peashooters

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oldmikew

oldmikew

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Does anyone know anything about their development? was the reverse cone an afterthought .. any gain apart from decibels in cutting them off?
 
Seems reverse cone pea-shooters were about unique to Commands. The earliest/originals reverse cone silencers had a small restriction washer at the silencer outlet tip, this produced a unique whistler type sound when the throttle was backed off. Also nick picking researchers for original issue sound/feel, discovered the originals had curved/moon crescent shaped flutes, while all others afterwards have squared off or shallow straight edge triangular flutes.

My 1st Combat with original pea shooters had reputation that proceeded me so on 1st time invited to ride with the group said they knew it was a Norton twin from several miles away. Alas rust destroyed to fall off.
 
hobot : I did not know about the whistle.. had a goldstar silencer on my super rocket and that whistled.. my commando came with triangular flutes and a little canvas bag with two restrictor washers , a couple of self tappers and a couple of main jets . i think 200 or 220.. Never fitted.
The silencers on mine are getting a bit tatty so was thinking of replacing for road use.. there are a couple of hill climbing events in the UK that have NO NOISE restrictions ! so with the ends cut off and sprayed matt black they would look wicked .. More power or torque is a different issue... More noise certainly...but
looking at them , I would have said someone picked up a pair of megaphones that were to hand ..and then welded on the reverse cones as an afterthought... The Brits of that era did their Rand D on a suck it and see basis.. The Matchless
production racer had tapered megaphones perhaps there were a pair knocking around in Plumpstead which gave the basis
 
oldmikew said:
hobot : I did not know about the whistle.. had a goldstar silencer on my super rocket and that whistled.. my commando came with triangular flutes and a little canvas bag with two restrictor washers , a couple of self tappers and a couple of main jets . i think 200 or 220.. Never fitted.
The silencers on mine are getting a bit tatty so was thinking of replacing for road use.. there are a couple of hill climbing events in the UK that have NO NOISE restrictions ! so with the ends cut off and sprayed matt black they would look wicked .. More power or torque is a different issue... More noise certainly...but
looking at them , I would have said someone picked up a pair of megaphones that were to hand ..and then welded on the reverse cones as an afterthought... The Brits of that era did their Rand D on a suck it and see basis.. The Matchless
production racer had tapered megaphones perhaps there were a pair knocking around in Plumpstead which gave the basis
Click to expand...
Regarding the Twitter from a commando , my 750 gives out a healthy goldstar sounding Twitter when I have a a gunson colourtune fitted,I've always wondered why it does that??
 
Mike, they’re not really reverse come Mega’s as they have a straight through perforated (of various different designs) tube inside them. Therefore, in effect, they are really just absorption silencers, as fitted to many old Brits.
 
NEEDING POWER? by Owen Greenfield
Published on Apr 26, 2017
The inner perforated tube was removed when the original welds cracked away. The measured length header pipe now protrudes well into the expansion cone for pulse generation. The exit cone acts to re-compress the gases just prior to expulsion through the removable baffle adaptation
Click to expand...

 
As I understand exhaust system design, The size of the pipe, the volume of the muffler and each change in diameter along the path affects how the system performs with a given engine/cam/carb/rpm combo. Where the pipe joins the muffler and at the two diameter changes at the end of the peashooter reflects a negative pressure wave back to the exhaust valve and the proper timing (length) of these changes is what helps extract subsequent exhaust pulses. The presence of baffles in the muffler tends to negate some of this effect, and if it's a packed perf-pipe design, the volume of the meg is moot, so a straight-though (LOUD!) design is most efficient. I remember reading Manx Norton tuners could vary the powerband just by slipping the meg forward or back on the pipe, changing the total length and timing of the reverse cone's 2 negative pressure pulses. And we all know intake length works the same way, only with a sonic-speed positive pulse racing back to the velocity stack end and creating a negative that helps suck in the next charge.
 
Proper megaphones usually work best in one part of the rev range (which on a racer, would normally of course be the very top end).

The ‘payment’ for this that they work less well in the other rev ranges. They can in fact work very badly and cause all sorts of 8 stroking / misfiring / flat spots / etc. Otherwise known as ‘megaphone itis’.

Therefore, playing with real open megaphones on your bike is a task not to be taken lightly, you will definitely get more noise, definitely some point in the range with ‘megaphone itis’ and possibly no upside unless you put experimentation time in!

The reverse cone part of an open mega goes a long way to reducing megaphone itis. But it’s still an issue.

A straight through pipe, with straight through absorption silencer is MUCH more forgiving.
 
