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Any ideas on making my shorty GP quieter?

2.1K views 18 replies 5 participants last post by  MilwDave  
#1 ·
I just bought the shorty GP from radiant cycles and also purchased their little quiet baffles. I haven't installed them yet but pretty sure it's going to be too loud. Has anyone had success with rigging up a third party baffle with fiberglass? Would love to know how you did it and what parts you used.

Thanks!
 
#2 ·
I also have the GP shorty’s and agree…they are loud Out of the box

i simply fitted a 42mm universal baffle to each one, tightly wrapped in fibre glass baffle wrap. Problem solved. I still get the nice look of the shorty’s and enough of the bark to keep me happy but it doesn’t upset my neighbours, or my ears nearly as much!

I bolted them in (from the outside but only because I like the more “industrial look”…could just as easily bolted from the inside)


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a very cheap solution (less than £20j to the issue

https://www.google.com/url?sa=t&rct...le-Exhaust-Silencer/dp/B08HH8DF4V&usg=AOvVaw0XeyjevG5ZvFqUxM-ku5vq&opi=89978449
 
#3 ·
Thank you! I just bought a couple of 42mm baffles and will wrap them in fiberglass. I bought some aftermarket baffles prior that said it was made for the GP shorty but it didn't fit. Hopefully these new baffles will work better. Have you recorded your decibels?
 
#4 ·
Yes I did. straight through pipe was 98 at idle and peak at about 104! Ouch

just the GP’s was about 95
GP’s with baffles and wadding is now about 80 at idle and 89 peak. UK law is 89 to pass the roadworthy test so I’m perfect!
 
#8 ·
So I just installed some universal 42mm baffles and wrapped them with fiberglass. The issue is when I first turned it on, it wouldn't start. Tried again and then after the 5th time it started. But now at idle there is black smoke coming out. It's definitely running richer because has a strong gasoline smell that wasn't there before. Do you think it's too restrictive with that end cap left on the narrow end of the baffle? Should I remove it? Thanks!
 
#5 ·
Whilst your levels are correct I have never had it measured and the rule below is a cut and paste from the Gov.uk guidelines for MOTs. If they deem it too loud do they measure it?


If possible, you should assess the exhaust noise by revving the engine to approximately half the maximum engine speed. The engine should be warm before you carry out this check.
It is not possible to rev the engine on twist and go type motorcycles.
The exhaust system and silencer should be in such condition, or of such a type, that the noise emitted from the motorcycle is not clearly unreasonably above the level expected from a similar motorcycle with a standard silencer in average condition.
 
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#6 ·
Agreed. My old harley had Vance and Hines pipes on it and , whist it never failed an MOT, it nearly always came with an “advisory notice” saying “noisy exhaust” :) There was never a number on the advisory and it and it never failed but the MOT tester often gave me the dB readouts he took, either out of interest or in case I was ever stopped by the police…or maybe he just didn’t like noisy bikes 😀.

I think most decent MOT testers take a common sense approach to this stuff and the key line always seems to be “the noise emitted from the motorcycle is not clearly unreasonably above the level expected from a similar motorcycle with a standard silencer in average condition.”. My tester always seemed to reasonably compare my old Harley to “other noisy American bikes”, and not to, say, an R1 or a BMW GS etc

Of course, maybe the local police would take a different view on a different day, hence I always like to know the numbers just in case 😀

Having said that, I”m old and sensible now and i havent been stopped for years and even when I was young and stupid, the police have never tested decibels by the roadside….but then again, they never use to test window tints (or visor tints?) until they all got those fancy light tester/s…so who knows what new toys they get next 😀

To me it’s a simple equation, don’t give them a reason to pull you over and all will be good 😊 (until the new UK roadside cameras start to roll out that detect noise limits on top of everything else…then we are in trouble. Why UK Noise Cameras are a Good Idea but Also a Bad Idea | Stable Blog.)
 
#7 ·
To me it’s a simple equation, don’t give them a reason to pull you over and all will be good 😊 (until the new UK roadside cameras start to roll out that detect noise limits on top of everything else…then we are in trouble. Why UK Noise Cameras are a Good Idea but Also a Bad Idea | Stable Blog.)
They were trialling the noise cameras in my area. The best option at a price of course is opt for a system that has already got all the relevant approvals and will keep you on the side of legality. Also switchable by the press of a button or will adjust accordingly dependent on gear, speed and throttle position. Penzl, Miller and Jekill and Hyde all do exactly what they say on the tin, literally!
 
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#9 ·
So I just installed some universal 42mm baffles and wrapped them with fiberglass. The issue is when I first turned it on, it wouldn't start. Tried again and then after the 5th time it started. But now at idle there is black smoke coming out. It's definitely running richer because has a strong gasoline smell that wasn't there before. Do you think it's too restrictive with that end cap left on the narrow end of the baffle? Should I remove it? Thanks!
 
#10 ·
That doesn't sound good! I got a tiny amount of (grey) smoke on first start up but I think that was just sone loose wadding burning off I think... It's been perfect since. And I left the caps on. No issues firing up at all. Back pressure issue? To much wadding blocking the flow?

I'm no engineer or mechanic but maybe it's the wadding you used? I used specifically titled "exhaust wadding wrap " from amazon.. No idea how similar that is to the wadding you used?

Perhaps someone more mechanical can opine on this?
 
#12 ·
Can’t seem to find any 42mm “short honeycomb“ ones that you mention, over here in the uk. So I’m probably looking for the “wrong thing”?

do you have a link to any such baffles that fit (other than the ones Radiant sell of course :)…though perhaps I should just get those. My issue is they don’t seem to sell them in the UK and postage is twice the price of the baffles themselves! 😂 ) so I can refine my search?

I am assuming these honeycomb ones go into the slip ins the same way that the universal baffles do? )Ive here in the uk that are anything but the old school type I’m using (metal tube with holes in etc).

always keen to try new options to see what they do to the sound (and potentially even power delivery - though not much without replacing the headers I suspect)
 
#13 ·
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#16 ·
If you can use only 4”, cut one in half!
Charlie
 
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