Yamaha TRX850 Enthusiasts Forum

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Looking at aftermarket systems they all seem to link with a balance or have a collection box as per a 2 into 1 system at or around the same distance as the std Trx headers. Even the Akrapovic 2 into 1 has a small link at that point but collect at double the distance. So there must be some purpose for this measurement with the pulse and flow..

I am preety sure mine doesnt have a link pipe, Its a home made large bore (not made by me) It all seems to work ok. Its just for track use at present. Dave

Edit... I'll have a look at it tonight as i am having doubts as to wether there is a link pipe or not. Will update later.
IT DOES HAVE A LINK PIPE SORRY FOR MISLEADING YOU.

From memory it is about speeding up the flow of exhaust gasses and controlling back pressure. It has something to do with allowing each cylinder to see more header volume than if the balance pipe wasn't there. The placement will vary a bit depending on the header diameter and shape.
Once had a discussion with an exhaust guy about it, but it got quite complex and lengthy and we both had more than our share of Jack Daniels finest.

I was wondering what to do with my lunch hour................

Have read that some modern engines tee off the exhaust system at some location to pull a negative pressure on the crankcase thus reducing power loss due to +ve case pressure. Think the 2005 ZX10R has reed valves in the crankcases relating to this?

May be that exhaust gas passing through one header pulls a reduced pressure within the other pipe (Bernoulli principle?) and this encourages emptying of the second pot on the exhaust stroke?

Thanks to Wikipedia;

In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.

Bernoulli's principle can be applied to various types of fluid flow, resulting in what is loosely denoted as Bernoulli's equation. In fact, there are different forms of the Bernoulli equation for different types of flow. The simple form of Bernoulli's principle is valid for incompressible flows (e.g. most liquid flows) and also for compressible flows (e.g. gases) moving at low Mach numbers (usually less than 0.3). More advanced forms may in some cases be applied to compressible flows at higher Mach numbers.

Exhaust geometry is without a doubt a complex area (and I know very little/nothing about it!). If Akra have one then I reckon it's best to have it there.

Several modern engines have reed valves thru which air from the airbox passes into the exhaust for emmision reduction (tdm for example). This system can be modified to provide some crankcase vacuum. I have a similar system on my TRX.

Similar principals apply to sub, low ,mid speaker box porting and tuning . Size and placement of ports and length to tune the box to certain frequencies. Just like the crankcase pressure as the speaker cone pushes out then returns back in this forces the air back out of the cabinet through the tuning port. Different positions , lengths and sizes tuning the box to boost certain frequencies. Roll up a piece of paper into a tube and slide it into your home speaker cabinet port and slowly pull it out and you will hear a change/boost in lower frequencies ( around 80 to 200htz ) the further you pull it out or in. Harmonics to these frequencies are also affected so its no different by changing the link pipe position. A mate gave me a bit of a run down on his (friends) when tuning Harley motors the same principal apply and you will notice different systems with different length and link pipe positions to give different power outcomes from the stock system. Bit like tuning the bell mouths on your carby intake with shorter or longer to give you optimum rev range.

Sorry for confusion, my bike does have a link pipe.
Dave

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Sounds good to me. Keep riding it and keep enjoying riding it

Mark.

While 5 of us went for our Nerang ride last saturday , low and behold while we where having breakfast at Cunungra ,there goes Torino's TRX zooming past. Certainly has a sound all to itself for a TRX..

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Add this to your thoughts on pipes…….ready….. the gas that pass through the exhaust (and inlet) has a mass which means that it will also have inertia and it takes energy to move this mass and to stop it….also as you heat any gas it will expand and increase in volume, the gas need to go somewhere and that is usually out the muffler, think of a boiling kettle the hotter the water gets the greater the pressure of the gas (in this case water vapour, simplified).

Still with me now when the exhaust valve opens the cold intake air has now become hot (expanded) and increased in volume, this explodes out of the head past the valve, the shock wave created is travelling at the speed of sound (340 M/S) you can feel these "pulses" at the muffler tip.

Now sound is a funny thing, as it will resonate (vibrate) most things (given a high enough frequency). The total exhaust system is made up of many different components which all resonate at a different frequency, straight lengths, curves, joints, mufflers, diameter etc. the larger the total volume of that section the greater the resonance and so the greater the pulse

Now the pulse (explosion) will travel down the exhaust and as it passes each different section, that section will resonate and as the pulse passes into another section a small (depending on the length of the section) part of the pulse/resonance will reflect back the other way. This will bounce back and forward reducing to nothing, all at the speed of sound. These pulses also compress the "standing gas" in the front of the pules adding to the fun! for a later day.

Now what would happen if a large pulse (followed by another and another) arrived at the exhaust valve at the same time that the exhaust valve opened and that pules exited? Well it wound hinder the release of gas (expanding now in volume, mass and speed) from the chamber and may even restrict it enough that not all gases can exit before the valve shuts, also not allowing the full charge of fresh air/fuel to enter the combustion chamber (remember this is happing at the speed of sound) not good. Note: this will only happen at a certain RPM, we have most likely all ridden bikes that had a serious flat spot or drop in power at a fixed RPM, well this can be the cause, as well as many other things, but this is the feeling from the engine that you can get.

Still with me can we use these pulses to our advantage? Shit yeah Batman! We can create an exhaust that has the largest pulse impact the exhaust valve milliseconds before the valve opens and as it returns down the exhaust it leaves a small vacuum behind it creating a negative pressure zone, which helps "pull" the gas down the exhaust. Better off known by the masses as "exhaust scavenging".

If you have bought a "designed" (engineered) exhaust system it will have been created to have sections that will absorb these pulses and other sections that will create large pulses, creating a system that can flatten out the torque curve (street) or even enhance the torque at a known RPM (drag racing).

What does this all mean to us, well different systems will enhance the power/torque at different RPM to suit track or road, so not all systems are equal. If you put a race system on you bike with a street muffler this may be of a disadvantage on the road or track. Will you notice the difference between two aftermarket systems….maybe….. but most people don't trial several systems before deciding on the one that suits their riding. But a race team will have several systems to suit different tracks and/or different altitudes, fast open at sea level or tight low top speed at altitude.

Balance pipes are created to suppress these pulses and are usually fitted at a known point in the pulse and smooth out low speed response.

The greatest issue with exhausts is that most people are going from a "restricted" factory system to a free flowing system and anything is better than the factory system. So no matter what they fit it is always ( ) better. If you mapped the torque and HP before and after you fitted an average system you will see the improvements, but, not what could have been with a quality system!

Long live the fettler

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