Here's some pictures of the inside of my original 69 (production date 'S'). I lit it with a small bulb on a wire. The first 2 pics are from the rear, the first is a view from the outside where you can see the baffle which is right at the widest part of the silencer. That strap goes from one side of the outside to the other and holds the center tube and the baffle. The second picture is looking at the inside of the rear and is a bit deceiving. The round lighted area is the inside of the silencer, the part that goes from the header to the widest part, the short narrowing part is mostly not visible because of where the camera is. You can see the light bulb at the bottom and some cobwebs at the right. The forth picture is of the flutes from the input side. And third a hand drawing of what I perceive the inside to look like without tearing it apart.

peashooters
peashooters
peashooters
peashooters
 
Nothing between my head & the exit from the pipes but air (just like 84ok's) so they sound the same, maybe I don't ride hard enough to experience megaphonitis, but I just love the noise & so do my neighbours ;-)
 
diff hole size, old vs new = ~"more racket" ?!


op
oldmikew said:
Does anyone know anything about their development? was the reverse cone an afterthought .. any gain apart from decibels in cutting them off?
Click to expand...
 
Dogt has example of last of famous factory issue, tweetering drilled end plate with curved crescent louvers. Peashooter - reverse cones are just sleek glass pack 'cherry bomb' straight through mufflers with a end plate or open end - unless gutting or rust allows blowing full open then sound amplifier bull horn. Nothing seems to put out the distinct far traveling puff ball vortexes like Peashooters, far as I know so far. Try a decent ride with mufflers removed to sense 12 lb less mass if not the better breathing thrust. A real megaphone is tricky thing to make work but boy howdy once it does ya'll know reason they were introduced on vintage cycles. Mz Peels will be able to slide more/less on the collector pipe so good to know in past it was detectable effect.
 
DogT thanks for posting the photos and the drawing . I had assumed that if If I cut off the end cones then would be able to get the triangular baffles out. Well may be not .

Nigel thanks for reminding me about the efficacy of open pipes ,that peashooters are actually a sound absorbtion
silencer and getting a good megaphone outcome is a bit of a black art.

Danno Thank you for reminding me just how complex a matter it is to get an exhaust right

Mike Sullivan Noise - a major contribution to road safety at least if you are on a bike. they may not see but they hear you coming..

84ck - liked the video perhaps something along those lines might work..

Ok the thing is I am going to replace the originals with like for like for road use, as for the rest i will have a couple of peashooters to play with.. hate to throw away and would sooner recycle for bike use than see them come back tome as baked beancans or whatever it is they make in China these days. I will have to see how it goes

I did once try a little experiment and made up plates so i could slide the peashooters along the pipes.. Neither shortening nor lengthening the distance from the reverse cone end to the exhaust port made any benificial difference, both were much worse!
 
I was a draftsman at NV late 69 to late 70. I drew a so called "peashooter" silencer, and was peripherally involved in their development/testing. The silencer that I drew, had a tube running front to back, with three rows of pierced flutes, around that was wrapped some expanded metal, spot welded in place. On assembly something like 17 to 19 ounces of fibreglass wool was packed between the full length fluted tube and the external parts. It was then all welded together, cleaned up, polished and plated. The little insert piece, secured by a self tapper, was to get the noise down to comply with the incoming noise regs in California. Even with the insert in place you could see all the way through. The noise testing and development took several months, and involved riding past a noise meter at (very) specific speeds and in specific gears. The testing was done at an old WW2 air base, where there was lots of open space, as reflected noise from any buildings, trees, people, small furry animals could really upset things.
Of course the central fluted tube could rust out and blow out the back, rapidly followed by the fibreglass wool, at this stage they sounded superb but were probably not compliant with Californian regs!! I had a pair on my Honda 500/4, and once the insides had disappeared they really did sound magic.
cheers
wakeup
 
I have a pair of peashooters on my Triumph t140. I was suprised how different it sounds to the Norton. More of a bass note compared to a higher pitch sound on the Commando. Must be down to the different cams and cylinder head design, both being 360 degree twins. I also have a set on my Trident. The howl will make the hair on the back of your neck stand up when you get above 6 grand.
 
you were the one that came up with the reverse cone part?

this pix came up in the thread & not clear on?
so called "peashooter"
Click to expand...
peashooters


wakeup said:
I was a draftsman at NV late 69 to late 70. I drew a so called "peashooter" silencer, and was peripherally involved in their development/testing. The silencer that I drew, had a tube running front to back, with three rows of pierced flutes, around that was wrapped some expanded metal, spot welded in place. On assembly something like 17 to 19 ounces of fibreglass wool was packed between the full length fluted tube and the external parts. It was then all welded together, cleaned up, polished and plated. The little insert piece, secured by a self tapper, was to get the noise down to comply with the incoming noise regs in California. Even with the insert in place you could see all the way through. The noise testing and development took several months, and involved riding past a noise meter at (very) specific speeds and in specific gears. The testing was done at an old WW2 air base, where there was lots of open space, as reflected noise from any buildings, trees, people, small furry animals could really upset things.
Of course the central fluted tube could rust out and blow out the back, rapidly followed by the fibreglass wool, at this stage they sounded superb but were probably not compliant with Californian regs!! I had a pair on my Honda 500/4, and once the insides had disappeared they really did sound magic.
cheers
wakeup
Click to expand...
 
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