exhaust expansion chamber

A little way past the foot peg put about 2-1/2" tube about 11" long then taper to about 1.125"

Expansion chambers are used on 2 stroke motors. Your specs are for a 4 stroke. For a four stroke, a straight pipe with a low-restriction silencer works fine.

generally true.

I highly recommend that anyone truly interested get a copy of Smith & Morrison's Scientific Design of Exhaust & Intake Systems , it's a bit old & shows rather quaint test instruments, but the basic principals are an ideal place to start.

One thing to keep in mind: if you tune for maximum power @ max RPM, you'll rarely have what you really want. For road or circuit-racing, a sacrifice of peak power to broaden the curve is worthwhile.

As Blink stated, expansion chambers are used on 2 stroke motors. Beyond that the exhaust system is receptive to many variables. First thing that comes to mind is what RPM do you want power? Longer, thinner pipes help low end torque. Short fat for higher RPM. What length and diameter is the intake? Carb, or injector air inlet size. There are so many variables that I would suggest you get a look at other bikes that are used the way you want to use yours. What are the exhaust systems on those bikes. Copy what you see. Then experiment. Go longer, go shorter, go smaller, longer.

Back in the sixties I read an article on custom exhausts. It stated that a collector extension should be left much longer than calculations call for. Paint them with cheap paint. Then run the car hard. Then cut off all of the extension that the paint did not burn off of. I don't think it would apply on a single cylinder, but it could not hurt to try. Please keep us posted. Good luck.

We always used chalk and cut where the burn started for placement of collector about 18" pre to cross over tube.

Wow did you the mark. Of the twenty or so custom exhaust systems that I had built for fellow car nuts, 18" was the most common length before reducing the collector. Your figure confirms that I was at least close. Thank you.

There used to be a term "expansion chamber" applied to 4-stroke-cycle engines;

it consisted of an exhaust enlargement very near the valve, larger than either the port or the pipe.

Function: soften the exhaust 'pulse'

Purpose: some combination of sound attenuation & reduction of wave peakiness in tuning.

In all honesty, i've never actually seen one in 30+ yr of playing this game, just 'heard' of 'em.

As Bob C stated, Plagarism is usually an excellent starting point.

The major variables he did not callout: Camshaft timing, Speed of sound in the pipe, & exhaust volume/ cycle.

to expand-

Cam timing; determines when the best point of arrival for the negative phase of the wave will be

Speed of sound: effects wave action period; atmospheris pressure mass, of exhaust products, & EGT play here.

Volume: really Mass + resistance in pipe; methanol based fuel will have more massive exhaust.

MEGO, too!

My recommendation: if the 'hot-dog' in your arena is utilising a similar arrangement; copy his, then vary +/- 10% his lengths, i one shows promise, try another 5%, ad. infinitum

Variable diameter piping adds strength to the returning waveform; if you're correct length, it should help. Wrong= worse. Bad seems to hurt worse than Good helps.

Stepped pipes are in vogue now; longish tapers seem to return stronger wave action

Very good. How much of an effect do pressure waves have on single cylinder engines? My experience has been with automotive engines only. I thought the negative pressure waves would help to draw the exhaust from other cylinders. How does it effect a one lung?

Have you seen the exhaust collectors being used on NASCAR lately? They have a funnel like device that is just behind where the separate pipes merge into the collector. They look like they would restrict exhaust flow.

Tuning 1cyl pipe has a purer input signal; still uses 'waves' to work, inertia waves are stronger (mass of air, using itself as spring) than sonic waves. Narrow range pipes will try to use both.

Funny enough, the 'nascar' collectors you refer to are called merge collectors! Used to increase speed of gasses; higher velocity gas has more inertial energy. The constriction also acts as venturi, reduces pressure as it speeds up flow.

good anszers by mr. bobc and sidevalvedude.thx.how do i find out the speed of sound in the pipe?will it be the same after mods.how do i allow for any changes in speed?

also i see that the chamber has to be tuned for a specific range.how large can this range be and what will the effects of longer or shorter rpm range be.if the answers require me to read up by myself p[ease point me in the right direction.

as you can see from the specs its not a particularly powerful engine we just need to squeeze as much power as we can from it.

http://search.barnesandnoble.com/booksearch/results.asp?TTL=scientific+design+exhaust&ATH=&WRD=&PRC=&FMT=&AGE=&CID=

Speed of sound will vary w/temp, constituents, & density. Bigest factor here is changing throttle position.

The 'chamber' usually takes the form of a 'reverse cone' megaphone, if non-silenced exhaust is permitted. Usually ~0.5-1. x headpipe length; 2-4 x headpipe diameter. The steeper the angles, the stronger the returning signal; for good OR bad.

Follow on to my previous:

EGT relative to throttle position; if you're not at WOT, you are more interested in economy. EGT will vary with engine load at WOT.

Just took a closer look at your specs here.

8.5K RPM seems a bit slow for an engine this size; what is your application?

i never said 8.5k rpm.. its a economy bike engine ( fuel economy).i woud'nt know how to explain to someone who isnt from india or my economic class what the purpose is.i need to know how much i know+ how much i can learn on the basis of that without ruining the motor.i need it to go as fast as poss.thats the aim for the current time. i am not ashamed to say i have no idea what you said in the second ans(continuation to ans 1).but ill do my best to learn.max power = goal even though engine = stupid.

My understanding now is that you want 'fast road transport' in the original motorcycle.

Is your primary useage in city, mixed(city + rural), or rural?

Always try to reduce losses.

Keep an eye on your chain; if poorly lubricated it will consume a great deal of power.

O-ring chains tend to be stiff, i prefer plain; lubricating daily between the side plates.

If most of your riding is on acceptable pavement, a semi-slick tyre might help; knobby types use a lot of power flexing rubber. (On the flip side, better traction with a trials type knobby might give you the confidence to go faster)

If this m'cycle is used primarily in an urban application, i'd try a rear wheel sprocket with 2-3 teeth more than stock; this will make the unit much quicker (as opposed to faster, which will suffer a bit)

If the factory exhaust came as a 2-piece unit, i.e. headpipe + muffler; i'd try varying the headpipe length by +/- 15mm. Then try increasing the diameter of the 'best length' by 2/3mm. That should give you a pretty fair approximation of 'the best' pipe; the manufacturer couldn't have missed by much.

8.5K RPM is the maximum power rpm as stated by the engine spec chart; for purely 'speed' you'll want to be very near that point. Unless, by camshaft replacement & electronics modification, you can raise that.

"what you said in the second ans(continuation to ans 1)" What i meant here is: unless you're at full open throttle, you are in a driving mode, & want best fuel useage; if all you wanted was more power, you would open the throttle more.

However, my current read on your question is: "i wish to go quickly from point A-B (acceleration=exhilaration= fun!); i'm a normal guy - keeping a family together takes most of my resources"; please be assured that (probably most) many of us have similar situations.

really sorry that was a misprint in the spec chart.the real power range (i'd love to hear what you have to say now since you thought 8.5k rpm was too low) was 5.5k rpm.6k for torque.i pay decent attention to lubrication allready.i never knew sprocket calc. was as easy as increasing 2-3 teeth.i was using a formula to calculate power transmission that i cant recall right now or gear ratio calculators availible online.anyway i have come to the conclusion current engine is not right for modifications so im gonna leave it alone.

searrching for new ride now so this discussion is closed unless someone wants to just discuss the concepts which would be nice.thanks for the book link ill let you know as soon as i find the illegal pdf version online :)