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Did I read on the forum that the 650 motor actually can deliver more power with the slightly smaller 500 pies? Thr reason I ask is that I had my head done a Memphis Motor Werks, it had smaller stubs installed. I thought at the time it was a mistake. So I put in a regular set. The bike runs awesome after the work done on the head, but I keep wondering. I should just call him, but he has been hard to reach for medical reasons.

If any tuners out there could let me know if there is something to this.

Thanks in advance,

Ken

Last edited by Vintmoto; 10/09/20 3:00 am.

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The firebird has smaller pipes than the other A65’s they have a lot of torque, lower down and rev, on paper they produce more HP at higher revs than a lightning.


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Most 650's that I've seen already have 1 3/8" pipes. The head spigots are 1 3/4" and pipes are necked down or in the case of TT pipes that stay at 1 3/4.
I have a set of 500 pipes that are 1 1/2". Thats a bit of a head scratcher for me.

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This is confirmed in Mr Pike memoirs - Ariel copy of A10 had worse acceleration / speed and less horsepower because of bigger diameter exhaust pipes. Smaller diameter pipes give better speed of exhaust gases. This is I think why Japanese manufacturers developed double exhaust pipes, they optically look bigger and don't discolor the chrome on them.

Last edited by Adam M.; 10/02/20 8:52 pm.
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Beginning in 1957 Triumph offered "high performance" exhaust pipes as an accessory for the T110 model.
They were the "necked down" smaller pipes we are familiar with.

The reason for calling them "high performance" being the venturi effect which drew the exhaust out faster.
These pipes became STANDARD on 1958 and later models.

If I'm mistaken on this, I hope John Healy will correct me.

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What I have heard and read is that the 1.5" pipes are better for WOT racing.


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Thats not what Paul Dunstall found


71 Devimead, John Hill, John Holmes A65 750
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It's all too technical for me, i thought it was a good idea to have smaller pipes
if they had to bend sharply, large radius bends can use bigger pipe diameter.
Best left to testing and setting on a dyno as an individual case.

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I once read a book on exhaust design, one of those from the basement of the university library where they keep all the good secrets. Don't remember much about pipe diameter, but the length is critical for tuning to the correct RPM range.
My only experience with this is with my A65, which has adapters for Triumph pipes. The first set of pipes I bought for it were 1 3/4" straight through to the mufflers, which were 20" long baffled megaphones. That bike now has pretty standard Triumph pipes, 1 1/2" ID. Maybe faster, maybe not, but it has a better, wider power band.
Depends on what you want from the bike. Triumph Speed Tuning recommends, "The best racing system for the 650cc twin is two separate pipes, each 37" long and of 1 3/4" internal diameter." Probably great if you're running around at 6-7000rpm all day. Not so much for the street.
Then you get into carb jetting. My Trident has a 3:1 system on it. The head pipes are larger diameter than stock, and I'm pretty sure the muffler is less restrictive. It runs best with 170 main jets, as opposed to 150, but the needle must be in the lowest position to avoid midrange reversion.


"Gosh, it's not a 1/4 20, must be metric."

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Originally Posted by gavin eisler
Thats not what Paul Dunstall found

Not quite sure at where your comment is going Gavin, but this is my observation with his silencers.
I have 3 different original Dunstall silencers, two sets are the decibel type with the 7 tubes formed to make a circle. One set is different from the other in that this end piece is smaller on one than it is on the other one.

The other silencer I have (and just fitted) is a Dunstall power silencer, this is very different. It’s a straight through solid 35mm (ish) pipe, but there’s access for gas to pass outside this pass and through some form of baffle (from what I can tell, I haven’t taken it apart) at the exit end the solid pipe has a flat section with rolled edges, the outer of that will let gas pass.

[Linked Image]

[Linked Image]

An observation on the pipes is when I made them I added a fillet to the bottom of the pipe where it enters the head. It’s made jetting very difficult, I removed this filllet the other week, with some detriment. A defined increase in exhaust note being one, the other was a drop in midrange torque, which was pretty annoying. You get used to leaving the bike in a set gear and it’ll pull through all the twisties, now I’m back up and down the box between second and third... maybe I’m just idle.


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I wasnt referring to the Dunstall Decibel loudencers. In the 60s the Dunstall Domiracer was a force to be recconned with.
The pipe headers exited at the stock diameter, were united by a balance pipe, after the balance pipe the diameter stepped down until the silencer where they stepped back up. I have a set somewhere, next time I am in the attic I will take a few pics, unfortunately they are swept back and wont fit my bike.

I just googled Dunstall Domiracer, couldnt find any images of the stepped down pipes! however i clearly recall a Motorcycle Mechanics article in the 60s explaining their merits, most online images show unbalanced unstepped systems on more recent rennovations.

Last edited by gavin eisler; 10/03/20 10:22 am.

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Originally Posted by gavin eisler
I wasnt referring to the Dunstall Decibel loudencers. In the 60s the Dunstall Domiracer was a force to be recconned with.
The pipe headers exited at the stock diameter, were united by a balance pipe, after the balance pipe the diameter stepped down until the silencer where they stepped back up. I have a set somewhere, next time I am in the attic I will take a few pics, unfortunately they are swept back and wont fit my bike.

I just googled Dunstall Domiracer, couldnt find any images of the stepped down pipes! however i clearly recall a Motorcycle Mechanics article in the 60s explaining their merits, most online images show unbalanced unstepped systems on more recent rennovations.

That would be really good if you can Gavin,

There’s a lot of aftermarket stuff, often branded as Dunstall but without the same features that the original parts had.


Now let’s all have a beer beerchug

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...why Triumph changed for the long silencers? I have the emgo copy I think, seems that PO did something or removed something inside due to they cut them near the end then welded back (no more chromed in that part)
I checked inside with a LED light but I cannot decipher all the stuff that comes inside.
Some mentioned that without them the bike could run faster but I have Mikuni s in this bike and have been very complicated to get its running good so no time to remove silencers and do all the jetting again.

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Depends which silencers your on about reverb? I believe the original megas we’re made to try and meet noise regulations... or maybe that was the later c1975 megas??


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[Linked Image from luxuryautomotosale.com]
[Linked Image from luxuryautomotosale.com]
[Linked Image from s14.postimg.cc]

Last edited by quinten; 10/04/20 8:41 am.
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Circle no. 40 on reader service page grin Hadn't thought of those in years, I used to send them in all the time! Times have changed.
...so has the price of pipes

Last edited by slofut; 10/04/20 2:01 pm.

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Hi Allan;
I am referring to the 79 silencers that are the long ones.

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I'm sure that the 'cigar' silencers of '74, and the ones on T160 and Mk3 Commando, were there for noise abatement. The cigars certainly have no other redeeming qualities.
I put peashooters on my '74 T150 with good results.
Many aftermarket silencers made to look like the '71-2 are sold as "Dunstall."


"Gosh, it's not a 1/4 20, must be metric."

72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"


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