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650 pipe diameter... #620510
10/04/15 7:13 pm
10/04/15 7:13 pm
Joined: May 2013
Posts: 743
Overland Missouri
O
old mule Offline OP
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old mule  Offline OP
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Joined: May 2013
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Overland Missouri
I'd like to read a little about exhaust pipe diameter. On my 650 sidecar outfit, I have always used an old police "Saint" siamesed system, 1 3/8 diameter. The silencer is from a racing Trident, source unknown. It's a little louder than I'd like, but not obnoxious.
In my day it was said that bigger pipes were good for top end HP, and the smaller diameter ones for "torque and mid-range".
That was all folk wisdom from pre-internet days.
So....for a 650 unit Triumph, on standard gearing, that is driven between 55 and 70 mph most of the time, one carb motor, what would be the exhaust system best for my application? Silencer(s)?
I like having the single silencer, as there is one less thing to rust away, crack, or fall off...
Any advice, folk or scientific, welcome.

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Re: 650 pipe diameter... [Re: old mule] #620523
10/04/15 10:20 pm
10/04/15 10:20 pm
Joined: Jun 2007
Posts: 5,910
Maui Hawaii
HawaiianTiger Offline
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HawaiianTiger  Offline
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Posts: 5,910
Maui Hawaii
Kind of a gray area here. Lots of folks swear that their bikes are faster if they're louder, but really? Maybe they are at top end but who rides like that? I'm not 18 anymore. I like quiet pipes or at least just audible at highway speeds. Any more is obnoxious to me not to mention anyone else.

I had a siamese system on a 650 once, but I didn't really like it. I think it robbed power and the sound wasn't all that pleasant. I changed to a twin system and it woke my bike right up.

You can choose between a crossover type twin system or separate pipes, too. Some say the crossovers spread out the power, but I'm undecided about that. They are marginally quieter though.

The standard 1&1/2 inch pipes are my choice for best powerband. I'm not well versed in the science of exhaust scavenging, but there something to be said for the smaller pipes and it makes sense to me. Triumph began using them in the late 50's and stuck with them so they must have something going for them.

One thing I'm certain of is that TT pipes aren't very good on the street. First off, they're ridiculously loud. Second your low end and midrange will likely be negatively affected. Third, your carb may need adjusting to suit and predicting what that will be is near impossible.
Lastly, if you don't know how to tune your carbs to suit the pipes, you could seize your engine or hole a piston.

I've been using single 1&1/2" down pipes and Norton style peashooters on bikes lately and it's a winner. Great sound, broad spread of power and no messing with carbs required. I like the looks, too.

For a stock motor, I've never seen an exhaust better for ordinary riding that the stock twin setup. For a high output motor, a freer flowing exhaust may be better.

Cheers,
Bill


Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Flying Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
Re: 650 pipe diameter... [Re: HawaiianTiger] #620683
10/05/15 8:34 pm
10/05/15 8:34 pm
Joined: May 2013
Posts: 743
Overland Missouri
O
old mule Offline OP
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old mule  Offline OP
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Overland Missouri
Thanks- I like the two-into- one a lot, wish someone made a left side 1 1/2 inch low two-into-one, I'd like to try the bigger diameter and my sidecar passenger would be happier if the sound wasn't twelve inches below her ear- that's the main reason I like quiet silencers.
Kind of hard to find info on pipe diameters, gas velocity is supposed to be better with the smaller pipes, but I can't seem to find much written for Triumphs on the subject.

Re: 650 pipe diameter... [Re: old mule] #620705
10/05/15 10:42 pm
10/05/15 10:42 pm
Joined: Jun 2007
Posts: 5,910
Maui Hawaii
HawaiianTiger Offline
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HawaiianTiger  Offline
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Posts: 5,910
Maui Hawaii
Hardly useless info. Thanks. I got great performance from my Jardine two into one system on a Routt kitted 67 Bonnie years ago. Fantastic sound and great big lump of power in the midrange. It was a 1&3/4 inch downpipe system with a tuned muffler. They put bikes on dynos and tuned the pipes for the best power. Not available anymore, sadly. So, there may be a market for a tuned two into one system for some folks, especially sidecar drivers.

Cheers,
Bill


Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Flying Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
Re: 650 pipe diameter... [Re: old mule] #620754
10/06/15 8:55 am
10/06/15 8:55 am
Joined: Jul 2012
Posts: 1,633
UK Berks
A
AngloBike Offline
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UK Berks
what Saint had a 2 into 1?

Re: 650 pipe diameter... [Re: AngloBike] #620779
10/06/15 1:00 pm
10/06/15 1:00 pm
Joined: May 2013
Posts: 743
Overland Missouri
O
old mule Offline OP
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old mule  Offline OP
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Joined: May 2013
Posts: 743
Overland Missouri
Mine has a 1963-4 part number, I had assumed all police bikes had them.

Re: 650 pipe diameter... [Re: HawaiianTiger] #620780
10/06/15 1:01 pm
10/06/15 1:01 pm
Joined: May 2013
Posts: 743
Overland Missouri
O
old mule Offline OP
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old mule  Offline OP
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Overland Missouri
Maybe when the time comes I will make one, 1 3/4 inch chopper pipes are almost free at swap meets, I could cut and shut a system I suppose.

