Dunstall Replicas - 1971 OIF T120R

[NM Bonny]

Removable baffles , never heard of such a thing in those days.

Ah, okay. Sounds about right.

Well, anyway, I'm glad they have them these days for experimentation purposes. BTW the 'red cap' Dunstall megaton megaphone style in the initial post has a seamless, rounded aft end combined with a removable baffle. It's 25" overall, a little bit shorter than the EMGO version, but nearly identical to the length of the OEM cans. So, this may end up being my choice for the trials...

 

[solomon]

Solomon: what is the O.D. of the Dunstall replicas, if you don't mind?

That's not wee. It's green tea.

The original Dunstall had a very distinctive sound on the overrun. I suspect the replicas don’t, looking at the tail end of these pipes.

Just tried from 4,000 revs. Niente. Nichts. Nothing. Probably an engineering success, a hooligan failure?

Does burble nicely going down hill slowly, little or no throttle, low revs.

 

[NM Bonny]

Update: I got a response to my email about the lovely seamless Red Cap Dunstalls with removable baffles that I linked to above, which the website says are out of stock. They are indeed available for 88 BPS, or $109 US. I've ordered a pair.

Only thing is, the inlet accommodates 1-5/8 to 1-3/4" header pipes, and my OEM header pipe flares to 1-1/2" where the OEM mufflers clamp on. So, I'll have to ask the machinist who makes my parts for Creative Spridgets (and who lives just down the road) to jump on the lathe and turn some adapter sleeves. But I think it'll be worth it, as these mufflers are really nice looking.

However, once they're fitted, the header pipes will look more tarnished and worn... and I'll end up buying new pipes, too.

 

[NM Bonny]

Error: I had been looking at the wrong page. They offer these in two sizes, one of which is 1-3/8 to 1-1/2", which I need: BBBUN2 is the correct part number for the '71 OIF T120R. No extra machining... yay!

 

[solomon]

Error: I had been looking at the wrong page. They offer these in two sizes, one of which is 1-3/8 to 1-1/2", which I need: BBBUN2 is the correct part number for the '71 OIF T120R. No extra machining... yay!

They are very nice. I'd seen those, but only prised my wallet open enough for the used ones I bought.
Look forward to your reporting

 

[solomon]

 

[NM Bonny]

View attachment 55915

Oh, neat, thanks for posting this. Indeed, the radius in the drawing at the outlet end seems to reflect what Bloodknot was saying about the shape of the mufflers on his T-Bird. The Dunstall branded mufflers available at the above link are close if not identical to the drawing. Should look fantastic...

I will be curious to see whether I need as much enriching as the text you've provided indicates here at 6,000 ft, or if perhaps I can achieve a good mixture using the notches on the stock needles (the bike had a pair of new Amals on it when purchased but wasn't running).

I've got an AFR gauge from dialing in the DIY blow-through supercharger setup for the A-Series motor, so have welded up a little adapter pipe to insert between the head pipe and muffler to read the ratio (the heated sensor just needs to be =/>18" away from the exhaust port, which it easily would be).

That way, I should be able to get pretty close to ideal mixture under WOT and stead state cruise conditions with these mufflers and the K&N filters--which are fitted to slightly longer-than-stock threaded collars (very inexpensive from the UK even with shipping). I'll make up a little bracket to temporarily affix the gauge to the triple clamps.

 

[solomon]

found a website (that I forgot to bookmark and can't find) which showed the 'red cap' brand disassembled. One photo showed that the perforated tube had a perforated disc tack-welded in place midway along the bore.

Question: Does anyone know whether the EMGO version also has this center disc?

Frankly, I'd be inclined to knock it out, as generally with a glass-wrapped perforated tube, you do NOT want all or most of the gasses forced outward through the holes and into the packing, around the disc, and then back inward again into the central bore.

I can see the logic of what you're saying. Will blow the stuffing out much quicker if the disc blows exhaust gasses into the wadding.
If I get the ends off mine, I'll pack with this stuff below. It permanently expands on getting hot for the first time.

I'm not going to knock the disc out though. If its removal effects low-down torque, or proves noisy, there's no way of getting in there to refix it. I'm not a welder either.

Unless I decide to be prepared to ruin them, get those red ones if everything goes bottoms up. Although the red Dunstalls are always out of stock when I look.

