R1000 Posted June 7, 2008 Share Posted June 7, 2008 A short time ago I tested to use a dB-killer on the Bird. The reason was to be prepared for MOT. My Bird has an Akrapovic 4-2-1 system. The result was that the dB-killer almost killed the engine. No power above 8 k or so. I then modified the dB-killer so the only remaining part of it was a restriction of 5 mm at the end of the muffler. Same result, the power level was much lower than without the dB-killer. It seems that my bike with ported head and other camshafts is very sensitive to any restriction in the muffler. This guided me to now test a less restrictive muffler. I had a race-baffled Yoshi TRS muffler in the garage and just installed it after the Akra midpipe. The Yoshi muffler ID is 57 mm vs. 52 mm on the Akrapovic. The difference in area is 20 % The 5 mm gap between the mid pipe and the muffler was sealed with a number of 0.5 mm Teflon sheet layers, until it was suck-tight. Result, the engine definitely feels stronger, it gave 153 rwhp before and it must be a bit above 155 rwhp now since I can feel the difference to the better so easy. The sound is also more Jet-like, without being annoying sharp. Low rpm performance has not been affected at all, at least not to the negative side. The TRS muffler is about 10 cm shorter than the Akra muffler so it looks a bit more slim on the bike. As it feels right now, the Akra muffler will stay on the Bird, which is a bit stronger than before . The sound level is a bit high after all... http://www.youtube.com/watch?v=pSbc24KO9oI Quote Link to comment Share on other sites More sharing options...
R1000 Posted June 14, 2008 Author Share Posted June 14, 2008 The first measurement was incorrect, the meter was to near the pipe and the rpm was to high. On this video the values are correct, the meter have also been checked to read only 0.1 dB wrong in a certified test lab. http://www.youtube.com/watch?v=OGYs0oQIsuE Quote Link to comment Share on other sites More sharing options...
CxBXR Posted June 14, 2008 Share Posted June 14, 2008 Only a ~2 db difference, is it worth the HP loss ? Will it pass for MOT or is more reduction needed ? Quote Link to comment Share on other sites More sharing options...
EVLXX Posted June 14, 2008 Share Posted June 14, 2008 For 1. 2 Db's is huge to the ear.... Db's work like the Ricter Scale... it's multiples higher for each number value. Secondly... It's not the size restriction that really hurt you with the Db Killer it's the shape.... Basicall it's restricting the flow by 25-30%.... very bad design there. Quote Link to comment Share on other sites More sharing options...
R1000 Posted June 14, 2008 Author Share Posted June 14, 2008 Only a ~2 db difference, is it worth the HP loss ? Will it pass for MOT or is more reduction needed ? It will pass MOT, the requirement is 103 dBA maximum. No it is definitely not worth the power loss for normal driving. 2 dB is so little that the ear baerly notes the difference. Quote Link to comment Share on other sites More sharing options...
R1000 Posted June 14, 2008 Author Share Posted June 14, 2008 For 1. 2 Db's is huge to the ear.... Db's work like the Ricter Scale... it's multiples higher for each number value. Secondly... It's not the size restriction that really hurt you with the Db Killer it's the shape.... Basicall it's restricting the flow by 25-30%.... very bad design there. It do restrict flow for sure. Any suggestion for how a good design would be? A dB killer that attenuate noise effectively and is not very restrictive? 2 dB is a very little difference to the ear. It is almost the double power (3 dB is double), but the ear needs a change of 10 dB to recognize it as X2 or X1/2. Quote Link to comment Share on other sites More sharing options...
TOXXIC Posted June 15, 2008 Share Posted June 15, 2008 Cool video, but I really, REALLY like your frame plugs! Where did you get them? Quote Link to comment Share on other sites More sharing options...
EVLXX Posted June 15, 2008 Share Posted June 15, 2008 For 1. 2 Db's is huge to the ear.... Db's work like the Ricter Scale... it's multiples higher for each number value. Secondly... It's not the size restriction that really hurt you with the Db Killer it's the shape.... Basicall it's restricting the flow by 25-30%.... very bad design there. It do restrict flow for sure. Any suggestion for how a good design would be? A dB killer that attenuate noise effectively and is not very restrictive? 2 dB is a very little difference to the ear. It is almost the double power (3 dB is double), but the ear needs a change of 10 dB to recognize it as X2 or X1/2. Yes.... but I can't tell you.... because then I would have to KEEL U ! ... sorry... I really wish I could tell you, but I can't let out all my secrets..... ... so for now I'd suggest you just live with it.... ... Why do you need it quieter.... again ? MOT...... what's that ? Quote Link to comment Share on other sites More sharing options...
Keith Posted June 16, 2008 Share Posted June 16, 2008 Cool video, but I really, REALLY like your frame plugs! Where did you get them? I have the same, or very similar, frame plugs, only mine are polished aluminum. I got them from a guy on Ebay a number of years ago. I haven't seen them on there in a long time. They were pretty spendy, IIRC, something like $50 or so. Quote Link to comment Share on other sites More sharing options...
R1000 Posted June 16, 2008 Author Share Posted June 16, 2008 Cool video, but I really, REALLY like your frame plugs! Where did you get them? The frame plugs were one the bike when I bought it, and the swingarm bobins are from a local shop. Quote Link to comment Share on other sites More sharing options...
CxBXR Posted June 16, 2008 Share Posted June 16, 2008 Any suggestion for how a good design would be? A dB killer that attenuate noise effectively and is not very restrictive? Reduces noise levels up to 10dB's with just an insert Remove the BARK not the BITE! (***clipped from sales add I am in no way supporting their product's just came accross their site & have no idea if it really works as they claim) http://www.dirtwerkz.com/Merchant2/merchan...tegory_Code=260 Quote Link to comment Share on other sites More sharing options...
R1000 Posted June 16, 2008 Author Share Posted June 16, 2008 Any suggestion for how a good design would be? A dB killer that attenuate noise effectively and is not very restrictive? Reduces noise levels up to 10dB's with just an insert Remove the BARK not the BITE! (***clipped from sales add I am in no way supporting their product's just came accross their site & have no idea if it really works as they claim) http://www.dirtwerkz.com/Merchant2/merchan...tegory_Code=260 Thanks, a real nice design on that dB-killer. I guess it may reduce noise as the say by up to 10 dB (half volume to human ear). The inner diameter is only about 50%, which reduces the area to 25%. How they could claim this will not eat hp is a bit of a mystery though... The roof at the end hinders direct pulses to propagate directly to the outlet. Perhaps a larger ID and the use of a roof as they do, would give a better balance between sound and power reduction. I'll pass MOT with my dB-killer with a margin of almost 3 dB and will leave it as is, but the roof design appears to be a clever idea. Quote Link to comment Share on other sites More sharing options...
Para045 Posted June 17, 2008 Share Posted June 17, 2008 MOT...... what's that ? MOT Test, I would assume it is the same as in the UK and to a certain degree on the East Coast of Aus where every year before renewing the registration for the vehicle it needs a "roadworthy" certificate :icon_think: Quote Link to comment Share on other sites More sharing options...
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