Author Topic: intake/crankcase stuff  (Read 334 times)

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Offline 1manband

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intake/crankcase stuff
« on: March 22, 2016, 04:11:43 pm »
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.
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #1 on: March 22, 2016, 06:38:29 pm »
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.




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Offline 1manband

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Re: intake/crankcase stuff
« Reply #2 on: March 22, 2016, 06:54:56 pm »
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.

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Offline 1manband

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Re: intake/crankcase stuff
« Reply #3 on: March 22, 2016, 07:01:56 pm »
more in a bit.
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #4 on: March 22, 2016, 08:29:07 pm »
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.

 

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Offline 1manband

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Re: intake/crankcase stuff
« Reply #5 on: March 22, 2016, 10:02:51 pm »
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.
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Re: intake/crankcase stuff
« Reply #6 on: March 22, 2016, 10:51:35 pm »
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.   
PP 505, 475, 445.

Offline 1manband

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Re: intake/crankcase stuff
« Reply #7 on: March 23, 2016, 01:05:21 am »
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.

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.....

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Offline 1manband

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Re: intake/crankcase stuff
« Reply #8 on: March 23, 2016, 09:41:30 am »
some links for reference information i am using so far:


1.  georgia state university resonance and online calcs.:  http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

2.  delivery ratio by K&W: http://www.vintagesnow.com/SledU_Folder/delivery_ratio-1.pdf

3.  delivery ratio by N&S: http://vintagesnow.com/SledU_Folder/33u5gnr3.pdf
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #9 on: March 23, 2016, 03:09:18 pm »
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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