Hi Guys,
I figured I'd better chime in since it appears I am either cutting half your power, freezing people, or cooking them...:lol: I guess the first thing I should address is the dyno comment. I have always found it funny how you can get so many different results from different guys operating their dyno's. Because of this, I have always thought thrust testing was my most reliable source of information. As you can probably guess, it would not have been possible for me to get this STC if it had in fact caused a deterioration of power. That being said, many engine builders have fun putting thier engines on test stands and then running them way above red line to show some miraculous power achievement. The problem is that it cannot be transferred into thrust efficiently. I have no doubt that under this type of circumstance you can show a power decrease with about any type of exhaust system when comparing it to straight pipes. The fact is, our system is designed to be optimum when running within the engines prescribed limits. If you are running high compression pistons, or are doing some other type of engine modification, it may help to shorten the pipe, or have me build you one with a full three inch tailpipe. However, in normal certified installations, the necked down tailpipe should be optimum. Please keep in mind that it would be easier, and cheaper just to have it built with a full sized, straight tailpipe. We are not necking it down just for fun, or so we can rob you of power...:lol:
As far as the heat goes, this is usually an issue which depends on many variables. Since our entire muffler can is used for cabin heat, there is much more surface area available for heat transfer when compared to the stock system. That being said, I realize that many of you operate in extremely cold climates so I have the "heat ribbon" option which increases heat transfer even more. If you are running the heat ribbon system and you are still cold, it may be hard to get much of an improvement short of lighting the plane on fire... However, I would recommend looking closely at the shroud and ductwork to make sure everything is installed correctly and not leaking. You can do this by hooking up your vacuum cleaner pressure side to the muffler air intake. Then go around and look for leaks, and seal them up accordingly. The guys at Dakota Cub even streamlined the corners of their cabin heat box to increase the flow. (Thanks for the tip Mark:smile
Just keep in mind that it is all about collecting and transferring a limited amount of energy. If you are running a low RPM for hours at a slow speed, you now have less BTU's to capture, and less forced air through the system. Other than using a highly restrictive muffler, which is not an option for obvious reasons, about all you can do is go about reducing the drafts in your cabin. This is usually the biggest area for improvement in Cubs anyway. Keep in mind that this system is used on many four passenger airplanes with much larger cabins, and works perfectly fine without even using the heat ribbons. Therefore it really should be capable of heating the smaller cabin area associated with a Cub. As far as too much heat, I guess we will have to stick with Steves' warning label..:smile: If you have any questions, please feel free to give me a call. Sometimes its pretty hard to cover everything in writing.
Brian Sutton
Professional Pilots inc.
219-696-8726