greetings again 2 stroke fans and welcome to all new subscribers hope you
get something in these videos. At the moment this series covers two-stroke
expansion chambers, the secrets of them and I'll explain that in time but
another objective is giving you enough basic information so that you can make
choices looking at expansion chambers and doing modifications to your own ones
without going into too much science because there is some fundamentals. So
far we've done a couple of videos I suggest you go back over those I will be
referring to. In the previous video we covered the subject of measuring the
expansion chamber and the lengths of the actual cones using a formula by
putting a ruler down the side and I'll jump into the software shortly and show
you those calculations that I've done and I've been a little bit of messing
around there as well we'll get into that. first. So that's
the length of our actual components in relation to our tuning length so lengths
here relates to the timing of when our waves arrive at certain rpms and
calculation of the diffuser cone actual total length of the diffuser cone and the
angle of the diffuser cone. So as we know a higher angle will give us a
higher signal of a shorter duration and a lower angle will give us a longer wave
of a lower amplitude so to calculate the length of the wave that we want because
that will be tied to the RPM as the RPM rises the arrival of the of the wave at
the right time we have to know the actual length length of the wave and
what RPM range it will be useful in keeping in mind the diffuser gives us
our range of power up to our peak okay where the baffle cone is at our peak and
above this is up to epic so this is the longest range of operation of our engine
the main curve now we need to know what the minimum makes it what the minimum
and maximum are that range will be and for that we need
to know the length of our wave, now if we know the length of our initial wave that
comes out of the exhaust and then we know the taper the angle the length of
this the total length of this we can work out what the length will be of the
reflecting wave that comes back and it basically comes down to basic megaphone
calculation which is that the the smallest end is the highest rpm range of
the diffuser and this and the largest end is the lowest rpm range of the of
the diffuser now in more complex ways we can calculate the wave, the original wave
length and pressure from the wave and we can do that by translating the blow down
time that's the time between when the exhaust port opens and then the
subsequent transfer port opens that's the blow down period we'll determine the
amount of time that our original wave is so knowing that we can calculate the
maximum rpm where the head of the wave will be reflected okay at this end and
then the minimum RPM the wave will be reflected and then plus the wave itself
the wavelength itself, so going from the start end to the start end, so
if we were looking in expansion chambers from the point of view of deciding
whether we got two pipes that fit the one bike and which one is going to do
what, we can have a look at expansion chambers with multi tapers or even
curved like a top of a wine bottle neck curved parabola curves in a pipe and we
can assess what's going on by looking at the ends of the pipe, if
we've got a slow taper at this end of the pipe and in the taper is high at
this end of the pipe well it means we're pulling a strong wave at the lower rpm
range okay, and when it gets to the high rpm
range we've got a very shallow angle so the strength of the wave won't be as
strong at this end as it will be, (now remember this is in timings okay)
as it will be in lower rpm, whereas if we've got a pipe like this one which has
got a steeper angle early on okay and it might be a three-stage or or this type
can diffuser that has a higher angle here and then has lesser angles here
okay not less than this but just not as steep a gradient
okay, that means we're getting a stronger single signal at our higher rpm's and
then not as quite as strong and our lower rpm's, so a pipe with a with a more
higher angle earlier on in the diffuser and then not so much late in the
diffuser is better for top-end power, and then a pipe with an angle
that's nice and narrow and down at the starting of the diffuser and then gets
steeper quite a bit by the end will be better boosting in the diffuser section
for low end power, so that's how you can tell simply by looking at the pipe,
tapers to determine what the characteristics of the pipe are going
to be basically. Now in later pipes we get into this type of design okay and
designing the ratios of these as in what distance this one has to be from this
one and this one okay, we've got to divide this up into into like a
percentage of ratios so it's a percentage of whatever the full length
of the taper is compared to a single taper now what we use basically is a
calculation which is kind of like a a horn it's called a horn coefficient and
what it does is it gives us the actual degree of exponential curve so if you
want a more exponential curve that's curves like this okay then we use a
higher coefficient and then allow our coefficient will be just give us a
lesser sweeping curve up there and then what we do is we plot points at
percentages along that point and then we get thus we derive and this is trying to
be but basically this okay but it's just in three stages.
So that is in design software okay to design a pipe but from our perspective
when we haven't got design software so we're just looking at what the actual
diffuser does in the pipe that we've got and then what design changes we might
want to make like we might want to use a diffuser a different type of diffuser
and make a different one so what we could do is we could essentially use the
same diameter points along here the percentage of the diffuser and then we
could increase the angle here a bit and have these angles lesser and we have a
pipe that operated it a little bit higher in the RPM range, that's just an
example okay, now that again gets down to the
slope of the tapers and the wave slope so that's where how our slopes are
affecting our range okay and we can calculate the wave lengths and so forth
for the timings for that and we can actually find out what the what the
amount of time our wave lasts for and accurately enough and then the next
thing is our diameters and diameters is determined by relationship
to the port width and the height so the port area of the port window okay, now if
we were designing our own pipe it would have to include the porting all those
dimensions are taken from the relationship to the port window okay, now
I'm gonna get into. We are up to eight minutes now so I'm gonna delay
this until the next video and we'll get into how the diameters are determined
here and neutral chamber diameter and the outlet pipe diameter and I also want
to show you some "didlings" in the software that I've been doing, and that'll
do it for today. Okay, I'll see you in the next video