Powerflow System

Powerflow System

I was thinking about getting a powerflow exhaust system for my 172N.  Is it everything that I have heard? 

I have also heard that some owners have repitched their props after the installation of this system.  What are the advantages and disadvantages of repitching?

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Re: Powerflow System

Erik,

There has been a large number of posts in the past regarding the powerflow exhaust system.  Do a search on "powerflow" and stand back and see what emerges.

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Re: Powerflow System

I have a powerflow on my 172 K - and I sound like a salesman if I get started.
I increased the pitch of the prop 2 inches and divided the initial 100 rpm static increase to 50 rpm static increase and the other half to cruise. You should check with a prop shop or a couple of them on the specifics as to weather you can repitch at all - they will give you the parameters based on your engine prop combination and your minimum static rpm - with an accurate tach of course.

I wouldn't plan on any fuel savings though - that seams to be sort of an afterthought justification - maybe possible if you throttle back and lean aggressively, but I generally only throttle back when sightseeing. The throttle is pretty far forward for most climb and cruse - thats what I got the system for is more available power, so I rarely discard it.

The mild prop pitch increase does help keep it down from redline a little easier also.     

Lots of the old posts may be mine - I really like the results.
I'd do it again no hesitation.

Ken 

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Re: Powerflow System

What is your change in cruise speeds.  I have a 172K as well.  At 2400 RPM I indicated about 115 statuate miles per hour.  Did you notice much of a change.  Also what about climb rate.

I have the original engine in the plane and it has 1500 TT on the plane.  The engine turns 2350 rpm static.  The prop is the original.  I am wondering the logic of upgrading the exhaust with a high time and old engine.

Ron

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Re: Powerflow System

I was crusing at 2650 rpm and had stated at various times that I was able to maintain 118 kt - I think over a period of time a more realistic maintainable cruise is around 115 kt, however I'm beginning to drop the rpm at 2600 most of the time and that settles in at about 110 kt. the ground speed is where I look for it the most - with A 20 mph plus headwind I still maintain 100 mph or better groundspeed - sorry for the changes in kt and mph but I fly this thing in kt but for some comparisions I use the 100 mph groundspeed as a guide - on the return trip though with a tail wind I've seen groundspeeds at 150 kt - where the gps page is really sliding by.

My 172K has the ram 160 hp conversion, but thats just a takeoff hp range - the 2600 and 2650 rpm are below redline (and full rated hp as long as your at altitude.

My 172K has a nice wing with leading edge mod (bush I think) and wingtips, and gap seals so it handles nice anyway, but with the exhaust it leaves the ground very quickly (about 500 ft) and climbs out beginning at over 1000fpm and keeps 1000 fpm to around 8000 ft msl. - With the family and fully loaded I will usually use 1000 ft of runway and not climb out so agressively so as not to disturb the comfort too much.

The logic of upgrading is that very few things can actually give you more HP at the prop where you really use it. With family, fuel, and luggage on board, on a hot day, you can climb out right to smooth cool air even if its at 8000 ft or go over clouds to 10,000 ft plus, without much hesitation, the comfort zone for the family so they'll enjoy the ride and want to go again - whats the actual useability of your 172 worth?

- and regardless of the engine time your overhaul, cost, and or repair will be  the same because you're only changing the exhaust system - nothing else - everything else remains the same.

one short word on the added hp - I believe that a "correct understanding of the system is that its letting your engine develope more if its full rated hp instead of a lesser value that most engines actually put out - so there is no issue with uver rating or over hp for the engine, just fully developing its full rated power.

I'm going to repeat myself but whats a more fully useable 172 worth (or other AC for that matter) and getting the family of passengers there much more comfortable ??? - all with no other changes to the engine or airframe.

The family got used to the thought that it wouldn't take much more than 500 ft to come or go from almost anywhere - and they like the increased safety margin and that vastly increases your number of "E" fields and that alone gives them more confidence.

- lastly I have held the 172 on the ground during a takeoff roll and a high crosswind, and when I broke ground I was fully confident that I was able to establish and maintain a very positive climb rate - that's nice.

I can go on and on -

0.01
Ken


 

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Re: Powerflow System

...groundspeeds of 150 kt.....

I was flying to southern Inninois from North of Chicago - I had it firewalled on the way there because the direct headwind was 30kt - groundspeed was 90 kt (still over 100 mph). On the way home the direct tailwind was the same so the groundspeed was 150kt (groundspeed was about 170mph) - that was fun.

