2 into 1 exhaust

[Bitza]

OK all, so what is the thinking on 2 into 1 exhaust systems, specifically on 1100 2v engines? They seemed to be favoured on the 750cc F1 type era bikes. Potential weight saving if nothing else.
To quote the Bonzos "to save some more weight off came my left leg.... watch out there's a monster coming. (sorry about that, but I've never found an apt excuse to quote that before). Anyway please discuss the 2 into 1 bit.

[900Rebuilder]

No idea on performance gains other than weight but personally prefer the looks and sound of two into two.

[Nasher]

I believe certain model years of the 600SS came with a 2 into 1, but it didn't last long.

[Dukedesmo]

Don't know if there is any performance benefit or otherwise? but obviously a weight saving (so a performance benefit).

Utopia has a single exhaust on his M750, I think for lightness and a 'less is more' philosophy.

Otherwise I'm pretty sure all (old) Monsters had 2 exhausts probably for aesthetic reasons? but, as above I think some of the smaller engined SS models came with a single can.

[crawsue]

IMHO the sound is more “booming” from twin cans, my 696 with Leo Vincis made a more pleasing sound than my Evo with the Remus…..but there must be a fair weight saving ….

[utopia]

Originally Posted by Dukedesmo

Utopia has a single exhaust on his M750, I think for lightness and a 'less is more' philosophy.

Exactly so.

I can't imagine there's a huge difference in performance between the two styles.
After all, on a monster each cylinder exhausts through both silencers so even though its a twin-can system it must function much like a 2 into 1 but with two silencers on the outlet from the collector.
Add to that the uneven firing of the 90 deg motor which must make the timing of the reflected exhaust pulses almost impossible to optimise if they're "mixed".
Whereas in a "conventional" twin-can system each cylinder has its own individual pipe and silencer, making it much simpler to tune the reflected pulses.
The early racing MVs, Hondas, Benellis etc. all had individual pipes for each cylinder, presumably for the above reason, but then again they were straight through pipes and so there was considerably less weight penalty from a four pipe system than there would be on a road bike running silencers.

On a road bike there will be much more weight to be shed by losing one silencer (with its heavy innards) and in my opinion this is well worth taking advantage of.

I like the practical simplicity of a single can system as it makes access for cleaning and maintenance a little easier.
I also find mechanical simplicity appealing in its own right in a purist kind of way.
And personally speaking, I find the asymmetry of a single can system visually appealing, particularly in combination with the matching asymmetry of the fore and aft, 90 deg spaced cylinders of the Ducati motor.

On the downside, where one can is doing all of the silencing for the entire system (remember that each cylinder exhausts through both silencers simultaneously in the std system), I imagine its harder to keep the noise level down. That has been my experience anyway, albeit fairly limited.

To sum up, performance gains are of lesser importance to my mind but the loss of weight and both the mechanical and the visual simplicity make the single can system my personal firm favourite.

For those that are wondering ... my own M750 runs a big bore, thin-wall, 2-1 high-level Sil Moto system originally intended for an M900 but cut down to suit the dims of the 750 engine.
It weighs bugger-all and it shows off the rear end nicely (without resort to the abomination of a single sided swingarm).
Coupled with its short..ish, straight through carbon can and a homemade db killer, I struggle to keep it quiet.

[Mr Gazza]

There will certainly be a weight saving and little drag too.
I reckon you should be able to coax a hp out of it with a bit of thought, or possibly make it worse without?

With what little I know, it's all down to the exhaust pulses and how they join together in a common tube.
On an L twin the pulses are uneven, two close together and then a big gap on each cycle.
I reckon that if you were to make the trailing pulse arrive at the junction a bit later by using a longer pipe for that cylinder, it might even things up and make the flow in the pipes better.
If you got it wrong and gave the first pulse the longer pipe it would bring them closer together with adverse affects.
No idea which fires first or second? Hopefully its the vertical that's first as it would be difficult to lengthen that one, whereas the front pipe has already got a head start.
Maybe the standard system already addresses the above as they have different length headers for each pot as far as the collector.

Note that on the 1200 they Siamese, and they have obviously gone to convoluted lengths (See what I did there?) to get the rear pipe longer.

Conversely I think it's the Cagiva Elefant that has nearly no rear pipe at all!

There must be something about this in Phil Irvins "Tuning for speed" if you can find a copy

[Dukedesmo]

Note that pretty much all the newer Ducati Superbikes and race bikes use a single silencer.

Probably for packaging and cost reasons but they wouldn't be doing it if they couldn't get at least the same performance as with a pair.

[Nasher]

By coincidence today this popped up:
https://www.ebay.co.uk/itm/196241312...temCondition=4

Nothing to do with me.

[Mr Gazza]

Is it called Staintune because it's stained black?

The pipes on that look about the same length by eye, so it should retain the lumpy beat of an L twin. I notice that someone has taken some trouble to try and get rid of some manifold heat too, with the serrated retainers, unlike that supposedly Ti item posted recently.

The seller says he thinks it will fit Monsters too, but alas I'm sure he's wrong as the swinging arms differ where they are cross braced and the rear pipe clashes if you try and swap Monster and SS systems. Good design though.

If you're thinking of having a go yourself Mike (I assume you are?) You could do worse than starting with a Monster system and some bends from here > https://www.everyexhaustpart.com/car...nds-and-elbows

[Kato]

In a Nutshell
Advantages obtained or not with any configuration vary greatly according to the shape, length, and curves of the pipes.
However
2-into-1
Generally, more common on smaller, engine bikes where the advantage is power increase and the power delivery, especially at low RPMs.
2-into-1 exhausts often offer a better-balanced airflow which can result in more torque and a smoother idle.
2-into-2
Are more common on Big Sports bikes, and perform best at high RPMs, making them best for top-end performance, but leaving a little emptiness at lower RPMs.

[RichardDDuke]

Am toying with the idea of fitting a 2:1 exhaust on my SS Monster hybrid, using the down pipes from a Scrambler and fabricating a short link tube to a single "silencer".

Not really after top end performance, so want to try it out to see how it turns out.

Wish me luck ...

[Kato]

If not after max performance and don't mind dropping an HP or two then go with what you think looks good, worst case will mean needing to sort out fueling

Biggest mistake people make is thinking bigger the bore the better

[RichardDDuke]

Pipes I'm hoping to use are off a 800 Scrambler, so pipe diameter / bore shouldn't be too dissimilar to the original 900ss ones ...

[Bitza]

Thanks for the feedback, all pretty interesting. Had a thought myself, one issue seems likely to be the size of silencer required to achieve comparable dB levels to a 2 - 2system. My thinking is that the gases have to pass through twice as fast i.e, giving half the time to do the silencing bit. If you need double the size of silencer then maybe the weight saving potential ain't so great. Another issue might be the restriction created, maybe larger internal dia? but then reducing the gas to baffle contact, meaning more length again?