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Paul Dunstall did something similar to this on Nortons :
Commando exhaust design ?
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baz
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Well if you can call a 2 into 1 into 2 similar to a 2 into 2 with an X shape balance tubes then yes I suppose it's similar!
Fast Eddie
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Al, looking at the thread title… and then at your post… my thoughts are: its a Laverda…
baz
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Yes but the SF was similar to a commando
A bit like an H2 and a t150 !!!!
concours
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It's rearward facing, and will deflect slightly as it gets bevelled off. No worries.
The pipe is closer to hitting....
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If you use a 2 into 1 exhaust and advance the opening point of the exhaust valve, if theyre is no restriction paat the collector, you get more torque but also more noise. The Exup on some superbikes is supposed to deliver more torque, but what it really seems to do is reduce the noise which comes from more radical valve timing.
The cross under the motor of the Laverda motor allows both header pipes to exhaust into both mufflers. So the noise problem is reduced without increasing restriction.
Paul Dunstall's exhaust had a collector which exhausted into a short piece of tail pipe which had a reverse collector and two mufflers. The Laverda is a 180 degree twin, so the pulses are not regular, as they are with a Norton engine. The SFC Laverda exhaust still seems to work well. I watched the bike in the picture trounce all the fast Z900 Kawasakis at Phillip Island , back then.
The cross under the motor of the Laverda motor allows both header pipes to exhaust into both mufflers. So the noise problem is reduced without increasing restriction.
Paul Dunstall's exhaust had a collector which exhausted into a short piece of tail pipe which had a reverse collector and two mufflers. The Laverda is a 180 degree twin, so the pulses are not regular, as they are with a Norton engine. The SFC Laverda exhaust still seems to work well. I watched the bike in the picture trounce all the fast Z900 Kawasakis at Phillip Island , back then.
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I've had a couple of Yamaha Exup valves apart on Yamahas I've owned and cleaned up the casting of the valve. It's a restrictor and it works for the intended purpose, as well as reducing low RPM noise. I've also removed the Exup and put a Yoshimura slip on in its place, and hell yes the exhaust is loud without it.
My 2 into 1 exhaust has no restriction in it past the collector or anywhere else. I does have a 20" long 1.75" diameter baffle in it that I made, and is only loud when I turn up the wick. Otherwise, it's not that bad putt putting through town.
My 2 into 1 exhaust has no restriction in it past the collector or anywhere else. I does have a 20" long 1.75" diameter baffle in it that I made, and is only loud when I turn up the wick. Otherwise, it's not that bad putt putting through town.
Matchless
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It's a 360 degree twin. The five hundred Lavs are 180 degree.
luckyed
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Yes the Laverda 750SF (and SFC) is a 360 degree crank. I currently have a ‘72 750 Roadster with an original 2-1-2 Dunstall exhaust and a ‘74 Laverda 750SF with the single fat crossover pipe underneath, rather than the X shaped crossover connection used on the Laverda SFC in the photo. Agree that keeping the center stand in a race situation is pretty questionable.
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Part of the problem is restriction. When I fitted a a 2 into 1 pipe to my Triumph motor, I immediatey lost 2000 RPM off the top. I started progressively cutting the collector back and welding on larger diameter tailpipes. I did not get decent performance until the tail pipe had the same cross-sectional area as the of that of the sum of the two header pipes' areas. The other aspect is kadency. At TDC on one stroke, both the inlet and exhaust valves are open, and mixture gets stuffed across the top of the piston and into the exhaust and then back into the cylinder, because of a reverse wave - resonance.
I think a 2 into 1 exhaust cannot work well with a 180 degree crank motor due to interference, but it would still be better than a restrictive exhaust.
With a 360 degree motor, it the tail pipe is the same length as one of the header pipes, the system might resonate with an interference effect
I actually bought some larger dianeter tube,so I could make a cable-operated EXUP for my bike. But I think two mufflers and the cross under the motor might be better The power is good, but the noise is horrible.
I think a 2 into 1 exhaust cannot work well with a 180 degree crank motor due to interference, but it would still be better than a restrictive exhaust.
With a 360 degree motor, it the tail pipe is the same length as one of the header pipes, the system might resonate with an interference effect
I actually bought some larger dianeter tube,so I could make a cable-operated EXUP for my bike. But I think two mufflers and the cross under the motor might be better The power is good, but the noise is horrible.
Paul (850 Commando.)
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180, 744cc Weslake with 2 into 1.
86 RWHP on open exhaust. With reverse cone for noise reduction and a considerable mid range gain, 83 RWHP as raced.
Attachments
SteveA
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Last edited:
baz
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I still have the two downpipes from my dunstall system
The Y at the rear rotted first so I cut that off and ran it with a single megga directly under the motor
Then the front Y section rotted through and I gave up with it
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" Paul Dunstall did something similar to this on Nortons : "
Tuned Length Headers ?
The lervoida woulda had a multitudinous lenght header effect , wonder if pulses self select the most advantageous pulse channel ?
While we're on the subjects of zorsts , this I thinks the ' far out and groovey ' system , for a Commando . Tho these early headers
kink straighter outta da head ( pipe to flange tube join ) AND they aint gunna fit yr syock footrest angers .
THE PRIMARY ' THING ' Is The Pipes TUCKED UP inside the case join flanges . So Yr notta gunna getta Side stand , in a hurry , Either .
lug outside the lower frame toobs gotta go .
tho early underside cross tube brace mount type fitting might be fittable ? .
lcrken
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I don't recall ever seeing any X crossover Norton pipes by Dunstall. Pretty much only the ones in the pics below:
First, the Commando system most of us are familiar with.
Prior to that, he produced this balanced pipe system for Commandos.
He also produced swept back pipes with a balance pipe as well as a siamese pipe for earlier Norton twins. Not sure if they were available for Commandos.
That's it for the systems I know of that he sold to the public. He also made race systems for his race bikes, but the only ones I've seen are simple pipes with megaphones, no crossovers or 2-into-1 joins.
Ken
First, the Commando system most of us are familiar with.
Prior to that, he produced this balanced pipe system for Commandos.
He also produced swept back pipes with a balance pipe as well as a siamese pipe for earlier Norton twins. Not sure if they were available for Commandos.
That's it for the systems I know of that he sold to the public. He also made race systems for his race bikes, but the only ones I've seen are simple pipes with megaphones, no crossovers or 2-into-1 joins.
Ken
