I'm still looking through my options to change my exhausts, how does the engine respond to each exhaust? There was a post somewhere but I can't seem to find it.

Hiya Simon,
I was wondering same thing very recently having read and read exhausts on this forum I went for the MTC stainless Oval and can personally recommend them. Cracking noise with baffle in but the last couple of rides I have had the baffles out even better in my opinion.

Also rang insurance to let them know informed them they were cosmetic and answer that will be no cost I will stick a note on your file and sort next time you re-new.

Cant comment on the 2 - 1 others will probably have information on them but for me mine look good, sound good, value for money and lifetime guarantee.

that is M.H.O. for what its worth,
Steve

Someone must explain the technicalities involved between the two types.
I was told the duel pipes have less back pressure but the Barrett single pipe on my bike in Aus has a bigger outlet than the twin Scorpions on my bike in SA.
Both make enough noise with baffles in. The twin pipes look more balanced and pretty from the rear end. The single leaves space on the other side for tool tube. Performance wise I would venture to say there is not much if any difference. It depends more on air filters and F/A ratio settings, etc, IMHO

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2014 XT660Z - Barrett pipe, DNA stage1.5, Barkbuster hand guards and handlebars, Pivot pegs, Teknik suspension, Guard-it engine protector combo, B&B rear rack, Trax topbox.

If i'm correct, you can see in some tuning topics that Kev's conclusion is that 2-2 has the most power

But i doubt you'll notice the difference. You'll gain anyway by letting the engine breathe more freely...

Fully agree with the above. Should you want to move heavily into power tuning then definitely you have to go for twin. You will be able to squeeze few HP out of this configuration.

However the 2in1 has few advantages. It saves more weight, gives more ground clearance. If you are taking the bike into heavier off reading this will be a great advantage. A disadvantage though is the heat in those hot days as the pipes are routed on the side of the engine. You will feel hot air blowing. The twin option does not have the heat problem.

To sum up will be your personal preference. I personally like the looks of the 2 in1 for the R and am ready to live with the hot air

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that is how i feel about my XTR
Mods so far:
Hyperpro front springs; Hyperpro rear shock spring; modified air box; LED tail light; LED indicators + new relay; YZ pegs; Lucas aluminum bar; brisk spark plug; snorkel removed; DNA stage 1; second hand DynoJet O2 mod; crash bars; front and rear steel braided brake lines; soft EBC brake pads; mitas 07 tyres, 2in1 Metal Mule exhaust, Blocked AIS, tall OEM screen, OTR bash plate

In theory a 2-2 system will produce better power at the top end of the rev range due to it's larger effective overall tube diameter, whilst a 2-1 will favour power at the lower end or the rev range as the effective diameter is smaller.

It is a good deal more complicated than this though. It is all to do with exhaust gas velocity (EGV) and exhaust gas flow (EGF), or rather the balance between the two. Essentially a narrow diameter pipe (2-1) will increase EGV and skew the torque curve towards the lower end of the rev range, a wider pipe will skew things towards the upper end.

Ideally you want an exhaust system where gases exit the combustion chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you also want make sure the pipe is wide enough so that there is as little backpressure as possible while maintaining good exhaust gas velocity. The trick is to have a pipe that that is as narrow as possible while having as close to zero backpressure as possible at the RPM range you want your power band to be located at.

A perfectly tuned exhaust system will have high velocity, and will create a negative pressure area in the exhaust port exactly as the exhaust valve is opening. This makes the high exhaust velocity pull (scavenge) the gases out of the cylinder. Otherwise (if the exhaust is too wide and free-flowing) the piston needs to PUSH the exhaust out, as well as get the static/slow moving gases in the pipes moving as well which creates high pumping losses and robs power.

Now on single cylinder engines running at relatively low rpm, exhaust design isn't all that crucial and the differences minimal. Much less so than on multi-cylinder bikes where the power pulses from different cylinders can be tuned to help scavenge the combustion chambers during valve overlap (or hinder scavenging if the exhaust is designed badly). Now on a parallel twin for example, the differences between a 2-2 and 2-1 system will be significant, but on a single it's all a bit academic. A single will run perfectly happily with a single exhaust port and header (or a suitable diameter) - take the KTM 690, that makes plenty of power with a 1-1 system.

You may well find more power with a 2-2 system, but that is just mathematical power more often than not. Due to the fact the peak torque, although in might be the same as with a 2-1, it will move upwards in the rev range and because of the way horsepower is calculated from torque (torque x rpm/5252), means that on paper the engine produces more power. Remember a dyno can only read torque, horsepower isn't measureable in itself. Basically 1lb/ft of torque is worth more in terms of calculated horsepower at 7000rpm than it is at 6000rpm. However, the slower EGV in a 2-2 may well make the engine feel less tractable and torquey than with a 2-1.

Whatever you choose, the differences will be minimal and as previously mentioned, things like styling, weight saving and ground clearance are probably more important factors to consider. Just go for the one you like the best!

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Having read the theory I agree with it,the problem being I found the reality to be totally different.

I bought my X already with Akra's on I also use Akrapovic on the other bikes and IMO their the best in the world but one is always looking for something else,it took me nearly a year to get a decent 2 into 1 off ebay a Metalmule, I'd have liked an OTR but wasn't prepared to buy new because I knew it was a risk going to a different configuration.

Fitted the Metalmule and it looked great and the bike looked 100lbs lighter,from the moment I started the bike up I realised it was a whole new ball game,went and test rode the bike and it was like riding a totally different animal,it had gone from a bike that pulls second gear from the lights without a second of hesitation to a real old fashioned thumper.

Without putting too finer point on it I was horrified,I'm lucky in the fact I don't pay for fuel maps or dyno time and maybe with some fettling it may have come better but it wasn't where I wanted to go,within an hour the Akra's were back on and I blasted around the block and I was relieved.

Anyone going from a stocker will be pleased with either,if you own a 660r and green lane or offroad or going around the world then I'd look at a 2 into 1,if you looking for a more spritely motor with more get up and go then you'll be looking at a 2 into 2 and the bells and whistles to make them work.

At the risk of getting into the theory side have a look at MX1,thats the 500 motocross championship for those that don't watch they run single pipe systems because they need bottom end,now look at world Supermoto you will see the odd single exhaust bike but the majority want HP and revs and hence why they all run twin pipe systems.

It looks like the 2-1 system suits my needs better performance wise. Also looking at my current system I can only guess it was made out of cheese. So after running the maths junking the OEM currently fitted and putting a metsl mule system in might be a better cheaper option. Cheers for all the technical info guys.

The problem with 2-1 systems (like the Metal Mule) on the R/X is less to do with the fact they are 2-1, but more because they ALL have unequal length headers. Primary pipe or header length has a similar effect on exhaust gas velocity and flow as diameter does. The longer the header the faster the gases flow. The exhaust valve on the short header will scavenge better at high rpm as it has slower EGV than the longer one which will have increased EGV and therefore work better at low rpm. This discrepancy between the two primary pipes, and the fact that they are fighting against each other, will not help the engine to work at it's optimum efficiency.

2-1 pipes appear to work well on the Tenere and produce good torque and hp across the rev range because they use the stock equal length headers and collector.

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Hello, After going from AKRO TWIN PIPES oops, to metal mule single. The low end power is much better. It gets hot tho, not too much.

What i would like to know is, SURGING !! i know its probably been covered a million times, the bike now seems much worse around town. Lovely once its moving.
Would the Kev mod and O2 controller fix this so its smooooooth ?

cheers

dave