Muffling Monty

LaverdaIan

LaverdaIan

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With a return to Lakeside coming up it seems that I will have to change the tailpipe on Monty to get under their 95db regulation. I haven't measured current pipe but would guess I'd be about 105db or so with the straight through 2-1 stubby I've got on now.
Spoken to Pete Gray at Pipemasters who informs he can knock up the pipe for me.. (he was also keen to know about the Stranglers revival and will be there as well now..it's gonna be a big day.. ;)

Question is: what will be the result of restricting the exhaust in this way.. will rejetting or a change of gearing be required..? Rumour is that you lose a lot of power, but others suggest it just moves the top of the peak power a little (or a lot)..
Ideas anyone..? and thanks.

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How's this for an idea?

I used to do a bit of accoustic and vibration isolation engineering in a previous life. I still have a sound level meter somewhere. I could volunteer to do the noise level checks at Lakeside if someone were to pay my travel expenses. When checking your Monty, I might just forget to take the plastic cover off the microphone end of the meter. Not that I'd ever suggest any foul play - it's just that I can be a bit forgetful sometimes, especially if well lubricated with single malt ...  :D
 
Bloody good plan Cam, I like your attitude.. :P

Unfortunately, the powers that be have installed sound meters ON THE STRAIGHT.. so we must toe the line if we are to play.. mind you, I am inspired.. heavy plastic bags and cable ties perhaps.. :LOL:

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In the absence of any science you might have to do a bit of trial and error.....
Got time for that??
What about using a used termi muffler or something with some packing and knocking up an adaptor.
Keep the cost down.
 
Ian,
It's nigh on impossible to predict how your motor will behave until you fit the pipe and see how it goes. 95db is a very restrictive upper noise limit but it shouldn't necessarily restrict power [just look at the outputs on road legal bikes nowadays], the problem is achieving 95db through an exhaust which will fit into the limited space available.
Gearing will probably remain the same- unless the bike is strangled to such a degree it won't pull peak rpm. Re-jetting will almost certainly be  required to match the characteristics of the new system and a dyno will save you a lot of time and messing about, assuming the dyno guy knows his onions and you have a suitable quantity  of jets to work with. If not you might as well do trial and error stuff on your local roads, works for me... 
 
supertrapp mufflers,show and go in Adelade has them with discriptions and pics on there website.They have been around for years.You would have seen them on dozens of race bikes.A day on the Dyno jetting for power and then playing with the muffler discs to adjust for sound.
 
We've been running to tight noise regs in NZ for years now. Supertrapp, yes, can work well. $$$...
Most of the stuff I build uses a straight through style of muffler. Perf tube internal with plenty of can volume.
From experience with similar size twins i'd run 1 7/8 or 2 in core dia by say, 400mm long and around 100mm OD.

If you are running a 2 into 1 short system, I wouldn't be at all surprised to pick up a bit at the top end with a muffler added...seen it before.

Couple of years back we had a bunch of Can-Am cars running at Levels circuit - limit 92Db....Gloriously over the limit except for the bit by the meter where everyone idled past.....hilarious.
 
Cool, thanks guys. Have a fair selection of jets Bob, so we'll (hopefully) soon sort it. As you say, once I'm on the bike I'll know a lot more.
Pipemasters have been making specialised pipes in Brisvegas for over 25 years now, in fact Pete Gray made Monty's current set-up back in the day when the original owner was working for them. I reckon he'll be right to create the unit I need.
And yes, could try to squib it, idling down the straight, but what's the point of that if means that I'm sent for an early shower..

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I used to have a Honda 4 with a 4-1 exhaust and a reverse cone megaphone. It had no baffling at all, just the empty megaphone. At a local track day, the noise boys told me it was too loud and I wouldn't be permitted to run it like that. So I scrounged in a rubbish bin for a beer can (which would just fit through the opening in the end) punched a bunch of holes all over it with a sharpened screwdriver, then jammed it into the megaphone using a broom handle as a rammer. It worked quite well as a baffle and stayed put long enough to satisfy the noise scrutineers. It self-jettisoned on the first full throttle blast down the straight. Good thing there wasn't another rider behind me when it shot out. By that time the noise testers had packed up and gone home so it wasn't a problem.

 
LaverdaIan said:
Pipemasters have been making specialised pipes in Brisvegas for over 25 years now, in fact Pete Gray made Monty's current set-up back in the day when the original owner was
Click to expand...

And he's a sponsor of the Concours this year, which reminds me I have to take the new posters and flyers up this morning. He's moved his workshop just up the road from my place. If he has it ready by tomorrow arvo I can bring it to the meeting Ian, or Concours if it's a bit later.
 
Hey, thanks Drikko, but he hasn't started yet. Needs my current one to set up the jig, and it is firmly attached to the bike this week. CeeJay arrives tomorrow and we test the new front end on Monty at Warwick on Thursday.. :P

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One trick people use here is to have the outlet aiming as high as practicable so that the pulses are aimed at the sky.
As Greg says, a high volume cannister with straight through perforated tube tightly packed with fibre-glass should see you right and "should" not require the jetting changes of a restrictive system. 95db is a mean target though, I would have thought an Alpino on std mufflers would struggle with that. Pass the noise meter on the opposite side of the track.
 
One of my last 500 kawasaki twins was dyno developed with a straight pipe (no muffler) When the neighbours complained, we figured we had better add a muffler. Picked up around 5 hp when we added one. 79hp on straight meth, at the wheel.

Similar to a monty in that it was a 500 twin - 8 valve - 180 deg crank. Revved to 13 though.....

For what it may be worth - Primaries 26inch X 1 5/8in OD - Secondary, 24inch of 2inch OD. Muffler added, as quoted previously 400mm long, 2in perf pipe core, 100mm OD. Easily made the then limit locally of 95Db ridepast measurement.
 
Hmmmm, very cool. Thanks Greg, I am really trying to get my head around this change to my bike.. I reckon that we will find out what the bike needs to be "vewy vewy quiet" and still be a neat bike bike to ride at places like Lakeside. As it is just 15 minutes from home I'm keen.. ;)

Monty may end up working hard Lee, but we'll give it a crack.. :P anything for a lap or few around our old backyard.. as many blokes that I talk to about returning to Lakeside, they are to a man, keen to be there, or recall some brilliant times at a challenging little circuit...

Let the good times rollll... :P :LOL:

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I've seen some of the classic club guys using an extra absorption can spring hooked onto the back of their megas for some of the more sensitive country runs and MOT time.
Not sure if it's a readily available part or just a style they have copied.
 
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