Chainsaw Repair

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.

more in a bit.

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.

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.....

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.