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Discussion Starter #1
I am on my third zx10r, due to two of them being stolen. Anyways my 05 had a fully muzzy titainium (loved it). Then the 07 was stock and now I have anouther 07 stock. I played around with my 05 and took the can off and drove it with just the headers and pipe to the can. Lost tons of low end torque. I guess my real question would it be possible to keep torque if removed the catalitic converter and cans and used the some of the portion of the pipe that connected to the cans as an exhaust. I see all these moto gp styling systems and wonder how they make low end torque?
 

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the key to a good exhaust is back pressure. If there's good flow, then that allows for more suction in the cylinder head for fresh air + fuel. If there's positive pressure, then you get less fresh air and fuel, and maybe even some used smoky air that hangs around or is pushed back in the engine. That's why you see the 4-2-1 arrangement, not 4-1 for exhausts.

Also, those gp mufflers WERE designed, not just chopped (but close to it, it seems!). Remember, high-end power is desirable on the track, low end torque for street, smooth power band for all. So, all those "hp gains" from exhausts may be just in the upper end, which is why it's always nice to see dyno charts on the manufacturer's website - does it give you top end or more midrange, both, or not much of anything? For example, the Akrapovic full for gen 3 gives generous midrange improvements, as well as some top end. Worth checking out.

Probably not an absolute / 1000% complete answer, but it gets you thinking in the right direction anyways...
 

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The issue isn't really "back pressure"; the issue is actually timing the pressure waves and pulses that move through the exhaust system because the flow is highly unsteady. If the exhaust system is designed to send a negative pressure wave to the cylinder just before the end of the exhaust stroke, during the time that the intake and exhaust valves are both open, the negative pressure wave goes right through the cylinder and starts pulling air through the intake tract before the piston even starts moving down. But, a consequence of an exhaust system designed for maximizing this pulse tuning, is that it will have back pressure. The back pressure *itself* is not desirable (this is why a plain ordinary restriction in the exhaust system will do nothing but kill power), but it is a necessary side effect of an exhaust system designed for best scavenging.

So what happened when you took that muffler off ... It had the effect of making the total length of the exhaust system shorter, which means a shorter time between the positive pressure wave being sent out from any given cylinder and the reflection of that wave as a negative pressure wave. Effectively it re-tuned the exhaust system to operate at a higher RPM, beyond the effective range that the engine can use.

Keep in mind that the MotoGP engines are making peak power near 16,000 rpm or thereabouts, so they need a shorter exhaust system. What works in their 16,000 rpm application might not work in your lower-revving application. A lot of the recent under-the-bike exhaust systems have some interesting arrangements inside those containers in order to make their effective length longer.
 

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True true. If you wanna get technical, then obviously you are right. I just wanted to shine a little light for speedzx10r, and if he really wanted to, he could learn more about it. Thanks for the more accurate version though. I'll never be sad to see good info posted up for all to see!
 

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Discussion Starter #6
Hey thanks for the input... Good info, I am just trying to be cheep to get a moto gp exhaust. Looks like I will have to fork over the money.
 

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The issue isn't really "back pressure"; the issue is actually timing the pressure waves and pulses that move through the exhaust system because the flow is highly unsteady. If the exhaust system is designed to send a negative pressure wave to the cylinder just before the end of the exhaust stroke, during the time that the intake and exhaust valves are both open, the negative pressure wave goes right through the cylinder and starts pulling air through the intake tract before the piston even starts moving down. But, a consequence of an exhaust system designed for maximizing this pulse tuning, is that it will have back pressure. The back pressure *itself* is not desirable (this is why a plain ordinary restriction in the exhaust system will do nothing but kill power), but it is a necessary side effect of an exhaust system designed for best scavenging.

So what happened when you took that muffler off ... It had the effect of making the total length of the exhaust system shorter, which means a shorter time between the positive pressure wave being sent out from any given cylinder and the reflection of that wave as a negative pressure wave. Effectively it re-tuned the exhaust system to operate at a higher RPM, beyond the effective range that the engine can use.

Keep in mind that the MotoGP engines are making peak power near 16,000 rpm or thereabouts, so they need a shorter exhaust system. What works in their 16,000 rpm application might not work in your lower-revving application. A lot of the recent under-the-bike exhaust systems have some interesting arrangements inside those containers in order to make their effective length longer.
GREAT post, collector arrangment plays a role here as well, this is why I chose Arrow over the others.
 

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2 words my friend; RACEFIT GROWLER!
ESPECIALLY for the 2ng gen! :drool:
:+1:

Damn straight, wish those guys would make headers/collectors!!! I would definately be in line if they ever offered.
 

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The issue isn't really "back pressure"; the issue is actually timing the pressure waves and pulses that move through the exhaust system because the flow is highly unsteady. If the exhaust system is designed to send a negative pressure wave to the cylinder just before the end of the exhaust stroke, during the time that the intake and exhaust valves are both open, the negative pressure wave goes right through the cylinder and starts pulling air through the intake tract before the piston even starts moving down. But, a consequence of an exhaust system designed for maximizing this pulse tuning, is that it will have back pressure. The back pressure *itself* is not desirable (this is why a plain ordinary restriction in the exhaust system will do nothing but kill power), but it is a necessary side effect of an exhaust system designed for best scavenging.

