Mod'ing stock exhaust - 2-1 --> 2-2

Originally Posted by ThEGr33k

Why make it 2-2? You wont really benefit in any way I can see and weight will be increased.

Sound; 2 slightly differently pitched cans sounds very impressive. Some people like the looks too.

[squirrel_hunter]

But if I were to want to pay attention to the flow and performance of the system if I were to make one of my own design what would my considerations be, or more importantly how would one shape the pipes?

My understanding would be both pipes need to be the same length, which is why the rear outlet bends before joining the front pipe on the standard system. Renegade for example leaves this join in and then splits from there, is this the best approach or should both pipes be separate?

Originally Posted by Ceri JC

Sound; 2 slightly differently pitched cans sounds very impressive. Some people like the looks too.

Cant disagree as my bike has two... Other than noise I dont think there is a reason, as YC said really.

Better off spending your money else where... unless you just want to make an exhaust to show you can?

Make it with only really short sections welded like you find on the bling bikes

[yorkie_chris]

Originally Posted by squirrel_hunter

But if I were to want to pay attention to the flow and performance of the system if I were to make one of my own design what would my considerations be, or more importantly how would one shape the pipes?

My understanding would be both pipes need to be the same length, which is why the rear outlet bends before joining the front pipe on the standard system. Renegade for example leaves this join in and then splits from there, is this the best approach or should both pipes be separate?

But then the 2 link pipes are of differing lengths too...

System needs to be big bore, smooth curves, equal length headers and polished internally. Shaping tubes is either done with a pipe bending machine or by welding together cut cones, premade bends etc. Collector design is the hard bit, a proper system will be modelled in CFD to optimise flow, but that's beyond most folks shed capabilities lol.

p.s "backpressure" is odd one, adds midrange on a motor with hot cams, but saps top end power. Hence use of EXUP valves on motors with hot cams...

Originally Posted by squirrel_hunter

But if I were to want to pay attention to the flow and performance of the system if I were to make one of my own design what would my considerations be, or more importantly how would one shape the pipes?

My understanding would be both pipes need to be the same length, which is why the rear outlet bends before joining the front pipe on the standard system. Renegade for example leaves this join in and then splits from there, is this the best approach or should both pipes be separate?

As I mentioned you could make the pipes out of short sections (couple of inches) and weld them togther. Similar to on the exhaust here http://www.motorcyclenews.com/upload...IKI%20%203.jpg

Positioning try maybe Motogp style? with the exhaust staggered or in different places. Would be pretty cool

Yes the two exhausts do need to be linked but dont have to go as extreme as 2-1-2... all they need to do is alow a little pressure through which helps back pressure and engine performance (apparently). Unfortunatly I dont know the exact physics behind this though Sorry.

[yorkie_chris]

Yup stacked cone type ... 2 stroke race engine builders have been doing that since the stone age. You ever tried welding thinwalled pipe though? Controlling distortion is an art.

For best power I'm fairly sure that a pair of very big bore pipes going straight out by the straightest, shortest route would give best top end power. But I reckon that would also totally b0llocks the midrange.

P.s with system flowing so much fluid it'd have to be a fairly large join to affect the pressure.

Hey lads - thanks for all the replies - as said above the only reason I'm doing it is for looks & hopfully sound... I was thinking of buying 2 aftermarket cans and doing it that way also (2 fuel or CCC cans would do the job)

Was thinking of making it hi level also...

Working with metal is no problem, thinwalled welding is fine also. I didn't think about the weight -

[squirrel_hunter]

Ok I didn’t quite phase part of that last question in the best way; I meant how would one shape the pipes in relation to their look or design, not how to make the pipe work itself.

Taking the assumption that the straightest route would give you the best top end but leave you nothing else, and accepting the fact that you would want some mid range etc, and placing CFD out of scope. Have we concluded that the pipes should be joined or not? And going back to the original point how would you improve the flow with a twin system or what is so bad about the current market offerings?

[northwind]

I would say personally, don't get too hung up on it. There's a very simple test you can do to put the theory of equal length headers into practice, with the SV- there's a split in the frotn header so with a spanner and a bit of persuasion you can alter the length of the front one by about an inch, then see what changes. Absolutely nothing, as far as I can tell But ymmv.

I remember an interview with Igor Akrapovic where he said that before they had their flow modelling software they used to work not on equal lengths, but equal volumes, so the testing system was a big jug of water But then he also said of the 06 R6 that all of the numbers for their exhaust for it look wrong on paper, but that it's the only one that works properly.

Fluid and gas modelling is still not as exact a science as it could be, especially when you add in major heat changes etc. Lots of unpredictable results...

Originally Posted by jameshayes

is it possible to buy a 2nd hand stock exhaust and modify my own twin system?

Yes, this is exactly what Renegade did to not much success.

Originally Posted by Ceri JC

I think he was suggesting that most of the existing 2 can systems for the SV650 on the market don't seem to pay much attention to flow/performance and instead focus on aesthetics and sound.

Correct, the flow is worse than the OEM and a lot worse than performance 2-1 systems.

It is all for looks, no real performance has been gained by these systems (at least never repeated on anything other than seen on Renegade's dyno). Also there is added weight with no gain.