An article about back pressure !!!

[fortress]

If i understand well, too much back pressure is not good, and less, is good!! like aftermarket company tell to us!! I know, alot of people tell that is not true but.. this article tell something else!!

FLOW SYSTEM tuned-pipe, expansion chamber exhaust systems are Helmholtz resonators. This is a fancy term for a big long tube that works like an organ pipe. Above a certain rpm, the engine exhaust pressure pulses (coming out of the cylinder head and going into the pipe) create a standing acoustic (sound) wave inside the pipe. Here's an analogy... When you sing in the shower, the sound will suddenly seem louder at certain notes. That is because the size of the shower is "tuned" to the particular note your are singing and begins to resonate (get louder). In the FLOW SYSTEM pipe, the sound wave bounces back and forth inside the big chrome section and creates a lower pressure region right where it is bolted to the cylinder head. This lower pressure actually sucks the exhaust gas out of the cylinder thereby making more room for fresh charge of fuel and air. More fuel in the cylinder means: 1. more energy to drive the piston down, and 2. more power for your 'Ped. Tuned pipes are by their very principle of operation more efficient than other, less-expensive aftermarket mufflers that simply reduce back pressure (the ones that are about the same size as the stock muffler but have twin exhaust tubes). Simple, low-restriction mufflers don't create low pressure at the exhaust port of the cylinder head like tuned pipes do. They just slightly reduce back pressure. Back pressure is the pressure that builds up at the exhaust port of the cylinder head when the engine is in operation. The exhaust wants to flow out of the exhaust port but the limited flow area in the muffler prevents it from flowing freely. For instance, when you try to blow through a drinking straw, you build up "back pressure" in your cheeks. Too much back pressure will keep a full, fresh charge of fuel/air mixture from entering the cylinder on the intake stroke. If a full charge of fuel/air mixture can't enter the cylinder then you will lose power. That's why excessive back pressure is a bad thing.

 

[MrSled]

that really great info

 

[Ding]

Good overview of back pressure.

One thing to note is that the size, volume, and shape of the tuned pipe, along with the size and placement of the exit have a direct effect on the resonance, and pulsing of the air flow through the pipe. What pipe builders attempt to do is cause the pulse of air that bounces back toward the cylinder to be timed just right that at a certain temperature and rpm the optimum amount of fresh fuel charge that has come through the cylinder and out the exhaust port gets forced back into the cylinder just before the port is closed. Change any of the contributing factors, and performance suffers. This is why pipes make best the HP at a usually small rpm range. It is also why jetting is so critical with aftermarket pipes. If you fall off the optimum range for any reason, the volume, and ratio of the air/fuel mixture in the combustion chamber is changed. There is another story to tell on that topic as well as the CDI interaction, but I'll leave those for someone else.

 

[fortress]

Good overview of back pressure.

One thing to note is that the size, volume, and shape of the tuned pipe, along with the size and placement of the exit have a direct effect on the resonance, and pulsing of the air flow through the pipe. What pipe builders attempt to do is cause the pulse of air that bounces back toward the cylinder to be timed just right that at a certain temperature and rpm the optimum amount of fresh fuel charge that has come through the cylinder and out the exhaust port gets forced back into the cylinder just before the port is closed. Change any of the contributing factors, and performance suffers. This is why pipes make best the HP at a usually small rpm range. It is also why jetting is so critical with aftermarket pipes. If you fall off the optimum range for any reason, the volume, and ratio of the air/fuel mixture in the combustion chamber is changed. There is another story to tell on that topic as well as the CDI interaction, but I'll leave those for someone else.

Well, so, installing an aftermarket silencer that are designated specially for a type sled, is not a bad thing like people are saying according to this article, cuz it reduce the back pressure a little at the exhaust port!!

 

[Ding]

Just the sliencer alone won't do much, unless the restriction in the silencer is significant enough to affect the pipe. This is the case with many stock setups, especially on models from a few years ago. Now if you are referring to the whole pipe, then yes you may get a more HP at a certain rpm, but you usually lose HP at other rpms. If you are able to jet (full circuit) to get the most power, clutch to get to the optimum rpm and stay there, get the power to the ground without spinning, and the type of riding or racing you do fits this profile, then aftermarket pipes can give you significant gains.

Manufacturers design the stock pipes with performance as well as several other factors in mind including driveability, reliability, varying conditions, varying riding types and styles, fuel economy, noise, production costs, etc.

 

[fortress]

Just the sliencer alone won't do much, unless the restriction in the silencer is significant enough to affect the pipe. This is the case with many stock setups, especially on models from a few years ago. Now if you are referring to the whole pipe, then yes you may get a more HP at a certain rpm, but you usually lose HP at other rpms. If you are able to jet (full circuit) to get the most power, clutch to get to the optimum rpm and stay there, get the power to the ground without spinning, and the type of riding or racing you do fits this profile, then aftermarket pipes can give you significant gains.

Manufacturers design the stock pipes with performance as well as several other factors in mind including driveability, reliability, varying conditions, varying riding types and styles, fuel economy, noise, production costs, etc.

i'm just talking about aftermarket silencer.. So, it won'T be has bad as people are talking!! I have an mbrp can and my rpm now reach 8800 8900 instaed of 8500 with my stock silencer!! I need to add weight to bring down the RPM.. Turk tell me its not necessary due to a power increase... Well, what's i understand here, is if i need to add more weigth to my cltuch, its cuz the engine pull harder!! no?!?

 

[Ding]

I would guess that the efficiency of the clutches has somehow changed. Springs weaken, parts bind, belts wear or are different widths, etc.

I have never heard of an aftermarket silencer that made that much difference.

If you still have your stock exhaust silencer, throw it back on and check rpm. That is the only way to be sure that the silencer alone made the difference.

 

[fortress]

I would guess that the efficiency of the clutches has somehow changed. Springs weaken, parts bind, belts wear or are different widths, etc.

I have never heard of an aftermarket silencer that made that much difference.

If you still have your stock exhaust silencer, throw it back on and check rpm. That is the only way to be sure that the silencer alone made the difference.

YOur probably right, but me i have heard different story.. My last ride last year, my rpm was normal!! Well, i have an appointment to my yammy dealer tonight, to check my clutch alignement, worn part etc etc. I will make another test ride after.. Maybe, like you said, its just worn part...!!

but at the end, it cannot be as bad has people are sayuing