So what happened when you took that muffler off ... It had the effect of making the total length of the exhaust system shorter, which means a shorter time between the positive pressure wave being sent out from any given cylinder and the reflection of that wave as a negative pressure wave. Effectively it re-tuned the exhaust system to operate at a higher RPM, beyond the effective range that the engine can use.
What the packpressure does is increase the density of the exhaust gasses, which in turn makes those waves stronger, but only to a point of diminishing returns. These 'waves' effectively collapse at the end of the header pipe though, or where there is a 'y' in the pipe so aren't so relevant in the tailpipe. Gas velocity is though, and the kinetic energy from the column of gas moving through the pipe prevents backflow up the headers following that negative pressure wave and effectively enhances the vacuum at the end of the header when the wave collapses. Too much backpressure prevents the negative pulses from forming properly though.
 

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What the packpressure does is increase the density of the exhaust gasses, which in turn makes those waves stronger, but only to a point of diminishing returns. These 'waves' effectively collapse at the end of the header pipe though, or where there is a 'y' in the pipe so aren't so relevant in the tailpipe. Gas velocity is though, and the kinetic energy from the column of gas moving through the pipe prevents backflow up the headers following that negative pressure wave and effectively enhances the vacuum at the end of the header when the wave collapses. Too much backpressure prevents the negative pulses from forming properly though.
Was thinking the same thing along with the pairing of cylinders from an exhaust perspective. :wink:
 

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Forget the growler..go get a beet full system..
 

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Have a look at any dyno result using a growler and see if you can find the midrange............
 

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Have a look at any dyno result using a growler and see if you can find the midrange............
Serious? It may not be saying much but at Fenders where I had it tuned, the only bike that made more torque was an 05 Gsxr that was turboed. I could take a picture with my cell phone of one of my graphs as well...:rolleyes:
 

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Very serious - a lot of dyno operators won't run them as they either cause problems or show zero/negative gains.
And they are also stupily noisy.
Think about how much time Akra, Arrow, etc put into the design/testing of theirs and then how much was out into the growler - 10mins with a pencil and paper and a pic of Rossi's bike.
Nothing else.
 

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Discussion Starter #17
Well I just put on a Speedohealer. Was a good install... And back wishing for more power from a stock exhaust. I have to get rid of my cat...
 

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Backpressure will richen the mixture due to an increase in unburnt gasses, but won't help hp or torque.....overall. It just so happens that smaller pipe constrictions that help low RPM hp and torque will be too "tight" for high rpm.

The problem with exhaust is that it does get tuned to a particular rpm and flow. You can't always have your cake and eat it too at ALL rpm's.

First understand Bernoulli's principle. It's exactly why carb venturis work to atomize fuel.

http://en.wikipedia.org/wiki/Bernoulli's_principle

Basically, the right constriction can create a low pressure area and actually create some suction to help remove unburnt exhaust gasses. A smaller diameter header will draw well at low rpms and then not flow fast enough at high rpms. Smaller and often longer header diameters will increase torque and HP at low rpm while shorter and larger diameters will increase hp and torque at high rpms. Header collectors and crossover pipes can tune the pulses between cylinders to the pulses from other cylinders to help draw exhaust flow out of the chamber.

To a lesser extent this also applies to mufflers.....length, air friction and constriction will matter.

In most cases "backpressure" will richen the mixture (by replacing fuel with contaminants) and will reduce horsepower, but in extreme cases where the exhaust hole is so large, you will lose the venturi effect where there is a suction drawing the burnt gasses out and the fresh mixture in......kind of a supercharging effect (but not really since it's just air pressure).

Depending on the cam overlap (the time when both intake and exhaust valves are open) there can be enough flow that fuel and intake gasses can actually be pulled into the exhaust.

Bikes operate a LARGE variance in rpms.....more so than american cars that we are often used to. You can tune the engine to gain hp in either the lower or upper rpm range, but it's harder to make gains across the rpm range.....when you do it can often be at the expense of fuel efficiency (as if we care).

I'm an old car racer so I just tried to make the process easily understandable.
 

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To add to the previous info, many principles come into play with exhaust design,( Bernoulli's being one of the many). An easy way to think of the 4-2-1, vs 4-1, vs 1x4, is to think of an old pipe organ. Each pipe has a frequency that the volume of gas in it wants to vibrate at, (resonance). A single pipe of a given diameter and length will have a certain frequency, (rpm) it particularly likes. So simply put, single tube exhausts will work best in a narrow, focused rpm range, (i.e., zoomies on NHRA Top Fuel and Funny Car), 4-1's broaden that range by adding a collector, 4-2-1's attempt to widen the usable range further.
An engine is nothing more than a heat powered air pump. But less than 35% of the heat it generates propels you forward, the remaining energy does nothing but get dissapated into the air. A tuned exhaust tries to use some of that heat,(expanding exhaust gasses, resultant pressure waves, etc.), to initiate the next intake cycle, (during valve overlap). The more air you can pull into engine, the more fuel you can add to the party. The greater the restriction, (back pressure), the more heated and contaminated,(by exhaust gasses), the intake charge will be. Bore, stroke, valve sizes, intake length, etc., etc., add to the complexity of the exhaust diameter, length, taper puzzle. This usually creates a compromise, in a less sharpened peak efficiency for wider range. Get it all right though, and you can achieve "supercharging". Defined by better than 100% volumetric efficiency, or, higher than atmospheric pressure in the cylinder when the intake valve closes. But it will generally occur over a relatively narrow RPM range.
 
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