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Old Streetfighter Motorcycle Forum Post 02-05-2012, 12:42 PM   #11
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Default Re: DIY under-body exhaust - CBR400RR

and then there are guys on here who run a slash-cut midpipe and thats it. so do what ya want and be prepared to not like it and change it if it isnt good. youve got very little to loose if you are testing it out using cheap materials that you already have.
exept if you burn up valves. which i dont know anything about.
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Old Streetfighter Motorcycle Forum Post 02-06-2012, 03:56 AM   #12
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Default Re: DIY under-body exhaust - CBR400RR

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Originally Posted by Mustapha dump View Post
Just get you system repaired, fitting an under engine silencer like that will not make the bike run better. You'll lose midrange. Exhaust systems are the length and design they are for a very good reason. Cutting out 18 inches or so of the midpipe will screw up the resonance needed for the scavenging pulses. A short open pipe is fine if you are on the strip and just going flat out wide open throttle all the time, and you just need the spent gases out as fast as possible, but in the real world on a roadbike, you want to retain the low and midrange performance. The little 400cc bikes lack torque to start with, and with what you're intending you'll lose the little available torque you have.
I've seen all manner of exhaust systems fitted to the bikes that I've had in for setting up on my dyno, and the best performance is from a stockish style of pipe, underseat systems mess up the midrange just as the under motor systems do, same thing, by adding another 18 inches or so into the exhuast system again plys havoc with the resonance and timing of the scavengine pulses, bikes that have underseat systems or under engine systems as stock are designed from the outset to run with them, and will have different cam timing, ignition, etc to take use the increase or decrease in pipe length.
Look at the various aftermarket exhaust systems available for your particular model, they all look pretty similar in construction and design, that isn't a coincidence, it is because the design layout works best through the entire rev range.
Just the information I am looking for. Now I know what to expect. I'm going to give it a go anyway as a little experiment and to quell my curiosity. I will probably in the end, do as you suggest. The bike was running a stupid open SS 2'' can. It was loud as fuck. I ended up make a small reflective baffle the reduced the noise and improved the low and mid-range torque. The high end suffered a bit, but then again I don't need to travel around at 190kph in town.

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Originally Posted by leo_black_label View Post
and then there are guys on here who run a slash-cut midpipe and thats it. so do what ya want and be prepared to not like it and change it if it isnt good. youve got very little to loose if you are testing it out using cheap materials that you already have.
exept if you burn up valves. which i dont know anything about.
Yep, I'm going to experiment. The old setup was very free flowing, I baffled it a bit for back pressure and to protect the valves. My design above uses a reflective (restrictive?) and absorption baffle. This should increase back pressure and protect the valves.


This bike is a project bike; I don't use it to commute. So if I mess up it is not the end of the world. I an however planning to use it for my EE B-Tech project.

Thanks again for the advise guys!
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Old Streetfighter Motorcycle Forum Post 02-06-2012, 02:48 PM   #13
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Default Re: DIY under-body exhaust - CBR400RR

hey mustapha,

what about increasing the mid pipe length? will that affect anything negatively?

my plan with an underbody involves a few bends, and I believe, an overall incease in length of the system. (maybe, it still may not fit)
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Old Streetfighter Motorcycle Forum Post 02-06-2012, 03:41 PM   #14
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Default Re: DIY under-body exhaust - CBR400RR

If your very clever with a bender / welding set you could loose the intermediate pipe length under the bike by curling it back round !

e.g


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Old Streetfighter Motorcycle Forum Post 07-07-2020, 01:00 PM   #15
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Default Re: DIY under-body exhaust - CBR400RR

ARISE THREAD!!! LIVE AGAIN!!!

I would like to do something similar with a F800r. How did this end up?

Thank you for all your content!
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Old Streetfighter Motorcycle Forum Post 07-07-2020, 01:37 PM   #16
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Default Re: DIY under-body exhaust - CBR400RR

OP has not been back since 2012. You can try to PM him and hope he has notifications enabled and still has the same email address.

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yell, "Built not bought mother fucker!" in there face and then spit on their bike and walk off.
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Old Streetfighter Motorcycle Forum Post 09-28-2020, 05:13 AM   #17
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Default Re: DIY under-body exhaust - CBR400RR

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OP has not been back since 2012. You can try to PM him and hope he has notifications enabled and still has the same email address.
do you still have the same email from 2012?

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Old Streetfighter Motorcycle Forum Post 09-28-2020, 08:06 AM   #18
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Default Re: DIY under-body exhaust - CBR400RR

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do you still have the same email from 2012?

yeah, i have the same one from 2002 at least
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Old Streetfighter Motorcycle Forum Post Yesterday, 12:04 AM   #19
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Default Re: DIY under-body exhaust - CBR400RR

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do you still have the same email from 2012?
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yeah, i have the same one from 2002 at least
I have my first two personal emails and regularly use both, only ones I have lost are different schools and different work places.




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