With sport bikes today it seems that performance exhausts are more free flowing than ever before. I know there is a brand called, 'slash cut' or something like that and it is an open header. There were several bikes in AMA last year running straight exhausts, they sounded incrediable. The officials seemed to enjoy the sound, and did not seem to have a problem with the decibels. I do know there are several tracks that watch for open exhausts. Is there a negative in running open exhausts? My concern is more with the engine rather than with the noise. The noise is music to my ears, which I am sure you all undertand. Season's almost here!
I'm sure there's a performance advantage, providing the air/fuel delivery system is tuned to work with it. I image at least some back pressure is needed though. The MotoGP bikes at Laguna last year are the most open pipes I've ever seen/heard, & they sounded incredible. They actually hurt your ears if you were able to get cose to the track. Probably fairly annoying to ride though, not to mention follow.
Every one off our tracks has a noise rule. An open exhaust will cause them to "take notice" of you. Even worse it will cause ME to take notice of you. Frankly, this is the single biggest issue facing our venues and we need to support them. There is a difference netween "tone" and "noise", I don't like noise and neither do the owners/managment of our venues. Monte
What about Jarred's special 4th of july exhaust sounds? I think he was using a exhaust called mortars? . P.S. You guys home yet?
Megaphone exhausts do make more power if the bike is tuned for it. Not worth the extra attention (negative attention) to the sport. Not to mention as Monte said most of the tracks have noise limits. I know Jennings is very strict due to the surrounding area.
Noise pollution is the single most active topic for "locals" in effectively nullifying track use. That is, if you are too loud you will hurt track days. Currently Laguna Seca Mazda Raceway is only permitted to exceed 95 db with 4 events (weekends) each year. MotoGP is one, CART is a second, I believe they'll hold an American LeMan series weekend as a third, and don't recall what the fourth one is, ...so you can see how noise could kill this hobby. The locals in Summit Point, WV are using almost exclusively noise as the rallying point to get other locals active in keeping people away from a fun track. About the word "back pressure", find it in the dictionary, cut it out and through it away. Your exhause doesn't have back pressure, it has "draft" or "flow". A chimney works the same way, too short of a chimney allows smoke to fill the house. The fast moving gases create a draft that helps to pull the following gases along in the exhaust tube. What this effectively does is reduce the pressure in the exhaust port behind the valve. So when the exhaust valve opens the gases that try to leave the cylinder have less work to do (there's less gas in the way blocking the way out). With no exhaust pipe the gases would be fighting atmospheric pressure all the time and be less effective. Open pipes will only help if the "closed" pipe system wasn't designed properly. Do either one right and changing to the other won't help.
Attention I am not good enough to attract any more attention. I will stay quiet and behind the scenes. Much thanks for the responses, JB
We had a guy with a CBR600F4, sans muffler, ride at Summit. I can't begin to explain how annoing it was, you had to stop your conversation in the pits when he went by on the straight. Nice guy, but not very mechanically knowledgable. I believe he thought that if Harley guys do it, then it must add more power to his bike. Needless to say, Marco asked him not to return without a muffler. Plus, if you were to pit next to others, I don't think you'd be very popular. As far as Moto GP, Rossi's bike still has a muffler. I think he's doing pretty good with it. Ad yes, the rest of the bikes were PAINFULL to listen to without ear plugs. Not very enjoyable to watch a race and having to wait tlll it's over to speak.
Rossi said the bike was so loud without a muffler that he couldn't concentrate and it resulted in him going slower.