. O. Box 41, Spicewood, TX 78669
Receive a discount two-for-one if you respond in the next 20 minutes.

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Re: Power-Flow Exhaust

George, Do you take  Paypal ? He he.

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Re: Power-Flow Exhaust

Curt,

You wanted to test apples and apples so to do that you need to do some "before" and "after" testing and understand the data you collect.  After referring to Mark’s Handbook for Mechanical Engineers (10th Edition), here are some thoughts and information.  Also, based on George Horns’s and Walter Atkinson’s experiences or others for that matter, perhaps they can add or improve the ideas on the engine and flight tests.

To do this testing you need to make changes one at a time, if practical.  If not you will confound the results.  If you add the Power Flow Exhaust, change your prop, replace your air filter, clean-up your spark plugs, change your oil, adjust the carburetor and change any aerodynamics characteristics of the plane your will be hard pressed to make a very accurate assessment.  The power flow exhaust adds weight and part of it is in the flow stream.  You are also removing your old exhaust from the flow stream.  You can compensate a little by adding the weight difference in the front seat during your “before modification” testing.  You can’t do much about the effect of the difference in the center of gravity shift nor the flow stream effect, but we’ll just have to accept that when mulling over the flight test results.  However, we live in the real world with limited resources, so I suggest making as many of the changes you decided on before you do the initial “before” testing and before the switch in exhaust systems.  The best way to test the engine is in a laboratory, but that would be expensive.  So static operation without flight appears to me to be best we have as a cheap lab.  Remove the flight characteristics from the equation.  Nevertheless, flight performance is what you and all of us are interested in so in the end, you will also want to do the flight tests (“proof in the pudding” tests).

If you are going to change your prop at the same time to achieve an optimize speed and climb performance, you probably can get performance information about the new prop regarding required brake horsepower (HP) versus static rpm.  If you use the old prop, we’ll just have to accept the differences between a used and new prop.  But in both cases, you still need manufactures charts to determine the required HP to turn there prop at rated engine speed.  There chart may also correct for differences in atmospheric conditions for the prop.   For the engine, brake horsepower can be correct to a standard using the following formula or charts from the manufacturer:

For a spark ignited engines (Otto cycle) -

HPs = HPo (Ps/Po) x Sqrt(To/Ts)

where:
P is dry barometric pressure and
T is absolute temperature e.g. absolute T, degrees Rankine = degrees F + 459.69 (460 is good enough for our little experiment with your airplane)
o represents test conditions (observed at the time you are doing whatever test you are doing)
s represents standard conditions the Powerflow Exhaust manufacturer believes you will achieve their performance claims.

Calibrated instruments are standard before testing, but with limited resources we must do without or just recognize the limitations in the results.  We are interested in changes so we should observe and focus on changes rather than absolute numbers.  That will minimize calibration errors.  It would really be helpful (perhaps essential) to have an accurate measure of rpm.  So check with your mechanic, he can help.  If you have a True Prop or other electronic tachometer we’re in business.

Engine Test:
During the full power static run-up, lean the mixture for peak rpm performance.  After all, we are interested in maximum full power performance.  Make sure the engine has achieved a steady state temperature.  Someone else may have an idea about this, but I would guess at least 5 to 10 minutes.  I’ve never done that long a static run before, is it safe?  Are there any warnings by the engine or prop manufacturer? 

Record the following:
rpm
fuel flow,
Outside air temperature,
dewpoint,
Atmospheric pressure,
All Engine information available e.g. CHT, EGT
oil temperature.
Others? (Cylinder pressure would be ideal, but we’re dreaming)


Flight Tests: 
For your flight test keep track of barometric pressure and outside air temperature, (Density Altitude), indicated airspeed, aircraft weight and center of gravity.  For climbs keep indicated air speed the same and keep track of ambient temperatures before, at some mid point, and after the climb and use a stop watch to record the times.  Start with full tanks and go through the same routine before testing and after. 
Do each test a number of times at least three (the more the better).  Make remarks about the factors you observe that might affect your results.

1) Rate of climb at say 90 mph indicated.
2) If you have a new prop for speed, TAS at three altitudes say 8500, 9500 and 10,500 at 2700 rpms.
3) Maximum altitude that you can achieve a 100 fpm climb.

Back to the debate…..