Re: 650 pipe diameter... [Re: old mule] #620869
10/07/15 8:25 am
10/07/15 8:25 am
Joined: Jan 2011
Posts: 172
Pt Augusta, Australia
M
Mossy Offline
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Mossy  Offline
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Pt Augusta, Australia
Personally if your only cruising from 55-70 mph it probably doesn't matter what the exhaust diameter is.
I can tell you that my 54 Thunderbird produces 2 hp more at 7,000rpm on 1 3/4" pipes than it does with 1 1/2" pipes.
Cheers Mossy


1960 TR6B
1954 based Thunderbird Salt Lake Racer
1979 T140E
1951 6T Thunderbird Project
1981 T140E
1948 Speed Twin project
1976 Bonneville/Tiger Trail replica
2015 Bonneville T100
1949 Excelsior 197 Roadmaster project
1950 Excelsior 250 Talisman project
Re: 650 pipe diameter... [Re: Mossy] #620923
10/07/15 2:57 pm
10/07/15 2:57 pm
Joined: Jun 2007
Posts: 5,910
Maui Hawaii
HawaiianTiger Offline
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HawaiianTiger  Offline
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Posts: 5,910
Maui Hawaii
Sounds about right, but I suspect the motor makes more usable power in the lower rev ranges with the smaller pipes. Did you find this to be true?

I've never been happy with the power of my 'Bird with the 1 & 3/4 inch pipes...


Cheers,
Bill


Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Flying Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
Re: 650 pipe diameter... [Re: old mule] #620937
10/07/15 4:26 pm
10/07/15 4:26 pm
Joined: Jan 2011
Posts: 172
Pt Augusta, Australia
M
Mossy Offline
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Pt Augusta, Australia
Bill
At 4,500 rpm it was producing around 5 hp more with the 1 3/4 pipes.
Mind you the 1 1/2' pipes also had meggas.
You will probably find the different exhausts suit different cams as well.
Cheers Mossy


1960 TR6B
1954 based Thunderbird Salt Lake Racer
1979 T140E
1951 6T Thunderbird Project
1981 T140E
1948 Speed Twin project
1976 Bonneville/Tiger Trail replica
2015 Bonneville T100
1949 Excelsior 197 Roadmaster project
1950 Excelsior 250 Talisman project
Re: 650 pipe diameter... [Re: Mossy] #620948
10/07/15 5:35 pm
10/07/15 5:35 pm
Joined: Aug 2001
Posts: 7,455
scotland
triton thrasher Offline
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triton thrasher  Offline
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Posts: 7,455
scotland
Originally Posted By Mossy

Mind you the 1 1/2' pipes also had meggas.


So do you have no comparison between exhaust systems where the only difference is diameter?


Amateur Loctite enthusiast.
Re: 650 pipe diameter... [Re: triton thrasher] #620967
10/07/15 8:23 pm
10/07/15 8:23 pm
Joined: Oct 2012
Posts: 3,730
Running from demons in WNY
Hillbilly bike Online content
BritBike Forum member
Hillbilly bike  Online Content
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Joined: Oct 2012
Posts: 3,730
Running from demons in WNY
Here's my 650 Triumph race bike dyno runs from last year.These tests show a modified engine can producer more midrange power than a stock engine, not what people normally think abour modified engines.....This is rear wheel power...The first two columns are the so called "Dyno Jet" power.Third and forth columns are net power as seen on an eddy current Superflow dyno .Dyno Jet is the most common type and Superflow power readings are considered to be very conservative. Disregard the air fuel readings...The second column is the torque..Notice the peak torque @5100 rpm ,which is more torque at a lower rpm than a stock 650 Bonneville. The torque remains above 40 Ft lbs until slightly over 7000 rpm.. It's torque that makes things go fast..
Keep in mind this engine has 10.5 compression , Sifton 390 cams that are a step above the #3134 stock cams but not radical . And big 34 MM Mikuni flat slide carbs with 1-1/2 individual 38 inch straight pipes.
There's notes on the test printout about velocity stacks ,filters and exhaust changes and restrictions to test the theories that open pipes reduce power..The engine made the best spread of power as mentioned above...






Last edited by Hillbilly bike; 10/08/15 7:32 am.

I ride junk
Re: 650 pipe diameter... [Re: Hillbilly bike] #621076
10/08/15 4:55 pm
10/08/15 4:55 pm
Joined: Oct 2012
Posts: 3,730
Running from demons in WNY
Hillbilly bike Online content
BritBike Forum member
Hillbilly bike  Online Content
BritBike Forum member
Joined: Oct 2012
Posts: 3,730
Running from demons in WNY
And like Bill said some bikes don't like open pipes. I'm doing typical maintenance on this bobber I built for a guy about 5 years ago. He said the engine midrange throttle response is soft. Stock single carb 650..He put on very long 1-3/4 inch open pipes causing some reversion...
Something simple like these home made "Lollypops" used by Harley riders can often help reduce reversion if the pipes must stay as they are...
They do restrict the top end a bit but for a bike like this it's no big deal.
Yes,that's my balance weight on the wheel... grin



I ride junk

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