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.
Some information that might help you with your decision. Our “ceramic” option is designed only for aesthetics; that is: how nice the visible portion of the tailpipe looks. Except for the last part of the exhaust (the tailpipe) the rest of the exhaust system is made from the same 321 Stainless steel tubing.
Above: Ceramic Coated Short Stack Tailpipe
In fact, ceramic coating the entire exhaust is a bad choice in both the FAA’s view and our view. Ceramic will act an insulator and change the heat profile in the exhaust tube, changing the exhaust’s ability to dissipate heat. However, most critically, the ceramic coating is like a very thick layer of paint. The FAA wants to ensure that you (or your technician) can easily inspect an exhaust tube and be able to see the signs of heat stress or fatigue before it reaches a critical point and leads to a big crack or failure in the tube. With a ceramic coating in place, you cannot easily see signs of impending problems until after they have occurred.
Above: Polished Short Stack Tailpipe
So how did we get FAA approval to ceramic coat part of the exhaust? Lots of persuasion, and the fact that the only part we ceramic coat is the last part of the exhaust that primarily exits the cowling area. In a worse case scenario, if the exhaust were to crack in this area, you would not have a crack inside the cowling that could contribute to a possible safety hazard.
Above: Complete Kit for Cessna 172 with Short Stack Tailpipe
We have not seen any evidence that LOP operations cause damage to PFS exhaust systems, and I haven’t seen that be the case with stock exhausts, either. Excessive vibration is a far greater concern – so get a dynamic balance and check that periodically. As to burn-through; we haven’t seen anything to support or contradict that thought. Ceramic coating acts to protect the base material, but brings with it other issues to be concerned about (above.)
In the end, my advice would be to get the ceramic coated tailpipe option to avoid the look of a brown pipe.
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.
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!