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

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Offline 1manband

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Re: intake/crankcase stuff
« Reply #30 on: March 27, 2016, 12:38:25 pm »
at this point, reasonably confident that the crankcase resonant frequency is based on using the rpm of peak hp.

i cannot however, find any sources to confirm or deny the statement above.

the errors or differences between the porting area vs. the crankcase res area i found were between 560 rpm to 900 rpm off.

i do not think this is too bad, because both of these are 'design' type programs meant to get you in the wheelhouse.

happy Easter everyone.
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #31 on: March 27, 2016, 12:42:08 pm »
.....that's as close as you will ever get to seeing me do a porting thread.   hahaha.  how to use the program, don't have issue w/that.
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #32 on: March 27, 2016, 12:53:55 pm »
what i used to quickly hitt the areas, may be unrealistic....... about 81 or so IO.  and for the other about 1.25 W and 79?  did not write it down.

could go back and record the numbers if need be?
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #33 on: April 02, 2016, 10:20:06 am »
...back to intake tuning.

once the case resonance Hz is found, the next thing that can be looked into is Pulse Tuning.

as per the delivery ratio paper by Nagao & Shimamoto....page 7.....(link is up thread somewhere).

idea is to to use differing lengths and x-sectional areas of the of the intake tract to get " 3/4 of the period of pressure fluctuation coincident with the port opening period."

best pulse values are between 0.7 and 0.8, which in turn give the maximum delivery ratio.

goes like this:

(more to follow).
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #34 on: April 02, 2016, 11:14:32 am »
stock jonsereds 52 intake pulse tuning across the rpm range+

will put some notes on the graph later.

0.7 to 0.8 is sweet spot, about 9500 to 11000 rpm.
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #35 on: April 02, 2016, 03:13:42 pm »
same stock motor w/notes

case resonance frequency = 297 Hz @ 8913 rpm
approx. max tq rpm = 5500
actual max. HP rpm = 8300
maximum motor rpm = 11400
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #36 on: April 03, 2016, 06:03:26 am »
now to do the same thing, raising the power band up approximately 2000 rpm.  don't know yet how it will match with the case res. and pulses.

will spend a bit more time on picking a realistic port x-sectional area.
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #37 on: April 03, 2016, 11:51:13 am »
took some time to get some realistic numbers.  thing is, there is not enough material there to widen the intake manifold out enough.  the manifold is made of what looks like bakelite, has 6 panhead bolts holding it onto the cylinder, along with two carb bolts.  the pulse port on the manifold feeds the carb, and is located very close to the perimeter of the stock hole.

so, the stock manifold hole can only be brought out to 0.820" diameter.  this yields an maximum x-sectional area of 0.528 in2.  that is the maximum area value, i will be using for my port mouth opening at the cylinder.

what all this means, is by using the porting program set to a max area value of 0.528 in2, looks like the most i can raise the power band is only 430 rpm while keeping the rest of the ports all balanced.

the following screenshot shows what the rpm ranges/case res rpm/pulse tuning sweet spots morphed into using the design programs formulas.
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Re: intake/crankcase stuff
« Reply #38 on: April 03, 2016, 02:31:45 pm »
So if you can get the saw to turn around 10K in the cut you would be at resonance?
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #39 on: April 03, 2016, 06:23:43 pm »
So if you can get the saw to turn around 10K in the cut you would be at resonance?

believe that is the case.

when i plugged in the value for the largest intake port area i could fit in the formula, it raised the case resonance frequency from
the stock 297 Hz @ 8913 rpm up to 329 Hz @  9871 rpm.

the rpms where the best pressure pulses also moved up in rpm range from the stock values as well, by about a 1000 rpm.

both instances now have breaks between them, in the stock configuration this was not the case.

looks like the resonance and the porting are not a 1 for 1 in rpm thing.  interesting just how much a
area change from 0.428 in2 to 0.528 in2; and 5 degrees of duration actually makes.

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