First off, this is by far the best snowmobile magazine. My question is about stock pipe(s) vs. after market pipe(s) running temps. Most stock pipes come with an aluminum shield and a bit of insulation between them. Is this for reducing sound or for keeping a pipe hot? Next question is when people put twin pipes (or an after market single) on their sled, would it benefit to close any air duct’s leading directly to the front of the pipe(s) to keep them hotter? I have experienced how a snow drift hits hot pipes and the sled bog’s down, is this from too much moisture/steam getting to the carbs or the heat reduction of the pipe(s)? Are ceramic coatings worth it? Can you explain any of the pluses or minuses of exhaust systems?
Grand Rapids, Michigan
There is enough information on what you’re asking to fill a couple of magazines, and much of this has been covered in tech articles over the years in SnowTech Magazine. Check our article archives on-line as many of these tech features are now posted for reference, and all should still be available in our back-issue library that you can order from as well.
As for the heat shield on stock exhaust systems, they are there to do both; reduce the noise emissions (shell noise vibrations) emanating from the surface of the exhaust pipe, and to provide a quicker warm-up and stable pipe temperature. A two-stroke tuned exhaust pipe makes it’s power at a specific RPM, but this is at a SPECIFIC temperature. The exact RPM at which your engine makes its power is very dependent on the temperature of the pipe and the gasses inside. Without having to re-write the articles about the speed of sound, let’s just say that a pipe that reaches ideal operating temperature and stays there is best matched to the clutching system, which is calibrated to this operating RPM.
This is why recent year snocross sleds incorporate an ignition timing retard at the starting line, as this gets the pipe hotter faster, so when the green flag drops the pipe is as close to ideal temp as possible, so the engine makes as much power as possible and the clutching calibration is matched as well.
Are there benefits to closing off forward facing air ducts? Possibly, but this would likely lead to other heat related problems that would be more of an issue. Like, the overall underhood temperatures, clutch temperatures, and all parts and pieces close to the exhaust system. For short runs, the lack of cooling airflow across the pipe could be beneficial, but generally for mainstream use you want to keep the underhood cavity cooler, not hotter. When you hit a snow drift and the snow hits the pipe, the sled is bogging more due to the drop in exhaust system operating temperature than anything else. This also can crack some of the thinner wall exhaust pipes.
Ceramic coatings? They’re good for several reasons; they look better due to the anti-corrosion nature, the pipe tends to only discolor instead of rusting. The ceramic coating also keeps the heat inside the pipe instead of radiating out and away, so the pipe typically heats up faster and operates at a stable temperature more often. Some tuners actually report the ceramic coating change the operating RPM slightly, raising it 100 RPM or so. This would be due to the heat retention and higher operating temperature. Some riders will remove the aluminum clamshell material and the insulation from their stock pipe, only to find corrosion has started due to the moisture retention of the insulating material. Ceramic coating the pipe in this case pretty much eliminates the need for the insulation, but does little for the shell noise reduction of the exhaust (minimal, but a consideration). You might notice a slight more â€œtingyâ€ or â€œding-dingâ€, more subtle than anything. Generally, ceramic coating is a good thing for the durability, appearance and operating consistency of the exhaust system.
Bottom line, start with the recommendations and suggestions of the supplier of the exhaust system. Each exhaust system is designed to operate at a very specific operating RPM, and this means a very specific operating temperature. This is also why some exhaust systems work well on the dyno, but not so good in the field. The reason? Differences in pipe temperature between the two environments. There is so much more to this subject, this is only a teaser of a response.