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Discussion Starter #1
Hello!

I've finally taken the plunge and decided to de-clutter my little CBR400RR. I removing the shitty DIY SS free-flow exhaust and planning to fit an under-body shorty in it's place.

Currently the bike has a 4:2:1. The 4:2 section is great, the 2:1 is seriously fucked up with rust. It's so bad that I'm going to censor it in the pictures.

Anyway, there is the before pic:



Here is a crappy paint design I'm thinking of using (not to scale):



My question is should I link the two pairs together to balance them? One side will be shorter if I use this design. Maybe I should Rebulid the 2:1 section in the muffler and split again for the twin hole design.

I've got a nice little DC inverter MMAW setup. I'm planing on using mild steel; I don't care if it rusts away after 2/3 years; I'll replace it before then.

Any suggestions or criticisms are welcome.

Cheers,

Chris
 

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Commander Cool
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ok. for starters, the valves in these engines are TINY. losing backpressure could result in them burning out very rapidly. secondly, without baffling this will be very loud and more than likely shoot flames all over your foot.

you'll need to keep the pipes the same length, otherwise one end will scavenge faster than the other and result in misfires.

otherwise, this is pretty cool; I used to have the 250rr and loved the way they sounded.
 

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Discussion Starter #3
ok. for starters, the valves in these engines are TINY. losing backpressure could result in them burning out very rapidly. secondly, without baffling this will be very loud and more than likely shoot flames all over your foot.

you'll need to keep the pipes the same length, otherwise one end will scavenge faster than the other and result in misfires.

otherwise, this is pretty cool; I used to have the 250rr and loved the way they sounded.
Good points. In that case I'll go with something like this:



The blue stuff is a probably going to be SS wool. The orange thing is a baffle. I use half moon slits. I'm guessing that I should try to keep the flow rate of the muffler chamber similar to the headers to stop the exhaust gas from slowing down.
 

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I'd still wanna run it with two outlets after the baffle....

:D
 

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When I was trying to decide on mine I was looking at various options...

One was very similar to that. except, I was Gunna do the baffled section like a shortened sidepipe .. with the perforated outer sleeve (err...sorta,like an AC cobra but with dual tips)


SAD, I know... But I liked it
 

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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.
 

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clean fight
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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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Discussion Starter #12
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.

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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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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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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V four honda whore
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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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The friendly Ghost.
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