Jump to content

To Powerflow or not to Powerflow - That is the question


Bart Chilcott

Recommended Posts

We have 30 some 172's at the flight school I worked at. One p model had a pf exhaust. The difference in climb was significant. I owned an e and installed the bracket air filter (challenger, k&n?) that added about 3/4 of an inch of map. If I owned a c today I wouldn't hesitate in insalling the stc'd air filter and pf exaust, especially if I planned to keep the plane for many years. If it's just a time builder or you've got your eye on a nice 252 or ovation in a few years then I'd go the cb route and have the old one rebuilt. I got a nice rebuilt for about 1400 or so but that was quite some time ago. Dmax is a very practical, old school guy and doesn't seem to do change well. Least not when I was dealing with him:) He still arguing against lop ops? :)

Link to comment
Share on other sites

2 hours ago, Petehdgs said:

After reading this thread it appears to me that some of you may not fully understand what an exhaust header is supposed to do and why.  

What I was wondering...

1) does the PFM work as advertised on the Mooneys, or not? (So many details beyond the theory...)

2) Do I need to fully understand what an exhaust header is supposed to do? Or why it does it?

3) Let’s assume for a moment, I understand the thermodynamics of internal combustion engines used in my Mooney...

4) There are quite a few MSer’s that will be reading this thread.... Let’s assume for the moment, they don’t feel insulted when they are told they may not fully understand...

5) If we have the required AMUs, and want to spend them... will we see the performance improvements or are they fictional creative writing exercises by the PFM marketing team, foisted upon the unknowing aviators..?

6) Often, The PFM is being considered as a replacement for the original hardware... and comparisons are being considered... fit, finish, maintenance issues, does the heat still work... all important issues...

7) If the PFM works so well at removing exhaust gasses, because of its brilliant design...does the exhaust expand so quickly under low atmospheric pressure, that the EGT becomes colder, and residence time is minimized....does the EGT drop too fast to allow adequate heat transfer to occur..?

What say you, Mr. Hodges? :)

Note: To keep an eye on my fuel level... I use a flow meter and totalizer, backed up with fuel level gauges, and another set of fuel level gauges for another level of back-up...

What brings you to visit MS? Looking for a faster, more efficient bird?

Welcome aboard, and best regards,

-a-

Link to comment
Share on other sites

>>> Welcome aboard, and best regards, >>> Thank, you Carusoam

>>>What brings you to visit MS? Looking for a faster, more efficient bird?>>>
I initially joined when I was looking for a better bird.  I owned a '68 Cherokee 140 from 6/04 to 12/17 13.5 years.  It took about 6 months without my own bird to realize I really needed my own bird again.  So I started looking and comparing models and based on the flying I do, and want to do in the future.  That includes some grass field work and possibly mountain flying for a trip to Utah or Alaska or Canada.  I sought out and bought a '64 E model about 6 months ago in part because it is the best short field Mooney and in part because it can be reasonably priced to purchase, own, and maintain.   My bird a really nice example of the type and is basically a legacy aircraft with some speed mods.  The fact that it is all mechanical with steam gauges suits me perfectly.  I love it.  I had forgotten that I signed up here until I started researching the PFE exhaust system for my bird. 

>>>Note: To keep an eye on my fuel level... I use a flow meter and totalizer, backed up with fuel level gauges, and another set of fuel level gauges for another level of back-up...>>>

Right now I do not own a fuel flow meter and have not owned one.  I understand their usefulness, especially in airplane operations, but I am frugal and can get the same information through other means.  I am not saying I wouldn't spend the money to buy one in the future, but it is not high on my list because of cost vs benefit to me. 

>>>>>1) does the PFM work as advertised on the Mooneys, or not? (So many details beyond the theory...) >>>
I can't say from personal experience at this time, but they have published data that can be duplicated in the field, and their claims are not unreasonable.  I would say that they are likely to perform as advertised and they have a 60 day return policy (parts only no labor) to back it up.  As long as you understand the gains are small, and not likely to pay for themselves in fuel savings alone then my short answer is yes. 

>>> 2) Do I need to fully understand what an exhaust header is supposed to do? Or why it does it? >>>
Yes and no.  Airplane ownership and maintenance involves making informed decisions as to how best to spend your hard earned money on your own airplane.  Most people don't know too much about exhaust systems and that is normal.  Years ago I read an article in HotRod that asked the simple question: If I buy this muffler for $40 or that muffler for $90 what do I get for my extra 50 bucks?  That sounds a lot like the same questions raised here in this topic.  HotRod based an article on that question and used a chassis dyno to power test 6 different mufflers that were popular at the time.  That is the first article that introduced me to the complexities of exhaust systems.  Do you need to know all that to maintain your airplane? No.  Do you need a good working understanding of what you are buying or not buying if you are considering new equipment for your airplane?  I say YES.  If you have to replace your exhaust anyway, then the labor part of the cost is the same.  If a new stock system is $2000 and a new PFE is $4000, you are going to spend $2000 anyway (or $1800 or $1500 depending on cost at the time).  That means the upgrade is really only $2000 instead of $4000 because you would have spent $2000 anyway.  But the PFE is supposed to be the last exhaust you will need to buy.  It all boils down to personal choice and cost vs benefit, and to make an informed decision you need to know what you are buying or not buying. 

