Dunstall replicas silencers

Classic Norton Commando Motorcycles.

Dunstall replicas silencers

Postby tigman88 » Sun Jan 22, 2012 4:24 pm

Hi, I really want to put a set of those replica Dunstalls on. How much different do they sound compared to the regular peas> Also I have A VM38 Mikuni on Its jetted really well.. Will I have to mess with it??? :idea:

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Re: Dunstall replicas silencers

Postby mikie3117 » Sun Jan 22, 2012 10:31 pm

Hi. I have a nice set of those but they are 1" & 1/2 vice 3/8th. The sound is very quiet compared to the standard pea shooters. I would run them but don't like the way the adapters fit. You should do some plug checks and may have to change jetting.
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Re: Dunstall replicas silencers

Postby tigman88 » Mon Jan 23, 2012 8:47 pm

alright thanks for the tip

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Re: Dunstall replicas silencers

Postby Bruce MacGregor » Tue Jan 24, 2012 7:08 am

I have ones that were from "Coventery Spares" about 7 yeaes ago. Very nicely finished and near exact copies with out the Dunstal logos. But they had a metal blank in the center pipe that was way to restrictive. I used A large hammer and a 1 inch dia pipe to knock it out. They ran much better and sounded better. So make sure you can see right through them like the originals!
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Re: Dunstall replicas silencers

Postby debby » Tue Jan 24, 2012 7:48 am

I have a pair of the EMGO Dunstall replicas. I got them really cheap, $80 for the pair brand new in the box. They're a little quieter than the Wassell peashooters but not much. No jetting changes were needed on mine. Maybe they vary. Another friend has a set that are a lot louder and he claims not to have hacked the baffles.

The inlet is too big for standard 1-3/8 inch Norton headers so they come with reducers. The reducers are still a pretty sloppy fit so I had to cut up a Coke can to make shims. They have the same universal mounting channel as the Dunstalls did, but they didn't get that quite right either. On the original Dunstalls, the bolts slip into the channel head-first and the channel is just the right width to keep the bolt from turning, so you can easily install the Norton mounting plates and tighten the nuts down. On the EMGOs, the channel is too wide to keep the bolt from turning, which makes it difficult to tighten the nuts. Seems like there is always something like that on pattern parts that is "off" because the people making the copy didn't understand the function.

Otherwise they seem ok. Chrome looks good.

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Re: Dunstall replicas silencers

Postby Robert_Norton » Tue Jan 24, 2012 11:48 am

I purchased a pair of the Emgo megaphone mufflers a few years ago, and they were packed with fiberglass-type packing around the long perforated tube that runs down the middle. There is also a perforated cross section within the long perforated tube. Contrary to what another member has indicated in this thread, I've never seen a Dunstall megaphone muffler that was straight through with no baffling. Maybe some of the shorty-style ones that came later on, but in the style similar to what Emgo is making, the mufflers I've seen have always had a perforated tube down the middle.

I run my 850 with Dunstall mufflers that have had the baffles sawed off, so they're just empty megaphones with the gattling gun style cap mounted on the end, and they are much louder than any pea-shooter style mufflers I've ever heard, and I think they sound a lot better. And when I say louder, I mean WAY louder. It's definitely not something to do unless you want your bike to be outside and well beyond what normal societal expectations are for what motorcycles are allowed to sound like. But it's a good loud, and for me it's the only way to go.

I've also run Nortons with unaltered Dunstalls, with the glass packing removed, and that provides a very throaty sound, and I think at least as loud as pea-shooters. And that's without having knocked out the perpendicular deflection disc that's in the middle of the long perforated tube. I've never run a set of them having done that.

And size does matter, too. The earliest Dunstalls were a smaller diameter than the mid-period type (like the one's Emgo makes now), and the exhaust tone was very much perceptibly higher. Beautiful in it's own right, but not as deep as the larger-bodied mid-period type -- which is what Emgo is similar to.


I once looked down one of the p-shooter mufflers that Kenny Dreer put on his bike, and they were just hollow with no baffling, no louvring, nothing. There's a member here selling one, and if you check his video you can get a sense of how gnarly an empty pea-shooter sounds. If you look in the for sale forum here, or on eBay, you can find the video link to the seller video for the Dreer bike that's currently for sale.

For stopping the head of the bolt from turning within the mounting bracket, I use a long thin screwdriver with a flat blade. When things start to get tight I just pulled it out and by that time the bolt was grabbing.


You should use ear protection when you're riding, too. I think the wind noise alone, from it whistling around through the helmet, is enough to damage your hearing.

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Re: Dunstall replicas silencers

Postby hobot » Tue Jan 24, 2012 12:11 pm

I snagged a pair of long dong Dunstalls 6-7 yr ago and these had inner tube w/o packing left and a perforated screen at narrow end then a 6 tube baffle with a soup can over their ends so exhaust exited the tube ends turns back on itself in the can cap then back out the ring slot between can and mega end. Throaty sound but not much louder than open peashooter. With end baffle removed you will be hunted down to shoot for the LOUDness EAR damaging noise unless barely on throttle. An open empty Dunstall can out LOUD Harley open headers. Empty Dunstall long dong only weight like 6 lb.

When I ran w/o any baffle my hopped up Combat would fall on its face to idle and putt putt around, seriously bogging if not reving a bit to get moving and then serious bog to increase throttle unless already in low mid range, Sucked big time and didn't help much on top end. Best solution was an end plate with a 2"-hole in center, then got low end deep base not response back and top end too with exhaust jets going straight through and out ~8 inches w/o the ripping ears out megaphone piercing sound - just a nice loud dragster Roar.