 

[Rudie]

Some confusion apparent over "Dunstalls". The original name comes from Paul Dunstall, who was originally a successful tuner and customiser, primarily of Nortons, in the 1960's. With the British motorcycle industry's demise, Paul switched to Japanese, again primarily having a close business relationship with Suzuki. In 1980, Paul sold the rights, moving to commercial property development. The rights buyer tried to capitalise on the name but was never as successful as Paul.

Otoh, "Megaton" appears to be a relatively recent Emgo invention?

https://www.triumphtalk.com/attachments/red-cap-png.55733/

Afaik, Paul never painted the insides of his mufflers red.

View attachment 55895

They look very similar to a pair of actual "Paul" Dunstalls I have and still use (photos attached), except mine do have removeable baffles. Mine are stamped "DUNSTALL DECIBLE (sic) SILENCER".

removable baffles on those old cans?

In addition to the "Decibles", I have had:-

. A pair of "Paul" Dunstalls without removeable baffles, similar to the ones @solomon has pictured, were intended for air cooled BMW twins, did not work for me so I passed them on fairly quickly.

. A pair of Dunstall "Power" silencers (photos also attached), looked even better than the earlier longer ones but caused a deep flat spot 3,500~4,500 on a T160.

View attachment 55915

Is a sketch; as I say, I never saw actual "Paul" Dunstalls with ends like that until the "Power" mufflers - online images of "Paul" Dunstall bikes show either Gold Star-lookalikes, Norton "peashooters" or his long "Decibles".

The Dunstall branded mufflers available at the above link are close if not identical to the drawing.

Given what has happened to the "Dunstall" name since Paul sold it, be sure whatever looks like that is not just a pirate copy of that sketch with some random internals?

 

[Bloodknot]

Oh, neat, thanks for posting this. Indeed, the radius in the drawing at the outlet end seems to reflect what Bloodknot was saying about the shape of the mufflers on his T-Bird. The Dunstall branded mufflers available at the above link are close if not identical to the drawing. Should look fantastic...

I will be curious to see whether I need as much enriching as the text you've provided indicates here at 6,000 ft, or if perhaps I can achieve a good mixture using the notches on the stock needles (the bike had a pair of new Amals on it when purchased but wasn't running).

I've got an AFR gauge from dialing in the DIY blow-through supercharger setup for the A-Series motor, so have welded up a little adapter pipe to insert between the head pipe and muffler to read the ratio (the heated sensor just needs to be =/>18" away from the exhaust port, which it easily would be).

That way, I should be able to get pretty close to ideal mixture under WOT and stead state cruise conditions with these mufflers and the K&N filters--which are fitted to slightly longer-than-stock threaded collars (very inexpensive from the UK even with shipping). I'll make up a little bracket to temporarily affix the gauge to the triple clamps.

If you are thinking of replacing your header pipes I would go stainless steel. No plating issues and if they do discolour unduly you can just polish them to bring them back to as new. See photo for when I attacked the pipes on my Ducati.

On the subject of getting the mixture correct have you guys every come across Gunson Colortune, a device that lets you see the combustion flame colour.

 

[solomon]

header pipes I would go stainless steel. No plating issues and if they do discolour unduly

They go brown, not blue though. Not very attractive to my eyes.

On the subject of getting the mixture correct have you guys every come across Gunson Colortune, a device that lets you see the combustion flame colour

I've just bought an vintage little-used one. Just need to find the time now. Be interesting to see how accurate my 'by ear' tuning is.

 

[Bloodknot]

They go brown, not blue though. Not very attractive to my eyes.………………

With a little drop of this and some Scotch-brite stainless steel will quickly be back to shiny. it’s the Hydrochloric acid that does it.

 

[solomon]

With a little drop of this and some Scotch-brite stainless steel will quickly be back to shiny. it’s the Hydrochloric acid that does it.

View attachment 55945

Wow. You must have nice clean toilet at home.
I've bought some downpipes recently. Chrome, which I then sanded to try and give a satin finish. Should've got stainless steel and a pair of rubber gloves.

 

[NM Bonny]

Some confusion apparent over "Dunstalls". The original name comes from Paul Dunstall, who was originally a successful tuner and customiser, primarily of Nortons, in the 1960's. With the British motorcycle industry's demise, Paul switched to Japanese, again primarily having a close business relationship with Suzuki. In 1980, Paul sold the rights, moving to commercial property development. The rights buyer tried to capitalise on the name but was never as successful as Paul.

