Category Archives: The Way It’s Done Son!

“Pick Your Price” Discount Program- How It Works

“It looks like Power Flow always has a “special” sale going on! What’s up with that?”

Very observant, Grasshopper, and quite true – we DO!

We call it our “Pick Your Price” program and here’s how it works:

Power Flow can ship a complete Tuned Exhaust System, any version, within two weeks or less. Back in the “Good ole’ (pre-2008) days” we used to sell every system at, or very close to, list price and then spend a lot of time “negotiating” with each Customer to arrive at a mutually acceptable ship date. To meet those ship dates we frequently had to pay a LOT of exorbitant “expedite” fees, overnight shipping charges and overtime rates for our own production team. Not particularly efficient and very stressful on our end because we often had no idea what (if anything) our shop crew would be doing from one week to the next.

When the good times got a little tougher we (along with all the other survivors in this industry) were forced to adapt. We eventually figured out that the further ahead we can plan our production activities, the lower the costs (and stress levels) for those operations become and we are happy to share the resulting savings with those Customers who are also able to plan ahead a little bit.

Our “Pick Your Price” program is designed to do that by offering discounts (usually anywhere from $300.00 to $1,000.00) based on the lead time you select. We review the amount of the discount(s) and the lead time required to get them every couple of weeks and make adjustments based on: #1.) Our current production backlog, and; #2.) How busy (or quiet) the sales phones and e-mailed inquiries have been.

Of course, not everybody has the luxury of waiting, and after some folks decide they want something, they want it right NOW! In those instances, we will drop everything else and focus on getting that particular system out the door ASAP – usually within a week or less, but we charge (and believe me, we earn) full list price for that extra effort.

Although most Customers seem to intuitively grasp the relationship between longer lead times and lower costs, we have had a few enterprising souls call us up wanting to place an order for delivery ASAP, but at the fully discounted price. Their rationale being something like: “Just send me the system that you built for one of those Customers who placed his order 6 – 8 weeks ago.” After congratulating them on their ability to “think outside the box”, I am compelled to point out that we would still be faced with dropping everything else and spending a lot of extra time and money to fabricate and ship a new system to replace the one we ship to them in time to meet the Ship By date we promised to our original Customer.

Another feature that the more perceptive observer might notice is what I refer to as our “Anti-Procrastination Device”. As it turns out, pilots are just as adept at that ubiquitous skill as the rest of the world. So, we give you a good reason to go ahead and take the plunge! It might be a significant discount on one of our optional upgrades, or it might be a limited time reduction in the lead time required to get the biggest discount. Whatever it is, our motivation is the same: we’d like to promote you from Perennial Prospect to Satisfied Customer as soon as possible.

If you can think of a better approach, or even if you can’t but just have an opinion you’d like to share – we’d love to hear from you.

Click here or paste this link in your browser to learn more:


Does the PFS have a flame tube?

This was asked on another user group after a pilot experienced a large loss of power using a traditional exhaust.

In a traditional exhaust, gases are shot at each other and have to diffuse through a flame tube to exit. When that flame tube breaks down, it is hoped that the chunks are small enough to not block the exit from the muffler and thereby causing a potentially dangerous power loss or new hole in the muffler for your air pump (the engine) to relieve the pressure it created.

Example of a stock exhaust system

One of the engineered “improvements” of the Power Flow over traditional Elano style (and other standard) exhaust systems is to allow an uninterrupted pathway for the exhaust gases in the muffler area. For all Exhaust systems except Cessna “short Stack” and our earliest Mooney 200 HP exhaust (PFS-16201 without the quiet pipe), the muffler consists of a 14 inch stainless steel perforated tube that has a 2.0 inch diameter. The gases exit the 4 to 1 collector, go down a 2.0 inch pipe and enter the muffler area and continue down the 2.0 inch inner diameter of the perforated tube. If you look at the PFS muffler, the outer area of the pipe has an expansion from a 2.0 inch area to a 3.5 diameter. On the inside of the muffler, the perforated tube (called a muffler insert) is inside the outer section creating a constant 2.0 inch pathway for the exhaust gas. This is muffler insert is based upon automotive type sound suppression, but adapted for aviation. The inner wrapping that is directly exposed to the exhaust gases is made up of INOX stainless steel fibers, with the outer layer a high density BASALT wrap. It looks a little like fiberglass, but it is brown in color.

Muffler Insert DA40
View looking down installed muffler insert inside tailpipe

Uninstalled muffler insert

This high density wrap around the perforated tube is designed to be sacrificial. It will, over time, break down into very tiny hairs and blow out the tail pipe. The structure of the inner stainless steel tube is designed to stay intact and isn’t standing in the way of the gas pathway. On condition (we have seen between 400 and 800 hours) you remove the entire muffler insert, and replace it with another for about 15-30 minutes labor and $180.00 for the part (pricing correct as of December 2014, subject to change). This can be done in the field, while the exhaust is on the plane, if you want. No overhaul or sending the muffler out for rebuild.

To inspect the PFS muffler, you shine a light up the tailpipe. You are looking to make sure that the inner tube is intact and that you can see the light reflecting back from stainless steel hairs. I recommend that every PFS owner take 10 seconds and do this during pre-flight.