The equation for HP in a spark ignited engine is:

HP = Pmep x S x A x rpm /K
Pmep is mean effective pressure
S is stroke
A is area
rpm well you know
K is a constant

I purposely left off units because I don’t envision you recording cylinder pressures during the engine run.  However, this formula is instructive in the debate about whether we should see a difference with a tuned exhaust.  So anything you can do to raise the mean effective pressure at any RPM will increase HP.

One way to increase Pmep is increase the cylinder charge, i.e. the amount of fuel (keeping the fuel to air ratio constant) that is drawn into the engine on the suction (intake) stroke.  How can “tuning” the exhausts backpressure help?  Here’s my guess.  Well if you improve the volumetric efficiency of the engine you will add charge.  This will raise Pmep and improve HP.  This is what George is saying when you add additional fuel to get higher horsepower.  To improve volumetric efficiency you need to reduce resistance to air flow both on the intake and the exhaust.  Other factors that add resistance to flow is higher cylinder temperatures as higher temperatures change the properties of the gases.  (Volumetric efficiency is the actual volume of air fuel mixture drawn into the engine divided by the piston displacement.)

The other side of this is to remove as much of the combustion products from the engine so you can add more charge and get a better more complete burn.  However, I would only be guessing at the whether this is important.  According to Marks handbook for Mechanical Engineers, the blowdown phase of the exhaust removes about 80% of the exhaust gasses.  15% is pushed out of the cylinder by the piston (pumping work) and the remainder is left in the clearance space.  The blowdow phase, which I would assume is governed by pressure difference between the cylinder and the exhaust just downstream of the exhaust port.  This pressure difference is the primary driving force that exhausts the gasses..  Since pressure is high in the cylinder you have choked flow for much of the blowdown, but as pressure reduces below critical pressure ratio the lower back pressure should help thereby removing more gas and requiring less pumping work and improving volumetric efficiency.  That is with less gas in the cylinder at at the start of the suction stroke, a higher vacuum is produced drawing in more fuel-air mixture.


Got to get a life….

my 2 cents…

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Re: Power-Flow Exhaust

Barry:

WOW!  An excellent explanation of how hard it is to get good data!  And, what needs to be considered.  Nice job.

Two things left out:

1) The powerflow exhausts alter the F:A ratios in ways completely unexpected.  We have significant data on this from the test stand as well as in-flight measurements.  This is not insignificant and is not good.  The makers are unaware of these effects and in one case, disregarded the measured data because it didn't tell them what they expected.

2) The Pmep formulas you mentioned will help determine output, but the most important numbers to know are the internal cylinder pressures and at what point they are occuring in the cycle.  As far as I know, the only place in the world where these can be measured in real time is at the Carl Goulet Memorial Engine Test Facility at GAMI in Ada, OK.  Soon, we will be able to measure these pressures in flight.

The real point here is that the effects are hard to measure and sometimes harder to understand.  We see things happening here that no one expected and no one measured, including the makers of the system.

Walter Atkinson
Advanced Pilot Seminars

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Re: Power-Flow Exhaust

OK if there is significant  differences in the fuel-air ratio - especially if is appears not good - please share some insight with us ? !

?

Ken Wanagas

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Re: Power-Flow Exhaust

Ken,

It sounds like you are taking this personal.  I believe that you are getting good value out of your PowerFlow Exhaust.  You have indeed experienced a better climb rate and increased speed, better disposition and your family enjoys flying more.  Obviously, something good is going on. 

I would not be surprised that the F:A ratio is not predictable, though.  According to Mark’s Handbook, determining F:A ratios in carburetors has always been unpredictable.  So I also believe Walt about them finding unexpected F:A. 

Considering the various phenomena involved in carburetors, F:A ratios would be very hard to predict, that is either calculated or using empirical data to extrapolate.  I also learned that with full throttle not all fuel is vaporized by the time it reaches your cylinder.  So increasing the airflow may mean things might get worse in this regard.  My conclusion is just a guess.

So that is why I suggested to Curt the testing in my last post. Even though we may not be too accurate, we should see a difference.  A 16% increase in Horsepower (175 HP versus 150 HP) should be noticeable.

Note:  A static run will not get you to the engines design point because you cannot develop full RPM.  Nevertheless, you should see a noticeable difference, before and after.  At least, enough to get an estimate of the change.

