[AgentX]

Saw this browsing royalenfieldzone.com: 

http://www.royalenfieldzone.com/products/accessories/large/2684.jpg

Cylinder head which takes two exhaust pipes, seems to me.  I have seen a bike or two with dual pipes here in India, now that I think about it.

Are people using this for aesthetics, or is there some actual advantage to it?  Is enough ever enough when it comes to outflow from a 350 single??  Seems if you want performance, bolting another heavy pipe to the bike might be counter-productive, no?

Please educate this ignorant one.

MD

[Arizoni]

Over the years this has been tried by  many motorcycle producers and others in an attempt to gain performance.

In one of my books they show a 1930 BSA single using a similar system.

It's just my guess but I think what little is gained by using dual ported exhausts is lost by the weight of the additional exhaust pipe and the extra cost of machining two exhaust ports.

[t120rbullet]

Kevin had a batch of those made up a number of years ago. I don't think he ever got all the bugs worked out of his and the other people that had em never said there was any improvement over a single pipe head. At least not enough to make anymore of em.
I think that the look is the only gain your going to get from it.
CJ

[Ice]

AgentX your hunches are all correct.

Two pipes in this case reduces exhaust velocity and therefore cylinder scavenging.

[Arizoni]

I agree Ice.
(hope Kevin isn't reading this  )
Most of the designers that made use of these were working on the theory that to gain power all of the back pressure during the exhaust stroke must be eliminated.
The idea of high velocity exhaust gas and tuned pipe lengths were not fully understood.

Not that it is directly related to this discussion buy my Honda 400F actually had very small steel exhaust pipes inside the outer chrome exhaust pipes to keep the velocity up to achieve not only cylinder scavenging but increased charging air inflow thru the inlet valve when both valves were open.  It worked too.  Up to 6,000 rpm it was quite docile but from 6K to 11.5K it cranked out a whole bunch of power. 

Getting back to the twin port single, another problem with having twin exhaust pipes is the extra pipe tends to block off air to the cooling fins and the air is heated a bit as it is blowing past the pipe.  That doesn't help engine cooling.

[Ice]

(hope Kevin isn't reading this  )

He is  ..well maybe not this thread but he is on the forum right now.

No worries though,
(a) he is a good guy and genuine Bullet fan of the open minded variety.
 and
(b) he wasn't expecting super duper performance with his twin port but it did have a certain kind of cool to it .

[olhogrider]

Twin pipes on a single?? What a crazy idea... unless you have seen a Honda GB500.

[barenekd]

A GB500 has dual pipes because it has a four valve head.
bare

[olhogrider]

I know. Makes it look like a twin, sort of.

[GlennF]

Its not a new idea.

The late 40's/early 50's J2 Enfield was a single with twin ports and pipes.

http://www.royalenfields.com/2010/12/twin-pipes-on-single-cylinder-royal.html

[Kevin Mahoney]

Chris is right about the twin port heads.(Twingle) I had 10 made up many years ago. I had no real expectation other than the fact that they might look cool. I put one on my own bike. I looked really cool, sounded better but only moved the performance backwards as far as I was concerned. I could not get the VM28 carb rich enough to give it a good go though.

There are nine others our there somewhere, 

[AgentX]

I doubt this is one of yours, Kevin, but thought this was a funny coincidence to see just the same:



Really was a pretty nice-looking bike.