Author Topic: port mapping (easy way)  (Read 324 times)

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Offline 1manband

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port mapping (easy way)
« on: October 18, 2015, 07:51:57 pm »
re-read my other thread, just now:  http://chainsawrepair.createaforum.com/ported-saws/port-mapping-old-school/

clear as mud it is.  hope to wash some of the mud off in the next few days.

this is where the story starts:  http://www.bridgestonemotorcycle.com/documents/aspirin_takers6.pdf



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Offline 1manband

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Re: port mapping (easy way)
« Reply #1 on: October 18, 2015, 08:24:25 pm »
the way the graph works, you have to figure out both angle area, and mean port area yourself. 

one figured out, you follow each of those numbers across or up the graph, to see where they meet.

where they meet is the 'time area'.
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Offline 1manband

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Re: port mapping (easy way)
« Reply #2 on: October 18, 2015, 08:53:52 pm »
first thing that i would do is figure out 'angle area'

you need a couple of things before a number can be had.

looking about, most folks here and elsewhere talk in degrees.

seems where the port opens in degrees is talked about more often than port durations.   (opposite is true most everywhere else).

going with that.

looking at a typical exhaust port:

degrees where the port just starts to open, for example is 97 degrees ATDC.  ATDC = after top dead center.  TDC is top dead center, where the piston is physically located at the uppermost point of its travel. (at TDC = 0 degrees).

---------------------------------------------------------------------------------------------------

to find 'durations'.........the amount of angle degrees a port is open can be done a few different ways.

Port Open Durations:

Exhaust Port Opens @ 97 degrees ATDC.  so, 97 x 2 = 194; then 360 degrees - 194 degrees = 166 degrees duration.
Transfer Port Opens @ 121 degrees ATDC. so, 121 x 2 = 242; then 360 - 242 = 118 degrees duration

Blowdown is simply: Degrees Trans first opens - Degree Exhaust first opens = 121 - 97 = 24 degrees duration.

Intake is a little different, because most it seems measure the opening degrees BTDC in saws.  (before top dead center).

Intake Port Opens @ 75 degrees BTDC.  so, 75 x 2 = 150 degrees duration.




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Offline 1manband

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Re: port mapping (easy way)
« Reply #3 on: October 18, 2015, 09:09:07 pm »
you need to find the durations before you can find the 'angle area'.
-------------------------------------------------------------------------------

next up is finding the 'mean angle degrees'.

easy.

you take the degrees where a port just starts to open, and use it like this.

using the exhaust port above as an example.

Exh. Opens Degrees = 97 ATDC

plug it into.....

180 degrees - Exh. Port Opens Degrees = 180 - 97 = 83 degrees

then,

83 divided by 2 = 41.5 degrees

41.5 degrees is called the 'mean angle degrees'

other ports are similarly done.

---------------------
next up is finding 'mean port area'.  have to draw some things to show how.  tomorrow.
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Offline 1manband

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Re: port mapping (easy way)
« Reply #4 on: October 18, 2015, 09:21:08 pm »
in my opinion, the 'mean port angle' carries more weight, than where a port first opens degrees.  not talked about, but hope to show why.
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Offline aclarke

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Re: port mapping (easy way)
« Reply #5 on: October 18, 2015, 10:44:18 pm »
Cool stuff , wish my brain worked like yours does with math!!!  63PS Chain and a few good beers coming your way via UPS in AM

Offline 1manband

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Re: port mapping (easy way)
« Reply #6 on: October 19, 2015, 04:05:59 pm »
Cool stuff , wish my brain worked like yours does with math!!!  63PS Chain and a few good beers coming your way via UPS in AM

this brain is shot.  trying to keep numbers to a bare minimum.

will put together two very small programs that will do all the numbers for yall.

still, some degrees will be needed to be had.  so a wheel will be necessary.

one version, you will need the find connecting rod length.

another version, where connecting rod length is not needed.  this will not be as accurate, but close enough to be in the wheelhouse.
so all that you need is a wheel and calipers.

both will use an extended version of the jennings graph.

beer....ya man.  pesos and beer back at ya.





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Offline 1manband

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Re: port mapping (easy way)
« Reply #7 on: October 19, 2015, 05:49:24 pm »
what mean port area looks like.
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Offline 1manband

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Re: port mapping (easy way)
« Reply #8 on: October 19, 2015, 07:16:03 pm »
/
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Offline 1manband

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Re: port mapping (easy way)
« Reply #9 on: October 19, 2015, 07:17:18 pm »
mark the top of the spigot
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