Separate exhaust pipes

[Twitchy]

So I was shooting the breeze with a mate on the weekend, comparing notes (he has a TL1000S - I think he likes my VTR and wants one but doesn't want to copy), and the idea of the exhaust pipes being split into 2 totally separate and individual systems. Has anyone ever come across this or thought about it? Delving into serious territory here - "why bother", "it works just fine", opening a jetting can of worms" etc etc. But this is the house of OCMD, this is who we are, this why we are here, and this is what we do

But seriously, why does the exhaust system need to connect? With a 270 and 450 degree ignition, and what looks to me like two different lengths to the connection point, is it possible at some point an exhaust pulse is hindering the other? Retaining the same size pipe will give identical exhaust velocity, so there should be no detrimental effects.

Interested to hear the thoughts of those great VTR minds!

[Stephan]

probably something with exhaust scavenging. Important is, that there is no v-twin full exhaust system from reputable manufacturer like yoshimura or akrapovic, without this feature.

Some reading here, search for text headline "Crossover Pipes".

https://www.musclecardiy.com/performanc ... ipe-guide/

[Wicky]

Having a dyno helps test theory

I think this vid was originally posted by Carl de dark

[tony.mon]

I've often thought about this.
If you were going to give this a try, I was going to use a "trombone slide" section and move it while it's strapped on the Dyno.
You should be able to get a quick result to see what length pipe works best.
But the crossover will take a bit more thought.

[fabiostar]

you mean as in. as if its two big 500cc singles?..not connected in any way?

i used to have an old 900 Ducati and the pipes at no point connected to each other.

[jchesshyre]

probably something with exhaust scavenging.

Yeah, I wonder if the exhaust flow in the shared part of the system from the first cylinder's exhaust stroke helps to scavenge exhaust from the second during its exhaust stroke (and obviously vice versa)?

[VTRDark]

Unless you going to do it just for the looks and to be diffrent then it's not going to be worth it without all the specialist equiptment and calculations along with dyno time required to get things right. If anyone thinks that carb tuning is a Black art well exhaust fabrication is on a whole new level.

[sirch345]

So I was shooting the breeze with a mate on the weekend, comparing notes (he has a TL1000S - I think he likes my VTR and wants one but doesn't want to copy), and the idea of the exhaust pipes being split into 2 totally separate and individual systems. Has anyone ever come across this or thought about it? Delving into serious territory here - "why bother", "it works just fine", opening a jetting can of worms" etc etc. But this is the house of OCMD, this is who we are, this why we are here, and this is what we do

Kenmoore did just that, take a look at thread here:-
viewtopic.php?f=9&t=41583&p=454487#p453466

Chris.

[Twitchy]

probably something with exhaust scavenging.

The scavenging is actually the negative pressure wave moving back up the pipe from the point the pipe gets bigger – the collector (or x piece). The wave arriving at the valve during the valve overlap period is where the scavenging takes place. However it should be noted there is actually a very narrow window where this is beneficial, as the diameter of the pipe and length of the primaries determines the wave speed and timing.

The further away the collector is, the longer it takes for the negative pressure wave to get back to the valve, i.e. the longer the primary, the higher the rpm the ‘scavenging’ affects. Shorter primaries have a greater effect lower down, longer primaries for higher rpm effect.

... that there is no v-twin full exhaust system from reputable manufacturer like yoshimura or akrapovic, without this feature.

I wonder though, if these manufacturers use the OEM exhaust as a template, make a jig, and then produce their own system with better quality materials using that jig?

As noted in this article; http://www.enginelabs.com/engine-tech/e ... nd-theory/ “When you have an exhaust header that does not have a collector, that scavenging wave hits the end of the pipe and comes back there’s an important ratio that comes into effect. The greater the area ratio, the stronger that vacuum wave is. When you have a single pipe the area ratio at the end of the pipe is infinitive because you’re opening it up to the atmosphere.” I think that is why Kenmoore is reporting a noticeable improvement – OEM size piping without a collector.

A lot of Harleys have 2 separate pipes - which I know is a big fat cruiser, but the principles are the same – and the Honda RC213V and Ducati GP bikes have the front 2 cylinders going 2 into 1, and the rear 2 cylinders going 2 into 1, as opposed to a 4 into 1 system (a little bit different but still intriguing).

I’ll keep reading and thinking!

[VTRDark]

he scavenging is actually the negative pressure wave moving back up the pipe from the point the pipe gets bigger – the collector (or x piece). The wave arriving at the valve during the valve overlap period is where the scavenging takes place. However it should be noted there is actually a very narrow window where this is beneficial, as the diameter of the pipe and length of the primaries determines the wave speed and timing.

The further away the collector is, the longer it takes for the negative pressure wave to get back to the valve, i.e. the longer the primary, the higher the rpm the ‘scavenging’ affects. Shorter primaries have a greater effect lower down, longer primaries for higher rpm effect.

Sounds to me like you have your head around the complications of it all. And then the tapers at each end to help with the smooth transition in change of direction.