>>>3) Let’s assume for a moment, I understand the thermodynamics of internal combustion engines used in my Mooney... >>>
>>>4) There are quite a few MSer’s that will be reading this thread.... Let’s assume for the moment, they don’t feel insulted when they are told they may not fully understand... >>> Not an insult, just an observation based on the contents of the posts.  There is no shame in not knowing everything in aviation.  No one person can know it all, least of all me. 

>>>5) If we have the required AMUs, and want to spend them... will we see the performance improvements or are they fictional creative writing exercises by the PFM marketing team, foisted upon the unknowing aviators..? >>>
I am not sure what an AMU is.  The rest of the question is a legitimate concern.  Do they work or are they trying to blow smoke up your A##?  Even if their claims are true, the improvements are very small and may not be readily apparent to some owners and pilots.  Want to climb better?  Simply fly on cooler days!  If you test the stock system in 40F weather and test the PFE in 60F weather you may not notice anything at all.  That is because the gains are small enough that a change in weather on the testing days may make the improvements appear to vanish.  In the industrial engine business engine performance is guaranteed at at a certain air temperature and altitude.  Hotter today?  Not as much power is produced.  Colder today?  I've got me a little hot rod.  I truthfully can't tell you the performance improvement claims are real.  I can tell you they did their best to provide data that can be repeated.  That alone should say they are real... but small. 

>>>6) Often, The PFM is being considered as a replacement for the original hardware... and comparisons are being considered... fit, finish, maintenance issues, does the heat still work... all important issues... >>> I agree

>>>7) If the PFM works so well at removing exhaust gasses, because of its brilliant design...does the exhaust expand so quickly under low atmospheric pressure, that the EGT becomes colder, and residence time is minimized....does the EGT drop too fast to allow adequate heat transfer to occur..? >>> The working fluid in an internal combustion engine is air in its various forms.  Air, Air and Fuel,  Air and Fuel on FIRE, and Air as spent HOT exhaust gasses.   Air and fuel has mass, and connot be stopped or started instantaneously.  The work that is being done here is to use the energy in the exhaust during the valve overlap period to help start the flow of intake air into the cylinder as the intake valve opens, before the movement of the piston is actively pulling the air in, thus displacing the remaining exhaust gasses into the exhaust system.  This is where the timing of the exhaust pulses causes a suction on top of the piston to help pull the intake air into the cylinder as the intake valve just opens.  The suction pulls more of the spent gasses out due to lower pressure near TDC, and the lower pressure helps suck out the intake air, which is stationary next to the valve, at the instant it begins to open.  Once the intake charge is moving and the exhaust valve closes that work is done.  The reduction in EGT is mostly a result of less preheating of the intake air fuel charge on top of the piston because less of the hot exhaust gasses are present.  The increase in power comes from more overall air and fuel entering the cylinder, thus increasing volumetric efficiency.  My previous calculations were 8% more power (more air), and 1.56% better efficiency (less fuel burned at the same power output). 

I hope that answers most of your questions.  I am out of time right now. 

 

Edited by Petehdgs
  • Like 1
Link to comment
Share on other sites

I wonder how much of the benefit is due to the tailpipe extending into undisturbed airflow? (Same reason the P-51 intake scoop is not flush with the belly). Maybe more suction or less back pressure with that design? Dunno, just askin’.

Skip

Link to comment
Share on other sites

I installed a PF on a 180hp floatplane where we really needed the extra 100rpm it would provide on the slide.  I did not care for the extra noise it makes or for the extra annual expenses.

At one stage I had an extra PF exhaust, and I think PF wanted $300 or 500 to transfer the STC. Too high in my opinion, sometimes things change and you have to move a product from one plane to another.  They also play ridiculous games with pricing and delivery schedules.  This is not an airline ticket where you need to pay a premium for delivery next week.  For these reasons alone, I probably will not install another one.

 

Aerodon

 

Link to comment
Share on other sites

Nice additional details, Pete!

Need some proof that an M20E makes an excellent retirement plane? :)

Best regards,

-a-

 

Hey Pete @Petehdgs, look below, an awesome example of an MSer’s M20E with a PFM just flew in... :)

Bob has built a great example of what is often called a forever plane...

Link to comment
Share on other sites

Thanks for the kind words. 

Bob, what kind of cowling is on the front of your bird?  It looks similar to stock but with smaller air inlet holes.  Can it be added without much fuss? Or is it a 70 hour install?  Does it improve airspeed or climb?  You have my attention!  

Just so you all know I'm not much on cruising through message boards except when they show up in searches about things I am curious about.  If you come across something that you think I might interest me give me a shout.  I might not answer right away but if it is interesting I'll be sure to take a look.  

Edited by Petehdgs
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.