sorry didn't keep my stock stinger. But I do have a little info on the subject. We have been making pipes for several years now. This article and these books have really helped out. I understand you are getting into mufflers, but pipes are where the real power is made. I bet you already know this, but handmade pipes always look knarly ! ! ! I:I
Two-Stroke Performance Tuning in Theory and Practice by A. Graham Bell 1983
The High-Performance Two-Stroke Engine by John Dixon 2005
Mind you it's out of the January 1997 issue of DIRT BIKE, but it's the basics on 2 stroke pipes. I've copied it word for word, BTW... check out the last paragraph!
"Expansion chambers are fascinating. The look cool. They sound great. They
are mysterious. Everybody knows that, somehow, these non-moving parts are
responsible for quite a bit of the mind bending power today's two-strokes
crank out - but hardly anyone knows how they work.
So, for readers with a healthy curiosity about bulbous sheet steel two-stroke
exhaust systems, we present the following pipe primer.
ECHO WHAT TEACHER SAYS
Basically, and we mean basically, expansion chambers are shaped as they are
so that they reflect sound waves back at the exhaust port to hold the
burnable charge in the cylinder. Without the expansion chamber, a large
amount of power producing fuel and air would escape from the exhaust port
because the exhaust port must be open when the fresh fuel/air charge rushes
into the combustion chamber. Four-strokes don't need two stroke type
expansion chambers because they have valves that seal their exhaust ports
during the intake cycle.
Though each section of an expansion chamber has its own areas of influence on
power delivery, it is important to point that no section of an expansion
chamber works entirely independently. Of the others. Any change in length,
shape or volume in any part of the pipe will bring about changes in the way
the pipe affects performance. Generally, changes that hurt performance in
one area will boost performance in another, but it is possible to make
changes that only hurt or help performance. Skilled pipe manufactures seek
out changes that are most beneficial through time-consuming track and dyno
testing.
GO TO THE HEADPIPE OF THE CLASS
Perhaps you have noticed that the first sections of today's expansion
chambers are tapered and that some pipes use straight-tube head pipes.
Tapered head pipes are relatively more difficult and costly to manufacture,
so they are rare on non-race machines. Tapered head pipes have proven to
boost performance and ease pipe tuning in their main area of influence - low
to mid rpm power - has proven to be best for most racing applications.
In general, a relatively longer head pipe will bring about more bottom-end
power at the expense of peak power. A short head pipe generally brings on
stronger peak power and subtracts bottom-end. That's why pipes on trials
bikes have very long head pipes and those on 80cc motocross bikes are short.
I LIKE TH E CONE BEST
The length, volume and taper of the first cone strongly influences the amount
of peak power the engine will produce. A relatively short, steeply tapered
first cone, as on 80cc motocrossers, creates high peak power with sacrifices
at other engine speeds. Pipes on Open-class bikes usually have gradually
tapered first cones because smoothness, rather than peak power, is of more
benefit.
BELLY DANCING CLASS
A pipe's midsection is where length or volume adjustments are make to
compensate for less than "ideal" head pipe, first cone, final cone and
stinger/silencer dimensions that can't be used due to the size and shape of
the bike. The pipe's midsection or "belly" can be enlarged, shortened or
lengthened to bring about the same results as most "ideal" designs.
STUDYING FOR THE FINAL CONE
Anyone who rides will tell you that what happens after and engine's power
peaks is nearly as important as the peak itself. Controlling power after the
peak, the overrev or overrun is the final cone's job. A relatively longer,
gently tapered final cone will give you more overrev. A short, steep final
cone gives you less. Why not go for lots of overrev? You will lose too much
top-end. Getting the picture? It's pretty much all give and take.
ANSWERS TO THE POP QUIZ ON STINGERS
The tailpipe, or stinger, is as important as any part of the pipe. Its size
and length influences peak power and bottom-end, and can even affect an
engine's resistance to holing pistons.
In general, smaller stinger diameters create more peak horsepower but
increase the likelihood of melted pistons because they bottle up the exhaust
heat. Big stinger diameters boost bottom-end at the expense of peak power.
Excessively large stinger diameters can hurt performance at all engine
speeds due to insufficient back pressure.
Stingers length is important, too, because it's part of the total pipe length
and volume. Generally, longer stingers help low and midrange power. Why not
run a long, large diameter stinger? The pipe has to fit on the bike!!!"
Good Luck with the testing, It took two months till I found the dimensions for my CR500R. In the end it was well worth it.