Otoh, "Megaton" appears to be a relatively recent Emgo invention?


Afaik, Paul never painted the insides of his mufflers red.


They look very similar to a pair of actual "Paul" Dunstalls I have and still use (photos attached), except mine do have removeable baffles. Mine are stamped "DUNSTALL DECIBLE (sic) SILENCER".


In addition to the "Decibles", I have had:-

. A pair of "Paul" Dunstalls without removeable baffles, similar to the ones @solomon has pictured, were intended for air cooled BMW twins, did not work for me so I passed them on fairly quickly.

. A pair of Dunstall "Power" silencers (photos also attached), looked even better than the earlier longer ones but caused a deep flat spot 3,500~4,500 on a T160.


Is a sketch; as I say, I never saw actual "Paul" Dunstalls with ends like that until the "Power" mufflers - online images of "Paul" Dunstall bikes show either Gold Star-lookalikes, Norton "peashooters" or his long "Decibles".


Given what has happened to the "Dunstall" name since Paul sold it, be sure whatever looks like that is not just a pirate copy of that sketch with some random internals?

Thanks for taking the time to provide this background. I didn't know but had suspected that Dunstall licensed his brand some time ago.

The UK company I linked to represents that it is selling Dunstall branded mufflers under a registered trademark. As a longtime civil litigator, I can say that, if they did not have permission to manufacture and vend them--or to vend from someone who does have a license to make them--whoever holds the trademark could sue them and recover quite a lot of money, plus get a permanent injunction to stop them. Does that mean they're legit? No, but a pretty big risk for a company that proudly discusses its business history and addresses...

As for whether the internals of the 'red cap' mufflers reflect Dunstall's original baffle design, Bloodknot said (if memory serves) that his original Dunstalls have a perforated core with a perforated disc midway along its length. Not a very sophisticated basis for a patent, and as I've said fiddling around with different core designs is fun and easy (I can weld, turn stuff on a lathe, etc.), so I'm not too worried about mucking up a perforated tube; what I don't have the ability to produce is that lovely, seamless, chromed can.

I'm not so keen on the red-painted caps, and would probably re-coat them with high-temp flat black engine paint...

As for the flat spot, the EMGO Dunstall replicas fitted by Dave of the Lemon Drizzle Gang to his '73 (?) Bonneville with a 750 kit seemed to pull very well according to him and his mate doing the video review of the bike. I see from your photos of the original Dunstalls that they actually resemble the EMGOs with the seam at the big end more than the seamless, purportedly trademarked ones I found.

I guess what all this means is I want: (1) a removable baffle, to enable rewrapping the core (by all accounts an improvement), (2) a good-quality can whose aesthetics I like, and (3) internals that mirror what original Dunstalls have. Am I missing something, or don't these mufflers possess the first and last items?

I've got time because the UK company wrote back with additional fitment questions so didn't fulfill my order--and I have yet to respond. But I'm leaning toward the seamless ones (smaller inlet I.D. part no.) rather than the EMGOs at this point...

 

[NM Bonny]

I can see the logic of what you're saying. Will blow the stuffing out much quicker if the disc blows exhaust gasses into the wadding.
If I get the ends off mine, I'll pack with this stuff below. It permanently expands on getting hot for the first time.
View attachment 55931

I'm not going to knock the disc out though. If its removal effects low-down torque, or proves noisy, there's no way of getting in there to refix it. I'm not a welder either.

Unless I decide to be prepared to ruin them, get those red ones if everything goes bottoms up. Although the red Dunstalls are always out of stock when I look.

I believe when Dave of the Lemon Drizzle Gang flashed a still shot of his '73 (?) Bonneville with a 750 kit, showing his mods, he listed Acousta-fil as the brand of repacking material he chose, too. They sound great. I'll be eager to hear your mufflers when repacked--and of course we can compare because you've provided the 'before' video.

Yes: although they are listed as out of stock on the website (both inlet sizes), Carolyne at British Bike Bits (the company I linked to) said via email "we can supply the BBBDUN silencers to order 88 (Pounds British Sterling) each plus postage and VAT": [email protected]

*Note: as I said in another post, the right part number is BBBDUN2 for the 1-3/8 to 1-1/2" inlet...