The inner tube and packing adds like 3-4 lb mass to bounce on the rubbers and haul around too. The Ego's mega's I've heard and felt at rallys sounded fine but lack the peahooter puff ball vortexes, just blows back in pules.

If I destroy my Dunstall then next up will be the Emgo's empty but for end cap wtih header size hole in it.

There was a fella on Brit Iron list that examined all the peashooter inner tube louvers to find 3 types, each with a distinct sound, the best was factory the had chevron shaped louvers, then the cresent shaped and then the straight cut kind.
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Re: Dunstall replicas silencers

Postby Robert_Norton » Tue Jan 24, 2012 12:44 pm

hobot wrote:I snagged a pair of long dong Dunstalls 6-7 yr ago and these had inner tube w/o packing left and a perforated screen at narrow end then a 6 tube baffle with a soup can over their ends so exhaust exited the tube ends turns back on itself in the can cap then back out the ring slot between can and mega end. Throaty sound but not much louder than open peashooter. With end baffle removed you will be hunted down to shoot for the LOUDness EAR damaging noise unless barely on throttle. An open empty Dunstall can out LOUD Harley open headers.



Just to be clear here, I don't run them without the six-holed cap on the end. I saw off the long perforated tube that runs down the center, so the megaphone is empty, but still retains the end piece with the six or seven pieces of pipe welded together. Then you're okay up to about 3000 rpm's, and after that all hell breaks loose in the volume department.

And I am familiar with the baffling plate that came with various styles, including the long ones you're using. I do not use that plate, although a bike my brother had did have the 27 inch Dunstalls, with the same baffling plate that's centrally mounted on the end cap.

For anyone reading this that's trying to decipher what the hell is being discussed, Emgo mufflers are not of the same design and do not come with the centrally mounted end-cap that only some Dunstalls were sold with.

As far as the sound escaping from the smaller pipes that comprise the end of Dunstall pipe, I do not possess the knowledge of physics to comment knowledgeably regarding exactly what is occurring.

I can comment from direct experience, though, and say that in my opinion a Norton with gutted Dunstalls sounds way better than a Harley with straight pipes, especially when de-accelerating from higher RPM's, and very likely could be louder. I think by it's very nature, a megaphone is going to amplify a sound more than a straight pipe.

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Re: Dunstall replicas silencers

Postby Bruce MacGregor » Tue Jan 24, 2012 1:09 pm

The original Dunstall patented "Desibel Silencers" Pat # 1063409, Quote Dunstall Catalog,
" This new straight through absorption type dunstall Silencer has an integeral sound diffuser to cut down on noise output with out loss of performance".

Dunstall's had a straight through perforated tube wrapped in fiberglas that exited into the diffuser chamber.
The Coventery Spares version had a solid steel blank tack welded inside the fiberglas wrapped perforated tube that forced the exhaust out through 1/2 of the perforated tube holes then back into the remaining perforated tube before exiting through the diffuser. My 850 knew right away something was wrong. Once the blanks were knocked out the bike ran fine!
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Re: Dunstall replicas silencers

Postby hobot » Tue Jan 24, 2012 7:03 pm

Ah Robert and Bruce, makes my Amals bowls warm on the descriptions.

A proper megaphones sloped interior is to help spread it sonic reflexion wave over big band pass than its length alone centers on, which should match the exht valve still open as the low pressure front hits.

Peel set back a TV film crew on their heels by pure shock reflex at Bikes Blues BBQ on a series they were doing on the excessive noise of all the big twins and no big twin handy at the time. So yes Sir its documented a hi compression lightened crank 2-1 dialed in long dong MegaPhone can out BLATTT most big twins.

I owe my 1/2 reputation as braggart on finally getting that Dunstall right and wrote it up years ago titled ***MEGAPHONITIS!!!*** "-Itis" is a sufix that means, Inflamed, Inflamed means Red, Hot, Swollen and Painful! I will never forget that first ride out my drive way - I about got flat left behind on just mere partial throttle ups. The other half is d/t a rump rod which gave even more G's!

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Re: Dunstall replicas silencers

Postby Stephen Hill » Tue Jan 24, 2012 10:52 pm

My 1972 Combat came fitted with 1 and 1/2 inch headers and original Dunstalls (the shorter version, with the reverse cone tip, kind of like a large diameter peashooter). I found them annoying loud. They tended to blat, rather than rumble, on low throttle. Sounded cool when you wrang its neck though. I replaced them with peashooters cause I preferred the stock Norton sound.

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Re: Dunstall replicas silencers

Postby tigman88 » Wed Jan 25, 2012 2:38 pm

Hey I bought a set yesterday from Motorcycle superstore. In today awesome ..........If possible could I see how some of you guys mounted them(pics) would be grateful...

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Re: Dunstall replicas silencers

Postby hobot » Wed Jan 25, 2012 2:53 pm

Yes for real life on real Commando I vote peashooters. The mega's need modifications of motor items and life style to be desirable. Still Peel special needs the megaphone and I know I'm going tear it up someday so want to see and hear how the emgo works out. Took me some mental evolution to realize one half an exhaust system weighs less than duals, duh. Here's some u-tube sonics of emgo's shorties and Dunstall types. Not bad.

http://www.youtube.com/watch?v=Vgi5IKtBu_s
http://www.youtube.com/watch?v=5iGFIaGw ... re=related
http://www.youtube.com/watch?v=EvsMpGQ0uhA
http://www.youtube.com/watch?v=0ECqmTpbCSU
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