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Re: Power-Flow Exhaust

I wonder if I have missed something in all this?  My understanding of the powerflow exhaust is not that it will increase hp over and above the 150 of the O-320, but rather only permits the O-320 to develop hp that is closer to its rated hp.  that is, after installation, hp developed will be closer to 150 whereas before the engine was only putting out about 130 to 135.  The only way to generate more hp would be to turn the crank faster, ala the go-300.

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Re: Power-Flow Exhaust

You are more correct.  Here's what I found on their website under testing:

"Here is what we found:

Peak Horsepower Developed:

PFS Tuned Exhaust:157.1hp

OEM Cessna exhaust:133.3hp

That's a 23.8hp difference! Those extra horses really give you a dramatic pitch angle on Vx and Vy climbs. It is by far, the most impressive difference you will notice on your first flight after installation."

This represents an ~18% increase.  It should be noticeable!

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Re: Power-Flow Exhaust

I guess I am taking this to heart, I do like the powerflow exhaust system and I believe it's an improvement over the non powerflow exhaust, but even if I believe it to be good, When a statement is made about it being not insignifigant and not good, based on apparent data they are aware of - I really do need to question it, and even if I like the exhaust - if there is specific data somewhere that could tell me otherwise I would like to evaluate it or be at least aware of "not good" even if it means re-evaluating my perception of this exhaust system. I don't want to blindly trust this system if there is real data out there to the contrary.     

Thanks

Ken Wanagas

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Re: Power-Flow Exhaust

Ken,

You raise a valid point.  If you "not good" is "bad" and not just benign.  If something potentially seriously bad e.g. like causing engine failure or shorten engine life, I would believe this would impose a moral and possibly a legal obligation to identify this to you, the manufacturer, and to the FAA? 

Walt stated:
"1) The powerflow exhausts alter the F:A ratios in ways completely unexpected. We have significant data on this from the test stand as well as in-flight measurements. This is not insignificant and is not good. The makers are unaware of these effects and in one case, disregarded the measured data because it didn't tell them what they expected."

We also should recognize that "Not good" could mean not really more efficient or maybe worsen efficiency.  That would be much less serious. I would think after installing a new system it would be the pilot/owner's responsibility to validate fuel consumption rates after the installation.  What are the post modification test requirements on STC'd items?

On the other hand, since engine horsepower is increased without any other modification, wouldn't this put additional stress on the engine over and above the OEM?  OK, an 18% increase doesn't sound that much but it should have been investigated.  Wouldn't the maker of the Powerflow Exhaust have to demonstrate to the FAA that there would not be any adverse effect on engine life due to the higher pressures in the engine cylinders?  My guess is they would have. As a owner, who could or should I trust? 

2 more cents worth

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Re: Power-Flow Exhaust

I just got a system installed on my 1972 - 172N with Penn Yann 180HP engine.  It have a good boost to climb.  I am not much of a mechanic, but the engine seems to run smoother in cruise.  Plus I can run it at 2450 RPMs and get 120-124 kts. 

I know a few people who have installed them and have needed to re-pitch the prop or replace it.  Re-pitching mine would probably give me a few knots. 

Eric Garrison

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Re: Power-Flow Exhaust

And what about the increased drag caused by all that Powerflow exhaust system hanging out there in the breeze?  No penalty there? 
Simple physics and logic dictate that an increase in hp will only occur if an increase of fuel/air is consumed.   If the Powerflow system allows the engine to breathe easier,....then it only allowed the engine to suck in more gas/air.  The engine is rated at a specified hp at a specified power setting (either rpm with a fixed pitch, or m.p./rpm with a c.s.)  If, in the interests of accurate comparison, you cruise your engine before the conversion at  a specified power-setting that is IDENTICAL to the after-conversion power-setting, then you are producing EXACTLY the same hp.  The only question to be settled after that $3500 modification is "how much drag has the $3500 expenditure added to my airplane,...and how much more hp must I develop to overcome it?"
  The only other alternative is the elusive possibility that less throttle is required to achieve the same hp as before the conversion,...in which case all you have to do is overcome the increased drag by adding additional throttle...which eats into all that efficiency those 3500 dollars supposedly purchased.
  I personally wouldn't give you 2 extra cents for your airplane when you later tried to sell it to me, ...in fact... I'd make you discount the airplane's value the necessary amount required to re-install a factory new exhaust system to restore it to original configuration.

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