If you have a Cessna Short stack or the earliest 200 HP Mooney Power Flow exhaust, you don’t have a 14 inch muffler insert. The outer diameter of your tailpipe is 3.0 inches instead of 3.5 inches and what you have is a more rudimentary, sound suppressant cone inside the last 5 inches of the tailpipe.

General 472
PFS Short Stack Tailpipe

Installed Muffler Insert

Cessna Short Stack with a Silencer Cone

Because this cone doesn’t have any material on it, there isn’t anything to “wear out.” It is possible that over time the cone will deteriorate and when that happens, it can be easily replaced.


To inspect the PFS muffler, you shine a light up the tailpipe. If you have muffler insert, you are looking to make sure that the inner is intact and not deformed and that you can see the light reflecting back from stainless steel hairs. I recommend that every PFS owner take 10 seconds and do this during pre-flight. If you have a cone type (Cessna short stack and early 200 HP Mooneys), you want to make sure that the muffler cone is still intact.

Darren Tilman
General Manager

Edited 01/08/2015: Previous posting reflected outdated pricing and misstated some technical aspects. We apologize for any confusion.

Why do I have a “popping” sound?

A popping sound is not a normal occurrence with a Power Flow System. The following list should help you troubleshoot the problem:

1. Is there evidence of ‘blow by’ (exhaust leakage) where the tailpipe slides over the 4-to-1 collector or around any of the headers? If so it may be cause.

2. Check the muffler insert located in the tail pipe to be sure there is no partial or complete blockage.

3. Check your induction system for any leaks.

4. Are you leaning as much as the Power Flow will allow on the ground? The Power Flow will enrich the mixture so more aggressive leaning is needed during ground operations.

5. Check the idle mixture on the carburetor by doing a Lycoming idle rise. If it is set too rich it can lead to excess unburned fuel which is ignited by the hot exhaust pipes.



In addition to the above, a leaking primer can cause popping in the exhaust at low power settings. Simply block the line and test fly.

How do you Lean for best power?

Question: I want to evaluate the performance and improvement with a Power Flow exhaust as compared to the Standard exhaust. How do you lean for best power on my fixed pitch aircraft?

Answer: With the throttle at full (wide open), and the mixture initially at full rich, you should start to lean the mixture after passing through 3500 to 5000 feet MSL (reference your POH for specific recommendations).

Leaning gradually you are looking and listening for an increase in RPM. Generally, you should see an increase of at least 20 RPM during a climb from the full rich to peak RPM points. You know you are at the peak when further leaning reduces the RPM from its highest point. Move the mixture back in to achieve that Peak RPM. I recommend releaning every 2500 feet of additional altitude. If workload permits, you could be moving the mixture more often, but then you aren’t looking outside for traffic and that isn’t as safe as flying first, leaning second.

Question: I used the same EGT value for leaning for both the standard exhaust and the Power Flow. Is this ok?

Answer: Leaning of the engine done during the climb to a constant EGT is not as valid as leaning to peak RPM. Peak EGT changes with altitude and atmospherics as well as with the kind of Exhaust system used. It is typical to see a 50-75 degree higher “peak” with a PFS than the stock exhaust. If the stock peak was 1425 at 3500 feet, and you lean 75 rich of that (1350), you may likely be at or very near best power/peak RPM. However, the PFS peak may be 1475 or 1500 degrees at 3500 feet, so leaning to 1350 is actually a great deal cooler/richer – resulting in less than best power and therefore lower performance. This is the problem with the constant EGT method – it doesn’t reliably produce best power. You should lean to achieve the highest RPM, if you are looking for best power.

*Please note, the above pertains to fixed pitch.

Darren Tilman
General Manager

Design Point of the Cessna 172


The following question has been asked recently by a customer who flys a Cessna 172: “…with the D2J, the best fuel efficiency seems to occur near 55% power, say 2350 RPM at 8000 ft. ‘Just wondering what your design point was?”


The answer to this is, the PFS exhaust system for the Cessna 172 was technically optimized at 2450 RPM at sea level. In my flight testing experience, that RPM is the true “peak” point and it is still correct at altitudes as high as 8500 feet. I haven’t specifically tested the Electroair, but I understand how it works and it is the same ignition mapping as the much older LASAR ignition system which I did do some testing on. As the throttle is reduced (actually as the manifold pressure is reduced, but it is the same thing at lower altitudes) the ignition timing will advance as long as it is below 23 inches of manifold pressure. This ignition timing effect may alter the performance and therefore may affect where the peak RPM of the Power Flow is.


Green line represents Power Flow. Notice during over lap, where the exhaust gas valve and intake valve are both open, Power Flow creates a negative pressure to suck out all the exhaust gases.

To figure out what the actual performance curve in your aircraft is for a given altitude (fixed pitch props):

In level flight, set the throttle to 2300 RPM in level flight with it leaned using the same leaning methodology each time. Ie: 50 rich of peak or 75 Rich of peak. Wait 3 minutes for everything to stabilize and record fuel flow, airspeed and engine EGTS and CHTS. Then repeat the test at 2350 RPM, releaning the engine using the same method each time, and after waiting 3 minutes for everything to stabilize, again record fuel flow, airspeed and engine EGTS and CHTS. Add another 50 RPM increment and incrementally go up to 2500 RPM. Then you can look at the data and see at what RPM the best “bang for the buck” occurred. My money is on 2400-2450, but we would love to see your data!

Darren Tilman