Author Topic: intake/crankcase stuff  (Read 306 times)

0 Members and 0 Guests are viewing this topic.

Offline 1manband

  • Nitro Hotsaw
  • *******
  • Posts: 759
  • Karma: 51
Re: intake/crankcase stuff
« Reply #20 on: March 25, 2016, 03:46:12 pm »
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.

hiatus

Offline 1manband

  • Nitro Hotsaw
  • *******
  • Posts: 759
  • Karma: 51
Re: intake/crankcase stuff
« Reply #21 on: March 25, 2016, 05:03:22 pm »
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.
hiatus

Offline 1manband

  • Nitro Hotsaw
  • *******
  • Posts: 759
  • Karma: 51
Re: intake/crankcase stuff
« Reply #22 on: March 25, 2016, 06:38:47 pm »
link to 64 page scavenging/helmholtz paper by engelman.  i mentioned before. long intensive read.  about page 50 or so.

4. engelman http://minds.wisconsin.edu/handle/1793/396?show=full
hiatus

Online 3000 FPS

  • Moderator
  • Nitro Hotsaw
  • *******
  • Posts: 3936
  • Karma: 214
  • Location: Carpenter, Wyoming
Re: intake/crankcase stuff
« Reply #23 on: March 25, 2016, 10:24:21 pm »
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.
PP 505, 475, 445.

Offline 1manband

  • Nitro Hotsaw
  • *******
  • Posts: 759
  • Karma: 51
Re: intake/crankcase stuff
« Reply #24 on: March 26, 2016, 07:16:53 am »
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.

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.
hiatus

Offline 1manband

  • Nitro Hotsaw
  • *******
  • Posts: 759
  • Karma: 51
Re: intake/crankcase stuff
« Reply #25 on: March 26, 2016, 08:05:10 am »
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.

hiatus

Online 3000 FPS

  • Moderator
  • Nitro Hotsaw
  • *******
  • Posts: 3936
  • Karma: 214
  • Location: Carpenter, Wyoming
Re: intake/crankcase stuff
« Reply #26 on: March 26, 2016, 11:05:44 am »
Thanks for the info.
PP 505, 475, 445.

Offline 1manband

  • Nitro Hotsaw
  • *******
  • Posts: 759
  • Karma: 51
Re: intake/crankcase stuff
« Reply #27 on: March 27, 2016, 10:50:02 am »
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.





hiatus

Offline aclarke

  • Nitro Hotsaw
  • *******
  • Posts: 1676
  • Karma: 170
Re: intake/crankcase stuff
« Reply #28 on: March 27, 2016, 10:56:54 am »
Joe,
Are the TA number above based on your modified Blair/Jennings numbers?

Offline 1manband

  • Nitro Hotsaw
  • *******
  • Posts: 759
  • Karma: 51
Re: intake/crankcase stuff
« Reply #29 on: March 27, 2016, 12:29:45 pm »
Joe,
Are the TA number above based on your modified Blair/Jennings numbers?

nope. the numbers from the program posted in other thread.  if i'm understanding the question correctly?
hiatus

 

Related Topics

  Subject / Started by Replies Last post
9 Replies
1432 Views
Last post January 21, 2012, 08:12:30 pm
by tommyhnavix
10 Replies
1296 Views
Last post August 27, 2012, 01:13:55 pm
by CASE5854x4
4 Replies
121 Views
Last post November 10, 2013, 08:08:03 pm
by eatonpaving
7 Replies
207 Views
Last post December 23, 2013, 06:18:37 pm
by SawTroll
2 Replies
288 Views
Last post February 21, 2014, 10:24:29 am
by SDB777
6 Replies
471 Views
Last post May 30, 2014, 08:24:23 pm
by Billyram
28 Replies
1032 Views
Last post August 23, 2014, 07:49:58 pm
by mdavlee .
4 Replies
354 Views
Last post March 18, 2016, 07:01:25 pm
by Philbert
12 Replies
263 Views
Last post September 23, 2015, 06:28:29 am
by jmester
4 Replies
381 Views
Last post February 21, 2016, 03:46:58 pm
by Flip D