quiet! exhaust

[teamKDRACING]

After deciding not to race this year to concentrate on work :-(

Have purchase a 4 stroke on/off road bike for summer fun - is pretty loud for road use :-(

If I split the out let pipe and fit two cans of a smaller bore, but equal to same 50mm straight through bore or slightly bigger i.e 2x 35mm - straight through- (perforated tube type) will it run quieter with same flow? it looks to have been done with big bore race super motos - I except the y piece will cause some upset in the exhaust gas but it's not a full on tuned race machine and quite basic.

Not enough room to fit a longer can of same bore - If I fit two of the same bore, I guess it may change tone but do little to DB volume @ 600cc

These larger piston single's seem to produce much more power through a gas flowed head and decent exhaust so last thing I want to do is strangle it..

too much noise not enough action

[RPD Motorsport]

For the application at hand - yes you can!

2 35mm pipes is in fact quite a lot more that your 50mm pipe, the CSA of 2 35mm is close to that of a 70mm pipe. Your right about the y-joint loosing some, and there are several other thing at work with harmonic waves in the flow of gas etc...

But its a pit bike! The differance would proberbly go un-noticed on a dyno let alone your bum! Just make it a bit easier on the ear, it wont do any damage or give a noticable change.

[phoenix]

Originally Posted by RPD Motorsport

For the application at hand - yes you can!

2 35mm pipes is in fact quite a lot more that your 50mm pipe, the CSA of 2 35mm is close to that of a 70mm pipe.

Not according to my calculator:

CSA 35mm dia = 962mm^2
CSA 35mm x 2 = 1924mm^2
CSA 50 mm dia = 1963mm^2
CSA 70mm dia = 3848mm^2

[teamKDRACING]

I'm not sure pit bike is an appropriate definition. - more like a 4 stroke motor cross bike with road wheels = road legal. i.e. super moto

Phoenix if I understand your calc correctly, 35mm x 2 = less flow than the single 50mm, oh bugger!
Was hoping for a tad more flow to compensate for any buffering at the junction etc.. be it low pressure / high flow.

The stainless pipe bore can actually increases at the y junction 1x 50mm in, by 2x 50mm exits, stepped down after.. so the restriction would only be in each end can at approximately 1ft long x 2.

Would simply feeding the same amount of gas flow through 2 separate cans @ 50mm same bore reduce the noise? i.e. same volume - or half the volume through each silencer, or in other words - same gas verse twice the surface area? no doubt not that simple? - I know the method would be make a longer silencer - any last advice? GIVE UP, you say!

I'm just embarrassed riding something that sounds like a Harley down our quiet street. It sounds justified when it being ridden hard (considered stupid) but sounds silly when puttering a long - like the exhaust has fallen off LOL.

I'm possibly 96 - 110db would like 55 - 75 db if possible

[phoenix]

Originally Posted by teamKDRACING

Phoenix if I understand your calc correctly, 35mm x 2 = less flow than the single 50mm, oh bugger!
Was hoping for a tad more flow to compensate for any buffering at the junction etc.. be it low pressure / high flow.

The difference isn't huge - less than 2% - and I doubt you would notice any performace drop. The excat size to match the 50mm would be 2 x 35.35mm, so you can see it's pretty trivial.

I would guess that half the sound energy would go down each of the two pipes - as would half the flow. So, in theory two cans with the same absorption capabilities of the one you have, fitted in parallel, should reduce the noise compared to one. But the best you can hope for is 10dB reduction (which is halving the sound pressure level) i.e. 100dB is half as loud as 110dB. Getting to 55dB will be a challenge!

[Tim Falce]

Originally Posted by phoenix

Getting to 55dB will be a challenge!

I would think it would be downright impossible, I thought 55db was just about the same as someone talking normally or normal ambient noise.

[teamKDRACING]

that maybe Tim - my bad

EN 352 Part 7 Level Dependent ear plugs. HSE CONTROL OF. NOISE AT WORK. REGULATIONS ... levels may be 85 decibels or more. Hearing protection must be made ...

I'm obviously expecting 85 DB to be loud enough, so was looking for a reduction to that.. I know I'm kicking out 96 DB+

I presumed 55DB was loud shouting level - obviously I'm wrong

I'm probably looking for 70-80 DB - if it's not going to drop below that - it's a waste of effort and additional weight.

thanks guys.

[phoenix]

Where are you measuring your 96dB and how?

85dB directly at your ear is going to be a lot louder than 85dB at 2 metres. That's why 1.8 watts of music into a pair of headphones is deafening when a 100 watt music system (8 times the volume) can be comfortable in a large room full of people at a party.

MSA Road Rally noise limits are 98dB at 0.5 metres from the exhaust exit measured at an angle of 45 degrees, or 86dB at 2 metres measured at the centre of the vehicle and 90 degrees to it - both at 3/4 of maximum engine rpm.

I assure you that such a level is about as quiet as most road cars straight out of the showroom - so not excessive by any means.

[teamKDRACING]

Track side readings indicate - 96 db? I'm no noise testing expert - that's running on the manufactures performance exhaust

- There is a one make that offers a bit better gas flow at the tail pipe exit + slightly bigger bore and has been reported at 100 DB..

- I'm not using mine at the track but they are turning them away now - it's a sound note that really travels, hence why they are perhaps starting to run two exhausts silencers?

It is obviously more quiet at certain rpms not constant, but thumps under power - even gentle throttle is attention seeking - it sounds louder at points in the rpm range which may be frequency - somewhere in the mid range when it's revving a bit to lean the throttle - it actually sounds less of a thumper.

Other than drag racing cars - it's sounds loud when considering the low frequency - it's a bit silly for road use - I do not recall hearing anything this loud on car race testing days - maybe historic open pipe stuff?

It has two pipes exiting the head at approximately 30/35mm o.d. each going into one pipe at 45/50mm o.d. - The baffled can is reported to make them asthmatic and robs power and will run hot a throw away item.

I'm gonna try repacking it - before I get the grinder out.

Thanks for the replys guys