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#Post#: 70501--------------------------------------------------
intake/crankcase stuff
By: 1manband Date: March 22, 2016, 3:11 pm
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looking at the some of the papers, many state there is benefit
to fooling with lengths, x-sect areas and volumes.
hope to get into some different ways to figure this out.
i enjoy working design numbers if y'all haven't noticed.
maybe just more of my digital garbage, don't yet know myself.
number/graph phobia folks........shield your eyes! hahaha.
#Post#: 70507--------------------------------------------------
Re: intake/crankcase stuff
By: 1manband Date: March 22, 2016, 5:38 pm
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ok, this is the science end of it.
screenshot shows the idea.
frequency is expressed as "Hz" and is how many waves pass by the
same location point in one second.
think about it as a piston moves up and down in the cylinder.
as rpms increase, piston moves more times per second, same idea
as waves and Hz.
everything i do in the thread will be done with references.
before anybody says....."but there is a transfer port too."
"what about that?"
in a paper on delivery ratio, by komatori and watanabe....they
state that the intake is not affected by the previous
cycle......page 11.
paraphrasing their words not mine. and that's how the rest of
my blabber will be written whether i agree with it or not.
#Post#: 70508--------------------------------------------------
Re: intake/crankcase stuff
By: 1manband Date: March 22, 2016, 5:54 pm
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above reference was from georgia state university. great site.
search >sound waves>resonance>cavity resonance ......and you
will find it.
plodding along, some motor books and magizines and other things
use this formula to find resonance in intakes and such.
the delivery ratio paper i noted for 2 strokes uses this as
well.
cool feature on the georgia state U site, it can calculate all
this for you if you just plug in your motor measurements. it
also has a temperature correction feature if you decide to add
that in as well. just make sure you use the same units of
measure.
since i am using the paper, if you plug in the values they list
on page 11.......you will also find out that they made a boo
boo. enough about that. <edit: will look into that again, has
got to be something i missed.>
paper is great info.
#Post#: 70509--------------------------------------------------
Re: intake/crankcase stuff
By: 1manband Date: March 22, 2016, 6:01 pm
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more in a bit.
#Post#: 70514--------------------------------------------------
Re: intake/crankcase stuff
By: 1manband Date: March 22, 2016, 7:29 pm
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that GSU calculator is cool.
couple of things that i ran into, that may save some time.
just a note, to help if you use the online tool.
in the paper, they use the 'mean' crankcase volume. this is the
BDC volume of the crankcase + 1/2 the swept volume.
if you do this by hand......
from the paper they use, c = 1100 ft/second. if you work it out
by a handheld calculator, use 13200 inches/second to match the
other units, or the answer will come out wrong.
next will work out a chainsaw motor to see what it is.
#Post#: 70518--------------------------------------------------
Re: intake/crankcase stuff
By: 1manband Date: March 22, 2016, 9:02 pm
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jonsereds 52......this motor never stops amazing me. good
stuff.<<<edit: not as good as i thought.>>
hits twice.<<<<<edit: just once>>
<edit> after warning you guys to watch the units, i did not.
plugged in 118.5 cc's for case volume, it should have been in
cubic inches... 7.23 in3
changed the screenshot to reflect this.
#Post#: 70520--------------------------------------------------
Re: intake/crankcase stuff
By: 3000 FPS Date: March 22, 2016, 9:51 pm
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So what do most chainsaw engines require. Are the intakes
close in length and port opening to be efficient as they come
stock or would adding length to an intake help with the resonate
frequency or opening of the port. Also when you port a saw
that is showing RPM's of 9000 in the cut, and because the larger
port has now dropped the resonate frequency does this come
closer to that 9000 rpm or further away from it.
#Post#: 70523--------------------------------------------------
Re: intake/crankcase stuff
By: 1manband Date: March 23, 2016, 12:05 am
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[quote author=3000 FPS link=topic=5779.msg70520#msg70520
date=1458701495]
So what do most chainsaw engines require. Are the intakes
close in length and port opening to be efficient as they come
stock or would adding length to an intake help with the resonate
frequency or opening of the port. Also when you port a saw
that is showing RPM's of 9000 in the cut, and because the larger
port has now dropped the resonate frequency does this come
closer to that 9000 rpm or further away from it.
[/quote]
take another look at the screenshot roger. i fixed an error. i
got a little wowed by the previous erroneous result.
what would be ideal is have the motor work like the way those
two guys explain. waves have peaks and valleys. thing, or goal
would be to get the peaks and valleys of the waves to do what
you want at a certain rpm. both the intake and transfer ports
need different things to work well. during the initial portion
of the open duration of the intake port (when port just starts
to open), a big valley is good. during the latter portion, of
the transfer duration phase (just before it closes), a peak is
good.
if the peaks and valleys happen at the wrong time, they do not
help. to make things worse for tuning is that the "goal" is a
moving target because it changes with rpm.
in the paper, they have some ....lots of graphs. the page that
explains this better than i ever will is page 11. the graph
shows what is good and bad, with changing rpm. tomorrow will
put some notes on it, hope it will help. once you see it, you
will see it.
****<<<EDIT......this is wrong>>> IMO......in order for any of
this resonant tuning to really help, it needs to be within the
actual rpm range the motor can spin at. the 'natural
frequency'......the one i called RPM at Hz is really the one
that needs to be within this rpm range. END of IMO.<<<<Do not
listen to my drivel!!!! *****
looking at the first 'science' screenshot......as far as porting
is involved with this kind of thing.....a bigger hole makes the
frequency Hz value change.
then, looking at my corrected screenshot......those frequencies
are really up there. for example.....300 Hz = 18,000
RPM......not sure quite yet if they will make a difference. (in
my erroneous screenshot, an 118.5 cubic inch would be fine for a
chainsaw motor rpm range). will have to run some numbers, have
not got quite that far yet. yes indeed sir, good questions.....
#Post#: 70528--------------------------------------------------
Re: intake/crankcase stuff
By: 1manband Date: March 23, 2016, 8:41 am
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some links for reference information i am using so far:
1. georgia state university resonance and online calcs.:
HTML http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
2. delivery ratio by K&W:
HTML http://www.vintagesnow.com/SledU_Folder/delivery_ratio-1.pdf
3. delivery ratio by N&S:
HTML http://vintagesnow.com/SledU_Folder/33u5gnr3.pdf
#Post#: 70541--------------------------------------------------
Re: intake/crankcase stuff
By: 1manband Date: March 23, 2016, 2:09 pm
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side note: the intake/crankcase res formula, much like exhaust
formulas, are based on sound waves. through experiments, folks
found that they approximate physical testing of pressure waves.
sidetrack to some pressure things. intake-crankcase tuning is
interrelated to porting. since the size of the hole also affects
the intake/crankcase Hz. this helps show what is ideal.
interesting thing at transfer port just close at higher rpm.
from reference #2 below.
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