Pipe and a can?

[Black Knight]

This might be a dumb question but what exactly is the function of an exhaust system, how does it work and how does it boost power???

I'm don't want to even touch on 2 strokes just stick with the 4 for now!

There are so many different designs on the market I can't see the logic behind it.

Does the shape or size of the can make a difference? How? the lenth and design of the pipe??

From straight through pipes on the choppers to none at all, to 4 into 1's, 4 into 2's, 2 into 1's, race systems, one off peices, big fat cans, designer downpipes (buell), gas ports (blackbird). Does anyone know the science behind it?
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Where does a turn end? 'Where you can do anything with the gas you want to, where you are brave again, where your attention is free from the turn, where you are sure you can do it better next time; that's the end' - Keith Code.

[Kickstart]

Hi

Can itself is pretty much just there to reduce noise. Most modern stock systems are very good at doing this with minimal reductions in power. There is nothing magical about a race can, it is just a perforated tube surround with some packing material to have some vague attempt at reducing the noise.

Main part that is there for power is the down pipes, with the order the pipes connect and the lengths being very important. And it is a hell of a lot more complicated than I understand.

All the best

Keith
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[mr.z]

As i understand it.. (correct me if i'm wrong)

The pipes/lengths give the exhaust gas a certain ammount of back pressure, giveing the "optimal" ammount of backpressure at xxxx rpm shorten/lengthen the route of the gas flow and this will alter the backpressues optimal point.. this is where increace/decrece of "midrange/topend" comes in..

Ideally an exhaust wqould be infinitely varyable to open/close as revs increace/decrece.. (some have a system with a valve, can't remember the name of it, yamahas though?)

Tis more important with 2strokes as backpressure helps hold the mix in the cylinder, to which point it would barely run if the exhaust was taken off.. (which acocunts for the huge power stompy powerband) (look on how stuff works.com and search 2strokes)

As has been said the cans main point is to bring the exhaust noise to an acceptable level, which inevitably restricts gas flow, take the can off the gas flow increaces, but this will draw more air through and carbs need to be adjusted to suit, otherwise lean running is a risk (but if the air filter is restrictive enough it might make as much difference, take the can off and air filter out then you'll have a hell of allot of noide and a huge ammount more fuel squirting through)

Hope some of that makes sense and is vaguely correct..
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>RidingSkills<->Tech Tips<->MyBikes<

[MarJay]

An Ideal exhaust would employ pressure waves to draw exhaust gases out of the exhaust valve when it is open... this has to happen for each cylinder as it is in its exhaust phase. if the pressure wave is wrong (IE back pressure at the opening of the valve) then the exhaust gases do not escape easily as they are pushing against the pressure wave coming back along the pipe.

This is easy to manage at a fixed RPM but harder to do across the whole rev range. Hence the EXUP type valve.

Two stroke expansion chambers do a similar thing to two strokes hence they are very quick when 'on pipe' and sluggish when not. Hence YPVS Etc.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[Misc]

A slip-on on my bike makes a very big diffrence, it now runs smooths & doesn't jerk back as much at top speed plus slightly better performance.

[0ddball]

It can't be explained well in one post, you can fill a good sized book with just exhaust tuning theory.

Put basically a well designed one boosts power by working like an extractor fan. It literally sucks the gasses out of the cylinder. You never get rid of all the exhaust gases on a normal road going engine because of the tame cam duration and lift, there is always some dilution of the inlet charge (air/fuel miture). But a good system will minimise this dilution. More room for fresh air/fuel miture means more power.

The length and diameter of the pipes are important because you want the pressure waves created by the opening and closing of the exhaust valves to compliment each other rather than cancel each other (remember the wave tank interference experiments in physics class).

The can is still important but not as important as the downpipes. Generally, the closer you get to the engine the more important the exhaust component is because the gasses are hotter. The main aim is to keep the gasses as hot as you can untill they exit the tail pipe. The hotter they are the faster they move and the greater scavenging occurs at the cylinder end.