Tuned Exhaust: How it impacts your aircraft engine

A brief primer on tuned exhaust systems.


Muffler

The muffler on the Power Flow system is a different type than the OEM. On an OEM muffler, the exhaust gas enters the muffler where it is diverted by baffles. On the Power Flow system, the muffler is typically an external muffler -- a round can. It is around 3 1/2 inches in diameter and has an insert inside of it. It is a perforated tube. You can shine a flashlight in it and see from one end through to the other without any impediment. As the gases enter this perforated tube, they diffuse into an absorption material behind it. As the gases pass down, they get quieter.

The bottom line

The bottom line is that with a tuned exhaust system, you are always suctioning out and emptying out the cylinder more effectively. So less gas is wasted to overcome the inertia. The engine gets a more complete fuel burn. The effect in the cockpit is that it will take less throttle to get the same rpm than you are used to. This means less fuel flow. The EGT ends up going up a little bit because more of the exhaust gases are being emptied from the cylinder.

System installation

The Power Flow system is installed through an STC. When the kit ships to the customer, they get the most current set plus a copy of the STC and a letter or authorization licensed to the particular aircraft N-number. The kit can be installed by a mechanic in about four hours with little or no modifications to the airframe.

Inspection

So, you see a Power Flow system come into your shop for a 100-hour or annual inspection. What inspection items do you need to be aware of?

To begin with, the inspection would include the items listed in AC 43.13-1B. Inspect to ensure no portion of the exhaust system is being chafed by cowling, engine control cables, or other component. Ignition leads, hoses, fuel lines, and flexible air ducts should be protected from radiation and convection heating by heat shields or adequate clearance. Inspect all external surfaces of the exhaust system for cracks, dents, and missing parts. Pay particular attention to welds, clamps, supports and support attachment lugs, bracing, slip joints, stack flanges, gaskets, flexible couplings, etc. Examine the heel of each bend, areas adjacent to welds, any dented areas, and low spots in the system for thinning and pitting due to internal erosion by combustion products or accumulated moisture. If you suspect a crack, you should pressure test that area to make sure there is no leak.

In addition to the items listed in AC 43.13-1B, there are several other areas Tilman suggests paying attention to when inspecting a Power Flow system. As mentioned earlier, the muffler on the Power Flow system has a removable insert. This insert should be inspected for deterioration and replaced as needed. It can be inspected by looking through it with a flashlight. You can also get an indication of deterioration by inspecting the tailpipe. If the tailpipe starts turning brown somewhere in the middle, and it's shiny on either side, that is an indicator the insert has burned through in that area.

Another wear item is the first-generation heating shrouds. These were made of aluminum and don't tend to hold up as well as the newer stainless-steel shields. This is especially true if the shield has been bumped and lays up against the steel exhaust tube. It can mean a melted aluminum shield.

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