 

[NM Bonny]

If you are thinking of replacing your header pipes I would go stainless steel. No plating issues and if they do discolour unduly you can just polish them to bring them back to as new. See photo for when I attacked the pipes on my Ducati.

View attachment 55944

On the subject of getting the mixture correct have you guys every come across Gunson Colortune, a device that lets you see the combustion flame colour.

Great idea, but I don't seem to find stainless header pipes for my '71 OIF Bonneville, unfortunately.

Yes, I've heard of colortune--thank you. But the AFR gauge is more precise, I think--and I can watch the numbers under load while riding the bike.

 

[solomon]

Great idea, but I don't seem to find stainless header pipes for my '71 OIF Bonneville, unfortunately.

There's some on eBay usually. In the UK at least.q

Yes, I've heard of colortune--thank you. But the AFR gauge is more precise, I think--and I can watch the numbers under load while riding the bike

Where/how do you fit this?

 

[Rudie]

had suspected that Dunstall licensed his brand some time ago.
The UK company I linked to represents that it is selling Dunstall branded mufflers under a registered trademark.

I am almost certain that Paul sold the rights, as opposed to licensing them. He sold the motorcycle tuning and accessories business, never showed any subsequent interest in motorcycles and remains uninterested even when approached by the Norton Owners Club in recent years.

Bloodknot said (if memory serves) that his original Dunstalls have a perforated core with a perforated disc midway along its length. Not a very sophisticated basis for a patent

My "Decibles" have the same. However, mine were used when I obtained them, I could not say whether the internals were any more sophisticated when new. That said, during the 1980's, a local tuner and racer made special parts for me, he said the midway perforated disc was important.

the flat spot

It was only with those shorter "Power" silencers and on a triple. Ime, the same silencers affect triple and twin engines differently; also, unlike the Decibels, the Power silencers are not straight through, the flat spot might not be anything to do with the Power silencers' length, could be their different internals, or a combination.

 

[NM Bonny]

There's some on eBay usually. In the UK at least.q

Where/how do you fit this?

I've never used them but if memory serves, the Colortune unit screws between the spark plug and cylinder head. Gives you a visual indication of relative AFR...? Bloodknot can straighten me out if that's wrong.

 

[NM Bonny]

I am almost certain that Paul sold the rights, as opposed to licensing them. He sold the motorcycle tuning and accessories business, never showed any subsequent interest in motorcycles and remains uninterested even when approached by the Norton Owners Club in recent years.


My "Decibles" have the same. However, mine were used when I obtained them, I could not say whether the internals were any more sophisticated when new. That said, during the 1980's, a local tuner and racer made special parts for me, he said the midway perforated disc was important.


It was only with those shorter "Power" silencers and on a triple. Ime, the same silencers affect triple and twin engines differently; also, unlike the Decibels, the Power silencers are not straight through, the flat spot might not be anything to do with the Power silencers' length, could be their different internals, or a combination.

Yes - I misspoke: the article you provided suggests that Dunstall did, indeed, sell out rather than licensing. In fact, I'm thinking of doing one or the other with Creative Spridgets, and have gotten some nibbles from the big aftermarket vendors of MG/Austin Healey parts (though if selling, I wouldn't make enough to buy an English country estate!).

Okay, thanks for the additional info. For sure, the disc is important to generate the right back-pressure/wave, and who knows? I might just repack them with Acousta-fil, slip them on, and be thrilled (and periodic repacking isn't that big of a deal). But it's also neat to have the removable innards to experiment if I wish. Though in the interim, I'll certainly be busy enough refurbishing the bike over coming months per the other thread.

Re: Dunstall, I find it interesting that someone so into bikes would be so cold on them later in life. I no longer take the kind of chances I did when younger, but derive a kind of fulfillment from tinkering with and riding a vintage machine that's hard to replicate. Maybe it suggests that Dunstall was drawn more to the challenge of achieving performance and making money than to any sort of deeper affinity with the machines themselves...?

I recently wrote and briefly shopped around Hollyweird a screenplay called "A Man of Cars," that is about a fictional statute designed to force the obsolescence of internal combustion engine vehicles, which puts the protagonist at odds with the federal government--and his son, who grew up turning wrenches, gets caught in the middle. But my point is that, at least for some people, there is a fundamental difference between a vintage bike (or car) and transportation per se--and that difference is linked to a sense of self in ways that are difficult to articulate but no less profound IMHO.