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Both really good articles but let me ask you this:

If a set header/muffler combo is designed to allow a perfect combination of velocity and adequate size for a given engines power-band, and you remove the latter half of the exhaust system, would you not lower the design velocity and thus loose some of the torque created by said velocity.

If you look at a normal exhaust system, the muffler usually has the most restriction, which causes an increase in velocity due to a smaller flow area. This is where the backpressure issue come into effect. It is not really the backpressure that gives torque, but rather the increase in velocity caused by a smaller flow area.

Correct me if I'm wrong, I'm just trying to make sure I understand.
 

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all of the arguments and facts are good points.. but i have done alot of dyno runs (mostly cars but still has same theory's) and depending on combo you need some back pressure for best torque levels.. now probably on a bike really wont matter considering the main torque is needed in the lower RPM band and the bike is running best at 10K plus.. but for a car it is pretty optimal unless you are running some serious HP.. i did like the topics at hand, finally a good thread worth reading..LOL..
 

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BACKPRESSURE IS A MYTH.......

Your referring to exhaust flow, which is the correct term.

Too little exhaust flow, and you lose power, to much and you also loose power..........


Its all relative to the length of the exhaust, and in some parts..diameter.
 

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BACKPRESSURE IS A MYTH.......

Your referring to exhaust flow, which is the correct term.

Too little exhaust flow, and you lose power, to much and you also loose power..........


Its all relative to the length of the exhaust, and in some parts..diameter.

Exhaust length is important because of pulsation control. As an exhaust pulse travels down the pipe, it must maintain a certain volume (or shape) in order to effectly offer scavenging for the following pulse. This explains why longer tubes are needed to offer proper scavenging at lower rpms. Because pulsation is happening less frequently, a given pulse needs to stay in the tube longer than if the pulsation were happening more frequently. Diameter does become an issue because along with a given length, a smaller tube will increase velocity and could cause a pulse to leave the exhaust system at an earlier time than if the tube was larger. Right?
 

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tee, you're under the mistaken impression that scavenging relies on backpressure, it does not. the more backpressure you have the more burned fuel stays in the cylinder. the more burned fuel that stays in the cylinder the less new fuel/air goes in. Enlighten me as to how this is a good thing.
I'm saying the pulse frequency of the exhaust gasses are dependent on several variables including backpressure. The effect of increased backpressure is that it reduces the effective length of the headers, generally.

Again, this is only true with a tuned exhaust system. The exhaust on your F 150 or your Nissan Maxima has no scavenging capability. For a typical production car or truck, less restriction = more torque and horsepower through the RPM range.
 

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Yep I ran my 1999 gsxr 750 srad edition no muffler and no cat just straight piped it didn't harm anything it just the bike overheated quickly though.
I ran a 99 600 like that for Summer Nationals when I did a few drag races and burnouts. The bike wasn't harmed at all.
 
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