There are several opinions about maintaining at or near full throttle - and by respected A and P's etc. Since I enjoy My 172 and the available power makes it more useable (especially for specific flights) I use near full throttle sometimes (watching altitude and rpm settimgs so I don't exceed actual power settings - redline etc.)

Some folks advise against the power settings usually for various "wearout" reasons but then go on to add advice to go to a bigger engine installation or a 182, and both of these options are nice but way more expensive, and once you make these changes at least your fuel burn rate, maint and rebuild cost go up and don't come back down.

I really like my 172 and the way it handles. Many times I fly alone or with one passenger (climbout with half tanks and alone or with one passenger is a blast). I've actually had observers tell me to let them know when I'm going to do a max climb because they want to watch.

There are many times I fly much slower and sightsee more and then the cost is very low - either way I think it's a very good, practical aircraft and configuration. Not too much or not to little.

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Ken

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Re: Powerflow System

I do not have a powerflow system, but have considered it when I had to replace my cracked exhaust.

The 4K-5K price tag is a lot when compared to a ~$500 repair, so I passed on it even though it is always nice to have additional power for climb performance.

I have some reservations on increasing horsepower to gain speed in my C172M.  Currently, I fly with a 150 hp Lycoming and always have available horsepower in cruise at 75%.  In fact, I have to slow down to manuevering speed on turbulent days to stay safe.  On those very hot low pressure days, I can stay at 75% and remain at maneuvering speed and still have available horsepower for climbing (although additional power would not hurt when faced with a 500 fpm downdraft).

I see climb performance as the main advantage to increasing horsepower.  Each person values things differently.  Now if you could get an STC to increase gross weight and increase horsepower that's another advantage that shouldn't be overlooked.  My god, you could have a real 4 place airplane!



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Re: Powerflow System

Thanks for all the advice.  Just a couple of extra questions.

Does the Powerflow system increase climb rate at 10,000 plus altitudes? 

Will the pitch change be a good idea for the higher altitudes or should I leave it alone to get the higher RPM's?

The reason I am asking is that my C-172N seems to sometimes have problems holding 12,500 on cold days.  With a service ceiling of 14,200, I would think that the airplane/me would not have to work so hard to keep that alitude.

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Re: Powerflow System

What you get is more hp than you had been producing at the prop. It shows up as increased static rpm or dynamic rpm if you let it rev up -
and I agree that increased climb performance is way up on the top of my list of priorities.

What You do with that hp is up to you - I'm not sure if I had to do it all over again that I'd go through the grief to repitch the prop, and I will recomend that if You do add pitch that you proceed very conservatively and only make slight changes - too much pitch wont let the rpm's wind up and you will not produce as much hp at lower rpm.

The answer to your question about altitude will be what are you experiencing at that altitude - does your max rpm get you what you want or could you really use more rpm at altitude - the later is what I suspect is the case.

If your engine is rated at 150 hp (or whatever) then look at the placcard because its probalbly rated 150 hp at 2700 rpm - or ? So the lower the rpm the lower your engine is actually putting out, and power drops off in a non linear fashion and you loose quite a bit with the top rpm - but you have to look at the power curves to get an idea.


The short answer is that You probably should not repitch and instead trade a little top end airspeed for greater gains in climb especially if you frequent high altitudes.


I really do enjoy my 172 and the exhaust system and it does excellent at gross. Although higher gross stc would be welcome, I really cant complain with what I have.

I would,nt advise going over but I don't have any reservations about filling it up right to gross, largely because climb performance is so good even when it's very hot.

Hope you enjoy yours
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Ken


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Re: Powerflow System

Ken
It looks like I have just put together the same package as yours and looking at  repiching ,or not .
your thoughts on the following rpm's sea level to 2500'
static 2420 (@ max allowed)
climb  2550  80 IAS +/- Red lines (2700+) @ 110 IAS (full power transition to level flight )
level flight 2700 rpm with 75% of throttle used (will produce 2800+ fully opened

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Re: Powerflow System

The 2800+ ...

That's where repitching helped me stay down from redline (under 2700) and still utilize full (or very near full) open throttle.

If You go that way (repitch a couple of inches) I'd advise having your prop dynamic balanced right after - I didn't and I knew better, but I put it off a little and that put a lot of unnecessary wear on My gyros, and they showed it.

