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Inside the cans, you have your perforated metal that is wrapped in packing. Why perforated metal? Don't you want your exhaust going straight out the back of the muffler? Wouldn't a solid piece work better?

2nd Question:
How does the size of the holes in the perf. metal play a role? What would larger holes do?

Thanks guys!!
 

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with a straight through tube u will loose torque, but gain a tiny bit on the top end. u need a certain amount of backpressure to run right. the larger holes i cant be sure how it would effect performance, but i think it would make it quieter by allowing more exhaust flow through the packing.
 

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exhausts need to juggle the bike's emissions, noise, torque and horsepower. A Graham Bell has written extensively on the effect of exhaust tuning on performance for two and four stroke engines. For a quick read try searching the internet for "Helmholtz resonance."

The perforated metal allows sound to be partially absorbed by the exhaust packing while the hot gasses continue out the end of the exhaust pipe. Think about tuning as a means to achieve a goal (high horsepower, high torque, wide powerband, best fuel economy) and not better or worse. A solid exhaust is going to have different performance characteristics then an exhaust with packing. If it's better or worse is up to you. The size of the holes in an exhaust has to so with Helmholtz resonance. Helmholtz figured out that having holes will do a lot to dampen out the sound of the exhaust while still allowing the engine to exhale.

As for the size of the holes, remember velocity increases when pipes are increased. for example if you had 10 psi coming out of a garden hose that would be a lot of pressure but if you had 10 psi coming out of a fire hose it would be only a trickle. the garden hose will have higher pressure but will eventually be too restrictive to flow a lot of water. this is why long, skinny exhausts give you low and mid-range performance at the expense of top end speed. the same is true of short, fat exhausts only in reverse.
 

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exhausts need to juggle the bike's emissions, noise, torque and horsepower. A Graham Bell has written extensively on the effect of exhaust tuning on performance for two and four stroke engines. For a quick read try searching the internet for "Helmholtz resonance."

The perforated metal allows sound to be partially absorbed by the exhaust packing while the hot gasses continue out the end of the exhaust pipe. Think about tuning as a means to achieve a goal (high horsepower, high torque, wide powerband, best fuel economy) and not better or worse. A solid exhaust is going to have different performance characteristics then an exhaust with packing. If it's better or worse is up to you. The size of the holes in an exhaust has to so with Helmholtz resonance. Helmholtz figured out that having holes will do a lot to dampen out the sound of the exhaust while still allowing the engine to exhale.

As for the size of the holes, remember velocity increases when pipes are increased. for example if you had 10 psi coming out of a garden hose that would be a lot of pressure but if you had 10 psi coming out of a fire hose it would be only a trickle. the garden hose will have higher pressure but will eventually be too restrictive to flow a lot of water. this is why long, skinny exhausts give you low and mid-range performance at the expense of top end speed. the same is true of short, fat exhausts only in reverse.
Well done! Looks like my response isn't needed, wasn't going to be nearly as good.
 

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exhausts need to juggle the bike's emissions, noise, torque and horsepower. A Graham Bell has written extensively on the effect of exhaust tuning on performance for two and four stroke engines. For a quick read try searching the internet for "Helmholtz resonance."

The perforated metal allows sound to be partially absorbed by the exhaust packing while the hot gasses continue out the end of the exhaust pipe. Think about tuning as a means to achieve a goal (high horsepower, high torque, wide powerband, best fuel economy) and not better or worse. A solid exhaust is going to have different performance characteristics then an exhaust with packing. If it's better or worse is up to you. The size of the holes in an exhaust has to so with Helmholtz resonance. Helmholtz figured out that having holes will do a lot to dampen out the sound of the exhaust while still allowing the engine to exhale.

As for the size of the holes, remember velocity increases when pipes are increased. for example if you had 10 psi coming out of a garden hose that would be a lot of pressure but if you had 10 psi coming out of a fire hose it would be only a trickle. the garden hose will have higher pressure but will eventually be too restrictive to flow a lot of water. this is why long, skinny exhausts give you low and mid-range performance at the expense of top end speed. the same is true of short, fat exhausts only in reverse.
Yep, like that. Similar effects with hydraulics. Look at the loads they can push with relatively limited pressure.
 

