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#Post#: 70614--------------------------------------------------
Re: intake/crankcase stuff
By: 1manband Date: March 25, 2016, 2:46 pm
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i will post up the basic res program up in a bit. it varies a
slight bit from what was presented in the K&W paper, because i
not not going to spend 3 hours
working out the difference in case volume between 90 and 120
degrees for this in a program, nobody is going to use anyway.
there are no motor secrets. all this kind of thing was figured
out 30 to 60 years ago.
(it is not a big difference at all, you will find this out when
you plug in differing volume values).
side note: it will help to approximately determine a case size
for rpm.
imagine, that it would get folks close enough, but just like
exhaust, would need some cut and try....just like every exhaust
formula i have tried,
there is not pressure variable within the formula, and
approximated by sound waves.
think some other formulas that make corrections and such would
get closer with less cut and try. will be looking into that
shortly.
#Post#: 70615--------------------------------------------------
Re: intake/crankcase stuff
By: 1manband Date: March 25, 2016, 4:03 pm
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just trying to unravel some things i have interest in.
hope it helps.
tiny program below. save first, then extract, then should be ok
for use.
#Post#: 70618--------------------------------------------------
Re: intake/crankcase stuff
By: 1manband Date: March 25, 2016, 5:38 pm
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link to 64 page scavenging/helmholtz paper by engelman. i
mentioned before. long intensive read. about page 50 or so.
4. engelman
HTML http://minds.wisconsin.edu/handle/1793/396?show=full
#Post#: 70620--------------------------------------------------
Re: intake/crankcase stuff
By: 3000 FPS Date: March 25, 2016, 9:24 pm
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Just so happens I am a guitar player. I do find this all very
interesting but it is more about the theory for me than the
math.
When I studied electronics and we were discussing resonant
frequencies and showing them on a scope, I don't remember but
can there be more than
one resonant frequency or as in the case of a guitar more than
one harmonic. Its been 40 years since I studied that stuff.
But hey I still find it interesting to read. I do not leisure
read and only like to read tech stuff.
What I was really interested in seeing was what your finding
were and what effect porting a saw had on the pressure waves for
the intake. To me it looks like it may help it more than hurt
it.
#Post#: 70623--------------------------------------------------
Re: intake/crankcase stuff
By: 1manband Date: March 26, 2016, 6:16 am
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[quote author=3000 FPS link=topic=5779.msg70620#msg70620
date=1458959061]
Just so happens I am a guitar player. I do find this all very
interesting but it is more about the theory for me than the
math.
When I studied electronics and we were discussing resonant
frequencies and showing them on a scope, I don't remember but
can there be more than
one resonant frequency or as in the case of a guitar more than
one harmonic. Its been 40 years since I studied that stuff.
But hey I still find it interesting to read. I do not leisure
read and only like to read tech stuff.
What I was really interested in seeing was what your finding
were and what effect porting a saw had on the pressure waves for
the intake. To me it looks like it may help it more than hurt
it.
[/quote]
same here.
imo, at this point, the potential benefit of using this concept
is debatable in a saw motor. i am not saying that it does not
work, but that it most likely has already been incorporated in
the motor when it was designed at the factory for a particular
rpm.
in example, looking at my jonsereds 52. the specs i found say
that maximum HP happens at 8300 rpm.
running the numbers, came up with 8900 rpm for the resonant rpm.
the formula is an approximation, also has some generalizations,
not taking in temperature, heat, pressure, pipe end corrections,
etc. even with all that, is roughly 600 rpm off. maybe it is
a wash? don't know. not sure if this is the rpm to shoot for
anyway.
would tend to think, that in order to truly maximize the
potential of this concept, the porting goal would need to be
made for a specific rpm in mind.
since, the intake hole size is also affecting the "tuning" of
the case.
even reducing the case volume a good bit, has a small effect on
the formula results like rpm for the numbers i ran.
do believe, that everything can work together to achieve the
greatest benefit, and has to be balanced to work well.
i enjoy reading the tech stuff, and wondering if it can be
applied to help these tiny motors. usually my interest gets the
better of me, and spend time
chasing my tail or running into dead ends. but, hope folks
could at least learn from my mistakes.
#Post#: 70625--------------------------------------------------
Re: intake/crankcase stuff
By: 1manband Date: March 26, 2016, 7:05 am
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during my web finding research, there is very little out there
on two stroke intake tuning. for every 25 web search findings,
maybe 1 or usually none in regards to 2 stroke findings.
remainder for 4ST's.
it was not my focus to look into 4ST's, but did read about quite
a few. i only mention this in passing.....and will suggest that
some homework on these is done and the realistic rpm of daily
driving scenario is considered. there is quite a boat load of
information out there, and some of these setups can get pricey,
at least for me anyway.
#Post#: 70631--------------------------------------------------
Re: intake/crankcase stuff
By: 3000 FPS Date: March 26, 2016, 10:05 am
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Thanks for the info.
#Post#: 70674--------------------------------------------------
Re: intake/crankcase stuff
By: 1manband Date: March 27, 2016, 9:50 am
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looked into the looming question of intake port cross sectional
area as it relates to both porting and crankcase volume.
did this by using both the time*area program and the crankcase
res program.
went like this:
in the t*a program, wrote down the intake port t*a value and
port area for the stock example saw. 0.00013539 sec cm2/cm3 and
0.428 in2
then, raised the stock 5500rpm (@peak tq) value by 2000 rpm.
(as rpm goes up, t*a values get smaller). 0.00009928 sec
cm2/cm3
so, to raise the peak torque rpm, by 2000 rpm to 7500 rpm......
you would need:
0.00013539 (-) 0.00009928 = 0.00003611 <that much more t*a
then adding that result back into the stock number:
0.00013539 + 0.00003611 = 0.00017150 <this becomes the time*area
goal, to get the 2000 more rpm.
keeping the t*a rpm, at 7500, i changed durations until the t*a
for the inlet port was close to 0.00017150 sec cm2/cm3.
the area of the intake port needed to get this goal t*a was
0.496 in2.
finally, (all this took all of 5 minutes), plugged the 0.496 in2
inlet port area value into the crankcase res program.....to see
just how close, the rpms would be by changing areas........
<edit> added screen shot of error or difference.
#Post#: 70675--------------------------------------------------
Re: intake/crankcase stuff
By: aclarke Date: March 27, 2016, 9:56 am
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Joe,
Are the TA number above based on your modified Blair/Jennings
numbers?
#Post#: 70679--------------------------------------------------
Re: intake/crankcase stuff
By: 1manband Date: March 27, 2016, 11:29 am
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[quote author=aclarke link=topic=5779.msg70675#msg70675
date=1459090614]
Joe,
Are the TA number above based on your modified Blair/Jennings
numbers?
[/quote]
nope. the numbers from the program posted in other thread. if
i'm understanding the question correctly?
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