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is lurking in the shadows
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3,859 Posts
Discussion Starter · #1 ·
I've got a 02 F4i and I've been wanting to ditch the stock exhaust because it's just plain huge. Instead of making a shortie out of it, I want it to stop right after the headers, but I dont want to do anything to lose backpressure and hurt performance. Is there anything I could do?
 

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Function IS Form
19 Z900, 88 Kat11
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17,433 Posts
Exhaust gas dynamics would dictate you gain power at the high end and lose it on the low end with a shorter exhaust. The only thing keeping your bike from running right would be an ECU that's not compensating for the additional airflow and scavenging... The solution being a Power Commander III...

If you want to make an exhaust that comes right off the headers, you can:

Weld a tip to the header, and weld a baffle inside of it if you want (this will reduce airflow and reduce your need for a Power Commander)
You can also weld or adapt a muffler to the end of the header (probably will require a length of pipe to change the angle), a muffler shortened to 4-5 inches looks and sounds pretty tight like that.
 

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is lurking in the shadows
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3,859 Posts
Discussion Starter · #4 ·
I chopped the exhaust on my R1 like this. Stuffed it with packing and a Samson baffle and it runs like raped ape. Powdercoated a automotive muffler tip to top if off.
Lol it was your R1 that made me want to do this. It's currently the background on my laptop. If you could PM me with slightly more detailed directions on what you did that would be FN great.
 

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A New Breed
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763 Posts
I used a Samson Shortie Baffle and 4-stroke fiberglass packing. Both easily found online. Probably around $35-$40 for both. Then found a chromed automotive tip at a local parts store and had it powdercoated. Wrap the baffle with the packing and then stuff it into the end of the header. Secure it with the set screw and you're ready to go. Just chop the pipe with a sawzaw or hacksaw.
 

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Function IS Form
19 Z900, 88 Kat11
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17,433 Posts
Careful with the fiberglass, it's nasty stuff
I wear gloves and goggles when I handle fiberglass
 

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Member
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98 Posts
I used car-craft baffles in mine from summit racing (sorry lazy with the linkage, you can search summitracing.com) they are meant for open header drag cars - surprisingly dont quiet as much as i thought... I also added extra packing, can get it from any motorcycle store, i used motorcycle superstore or something, i dont remember.

Jesse Rooke uses FMF power bombs on some of his bikes too, they seem pretty sweet, and super unobtrusive, but i dont know how loud or quiet they are.
 

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Function IS Form
19 Z900, 88 Kat11
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17,433 Posts
Would would this do to my exhaust pulse scavenging and gas velocity, you mean. Backpressure doesn't make torque!

And it will degrade it very much.
 

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British Bloke in Canada
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2,146 Posts
I used a VW beatle baffle in my cut down yoshi, worked out great!!
dont feck with the headers, you can play with the can lenth without too much problems, when I first shortend my can it seemed to make the bike run leaner, so I had my bike adjusted with the yosh box,
 

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Function IS Form
19 Z900, 88 Kat11
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17,433 Posts
Leave your exhaust the same length, and use a Power Commander to retune it when you modify it.

The length of your exhaust and the diameter of the pipe determine your powerband. The resistance to the gasses moving (baffles, packing) only reduces power at all points.
 

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the mad doctor
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3,399 Posts
Leave your exhaust the same length, and use a Power Commander to retune it when you modify it.

The length of your exhaust and the diameter of the pipe determine your powerband. The resistance to the gasses moving (baffles, packing) only reduces power at all points.

not 100% true, b/c the length of the pipes, and the diameter, change the resistance of the exhaust flow, just in a different way. it tends to be a smoother transition than the abruptness of a baffle or muffler, etc.
 

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Function IS Form
19 Z900, 88 Kat11
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17,433 Posts
The length of the pipes determine the frequence of the scavenging pulses (thereby which rpms they have an effect), and the diameter determines the velocity of the gasses (venturi effect)
 

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the mad doctor
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3,399 Posts
The length of the pipes determine the frequence of the scavenging pulses (thereby which rpms they have an effect), and the diameter determines the velocity of the gasses (venturi effect)

both of which determine overall resistance of the exhaust flow.

there's soooo much to it, but unless you study it, alot of it doesn't make sense, just trying to keep it relatively simple for those that haven't. but yeah, haelo, you are correct.
 

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Function IS Form
19 Z900, 88 Kat11
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17,433 Posts
I was talking more along the lines of backpressure, which people seem to think makes torque for some reason... ???
 
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