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While we're on the subject, just picked up a smokin' deal on a brand new full Fast by Ferracci system. The header pipe is a larger O.D. than my stocker, so will my main jet need bumped up? The silencer looks about the same, just made out of Ti.
 

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oldskool, OD is less important then ID, which will determine the velocity of gasses exiting the head. If we assume the ID is equally larger I don't know if/how much you will have to change your jetting but this will no doubt rob you of low/mid range power (larger pipe means less pressure and slower gas velocity) but boast your high range power (the larger pipe is less restrictive and will flow a greater volume of gas). I'd do some test runs and see if the bike is popping on deceleration (a sign that the jetting is too lean) or if the bike is running sluggish and asthmatic (a sign that the jetting is too rich). It's also good to note if the bike starts easier/harder when the bike is cold/hot. Rich bikes tend to start easy when they are cold but have trouble starting when they are warm and vice versa.
 

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exhausts need to juggle the bike's emissions, noise, torque and horsepower. A Graham Bell has written extensively on the effect of exhaust tuning on performance for two and four stroke engines. For a quick read try searching the internet for "Helmholtz resonance."

The perforated metal allows sound to be partially absorbed by the exhaust packing while the hot gasses continue out the end of the exhaust pipe. Think about tuning as a means to achieve a goal (high horsepower, high torque, wide powerband, best fuel economy) and not better or worse. A solid exhaust is going to have different performance characteristics then an exhaust with packing. If it's better or worse is up to you. The size of the holes in an exhaust has to so with Helmholtz resonance. Helmholtz figured out that having holes will do a lot to dampen out the sound of the exhaust while still allowing the engine to exhale.

As for the size of the holes, remember velocity increases when pipes are increased. for example if you had 10 psi coming out of a garden hose that would be a lot of pressure but if you had 10 psi coming out of a fire hose it would be only a trickle. the garden hose will have higher pressure but will eventually be too restrictive to flow a lot of water. this is why long, skinny exhausts give you low and mid-range performance at the expense of top end speed. the same is true of short, fat exhausts only in reverse.

10psi through a garden hose is the same as 10psi through a fire hose,the pressure is the same,it's the flow that is different,10psi can't be higher than 10psi :headscrat
 

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correct, 10 psi is the same no matter when is coming from. i mistyped pressure when I meant volume. so 10 gallons per minute out of a garden hose versus 10 gallons per minute out of a garden hose.
 

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correct, 10 psi is the same no matter when is coming from. i mistyped pressure when I meant volume. so 10 gallons per minute out of a garden hose versus 10 gallons per minute out of a garden hose.
yeah cool,kind of guessed it was a typo,pretty sure you knew the score,people always get pressure and flow mixed up so was just making an observation,cheers kev
 

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oldskool, OD is less important then ID, which will determine the velocity of gasses exiting the head. If we assume the ID is equally larger I don't know if/how much you will have to change your jetting but this will no doubt rob you of low/mid range power (larger pipe means less pressure and slower gas velocity) but boast your high range power (the larger pipe is less restrictive and will flow a greater volume of gas). I'd do some test runs and see if the bike is popping on deceleration (a sign that the jetting is too lean) or if the bike is running sluggish and asthmatic (a sign that the jetting is too rich). It's also good to note if the bike starts easier/harder when the bike is cold/hot. Rich bikes tend to start easy when they are cold but have trouble starting when they are warm and vice versa.
True, the ID and OD will be bigger. The way the theory works, I was wondering about losing some on the low end. I guess there is a tradeoff with everything. Currently I have gobs of power down low and mid. I'm not after top speed per say, just like to have some more ponies coming out of sweepers. Liter bikes can spoil you:lol: This pipe should be here next week, hope it wakes the top up without robbing too much down low.

Thanks for your input too:thumbup:
 
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