AVIATION PERFORMANCE PRODUCTS, INC.
MELBOURNE, FLORIDA

The drawbacks of the old cowling designs is that not a whole lot of engineering went into the designs. Fuel was cheap and all you needed was a cowling to direct air to cool the engine in flight and cowl flaps to allow more air through the cowl to help cool the engine on the ground. I chose to use the dual exhaust system from the 260 Comanche, It has been around for a long time and is already approved for the Comanche. A.P.P. Inc. manufactures it out of 331 Stainless Steel instead of the black-iron steel Piper manufactured their system from. The collectors are fitted with slip joints for each cylinder so that they expand and contract with the cylinders helping to eliminate the cracking around the exhaust studs and flanges on the cylinder heads. The most efficient way to get the most performance out of any exhaust system is to keep all the exhaust tubes equal length terminating into one collector, the inside tube diameter the same as the exhaust port, mufflers should be the same on each side and the tailpipes as short as possible. The tailpipes should end where the discoloring of the pipe stops due to the exhaust heat. Any pipe longer than this is to no advantage and can only help build up exhaust back pressure. Without the balance tube there is some after-fireing from the tailpipe on the 4 cylinder engines under rapid power reduction due to the firing order of these engines. After many hours of flight testing I found no negative performance or engine maintenance problems with this system as installed. The best results come from our customers comments that the airplane is noticeably quieter and that the engine performance is definitely improved. So, if your Comanche does not fly at its maximum safe airspeed in cruise flight, the clean up and speed modifications may help you get a little closer to that speed ( which means you have improved the efficiency of the basic design). But you should also know that you may never get to that speed and will probably never exceed it with the given horsepower that is available. Speed modifications or clean up enhancements are not cumulative, so by adding more of them does not make your airplane faster, you can only hope to gain a little improvement from each one (if they even work). the more stuff you hang on your aircraft to go faster the more parasite drag you are also adding to slow you down. There are some reputable company's that manufacture clean up kits, speed modifications and enhancements that improve the design and efficiency of the basic aircraft. You should research each modification and talk to several aircraft owners who have installed them on their aircraft to get information on whether they helped or not.