2 inch increase will drop about 50 rpm and convert it to cruise and still not use up all that improved climb, but I'm not sure that I would go through the repitch process myself right now.

it's a tough decision.

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Ken

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Re: Powerflow System

Ken
I purchased the prop with repiching included and that includes it dynamic balanced (mainly because your comments in earlier threads). Right now it climbs "really good" and from what you say,I should not loose much on the climb,repiching.The on cruse numbers looks like yours.
THX

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Re: Powerflow System

Great!

Climbout (max) with half tanks and Pilot only is a blast, and when You reach pattern altitude with half the runway left ahead of you it's interesting to hear the comments when you get back.

Ken

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Re: Powerflow System

Ken,

Thanks for all the comprehensive explanation.  You have really cleared the foggy understanding that I previously had regarding what the PF system does for the engine and performance of the airplane.

Do you have any idea how much prop repitching and dynamic balancing of a costs?  Any recommendations on where I should send the prop to get it done?  Also, just to verify, the dynamic balancing is just to balance the prop to eliminate vibration - similar to balancing car tires?

Erik


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Re: Powerflow System

It was in 2001-2002 (I hadn't even realized how lomg its been) and the repitch was about 200 dollars , The balance was about 180 dollars.

Recomendations: the first small prop shop (local) was not helpfull or even interested, I recall them saying something to the effect of  - "You can't just come in here and repitch a prop to whatever you want..."

The next one I went to was Aircraft Propeller Service in Wheeling Illinois on the west side of PWK (Palwaukee - north of Ohare). When I called Aircraft Propellers first they connected me with probably a salesman who in turn put me thru to a tech guy to review my proposed changes. The tech guy looked things up then explained the parameters we had to work under - He needed the engine and prop combination information, then after review, the conclusion was that I would first go recheck my static rpm (into and away from the wind on an almost no wind day - calm would be nice - with an accurate tach, all to make sure that I would be within static limits after the repitch. I did all that then when I brought the prop in (in person) He reviewed the whole thing and we rechecked the book values again. I found these people to be very helpfull and had confidence in them because they didn't take the thing or me lightly, but with research and were professional. The results were very very close to what they had predicted. I would return there without hesitation if I ever need further work. At one time I made a statement which cast some doubt on their "trustworthyness" and the only thing I can say is that I must have misunderstood or misquoted someone, because they were very good to deal with and the results were what they had suggested they would be.

The prop balance was done later after I brought the prop home and had it replaced on my aircraft, eventually I flew it over to ENW (Kenosha) to a small shop (Aviation Plus - Bob Russel) for the balance. I called, set an appointment, flew there then helped out - ran up the engine while Bob did his stuff - when it was done I flew home. The prop is balanced running on the aircraft at normal rpm's, a lot like dynamic balancing a car tire (although for some reason several people don't like comparisons to car or auto anythings).

Some of the delay between repitch and balance was a product of external factors - the mechanic I had remove the prop had gone away in the few days by the time I had brought the prop back, then it was politically incorrect to have an outside mechanic on the field, then my sense of humor faded and I didn't follow up with the balance as soon as I should have - I was happy just to have the prop back on the aircraft.

Small shop or Large - if they are knowledgeable and helpfull and willing to discuss the details with You and do their research -

OK - 0.02

Ken

         

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Re: Powerflow System

I put one on my 150 hp 172M last year.  I also got the fairing mod they offer that goes around the cowl hole the exhaust pipe comes out of:  The original hole is for the wider stock exhaust pipe and the excess gap with the new narrower pipe can allow excess air pressure in the bottom cowl effectively reducing some of the hp gain.  There is a definite improvement in climb with the system, well worth the price.  The plane seems quieter too.  You might also want to consider the ceramic coating they offer for the outside pipe:  It starts to turn brown from the heat otherwise, although I don't mind that because it looks like a cool motorcycle exhaust that way.  I didn't mess with the prop because I usually fly slow-about 2450rpm, anyway.  Climb is the important thing to me and I can now actually comply with some ATC instructions I couldn't before.  Seems like I read somewhere that certain 172 models have a gross weight increase STC available with the Powerflow.

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Re: Powerflow System

I did not see any application for a GO-300 listed.
Besides changing from a GO-300, any hints?

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