Author Topic: intake/crankcase stuff  (Read 328 times)

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Offline 1manband

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Re: intake/crankcase stuff
« Reply #40 on: April 05, 2016, 07:18:50 pm »
eric gorr writes how this stuff can be useful. (will post the link up when i find it again).

i am not the best explainer as y'all can already see, because i look at these thing with graphs and such.

so, by varying the length and area one could raise or lower the intake tuning just about anywhere in the rpm range and nudge power band hit around a bit.

by using a spacer, lowering the tune for more of a torque hit is possible.

1/2 inch spacer, between the carb and intake port spigot, lowers the rpm hit by 700 rpm.
1" spacer....................................................................lowers the hit by 1200 rpm.

going the other way, shaving a 1/2" off, yields about an 800 rpm raise in the intake tune.

imo, a tach or the way chrispa suggests would be necessary to get rpm readings to realize the intake tuning benefit. or, if the tach won't read on the new fangled motors.  how anyone ports without a tach is beyond this discussion. 

as far as the case volume thing goes, for my motor, they picked a very good volume already.  don't know about others. porting raises the rpm, with not much to worry about as far as intake tuning, at least from the one example i am basing this on.

for the race crowd:  looked at what only decreasing the case volume, would do on my little motor.
for every in3 reduced case volume, about +700 rpm intake tuning went up.  not that much.
however, when port area was increased by about 30%, with 2 in3 less volume, rpm tune went up about 4000 rpm, max rpm up to 17.5k

eric gorr and frits overmars/jan thiel do have some interesting reads.




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Re: intake/crankcase stuff
« Reply #41 on: April 06, 2016, 09:20:31 am »
Makes sense to me.     The larger the volume the lower the frequency and the smaller the volume the higher the frequency.   Got it.
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #42 on: April 07, 2016, 05:29:50 am »
most all of the references on this topic explain the process, the amount of measured benefit of all this to me remains unclear.
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #43 on: April 09, 2016, 06:36:44 am »
...found a couple of references that mentioned gains.  was going to put this all behind me.

eric gorr writes that..'effect will be unmistakable, engine will pull very strongly when it comes on the (sic. intake) pipe.'

engleman paper......'effect over very broad rpm range'

gorr goes on to write that mcculloch gave him some insight on how they test for this.  they affix a very short exhaust stub, to take the exhaust effects out.  they then cut and try differing lengths of intake pipes, to find which work the best.

this is somewhat contradictory to what nagao & shimamoto write......'finding an intake tuning alone (without considering exhaust) may or may not be optimum when an exhaust is affixed.'

another way to test intake tuning was in the engleman paper.  the lauson company, spun up a motor with a compression gauge attached to it.  the tuned intake gave higher compression numbers accross the board. 

would be just about impossible to spin up a saw motor to its power range?.....to use this method.

the lauson test showed about 10 psi gain minimum depending on length and area of inlet pipe tested.

.........
at this point, i am just going to get the formula more accurate by putting in a temperature and open end correction, and that is it, for less cut and try hopefully.

the motor manufacturer's most likely already incorporate intake runner tuning into their designs these days anyway for the rpms they spec out.
wondered just what would happen when the rpm range was changed with porting, etc.

have never read of a thread where someone tried working numbers out for these small high rev motors, so i thought would give it a go.  is what it is.

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Re: intake/crankcase stuff
« Reply #44 on: April 10, 2016, 02:13:36 pm »
So then can we measure the RPM  of an engine and then try different lengths of intake tube and by the using the RPM's can we then determine which one is the most beneficial for the saw.    In other words is the RPM's going to be at it's highest level when the intake length is at it's most beneficial.
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #45 on: April 11, 2016, 06:08:18 pm »
i believe so.

the way the test is described for a motorcycle:  equipped with both a stub exhaust and a tachometer, pointed up a hill or long road, in order to load the engine heavily, to see where the intake pipe has it's effect on power, being most prominent at a certain rpm or speed.

maybe it would be similar idea?  Check ct stock length, note rpm.  then check with altered length, to see what rpm it hitting hardest at.

I do not know, for certain, have never tried this.

the calculations would give an idea of what to expect before testing for rpms, using different combinations of length, area and volume. And what combos to try to move rpms around where you want to.
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #46 on: April 13, 2016, 06:17:20 am »
found a few more bits of information.

the carb area has to be close to the inake runner x-sectional area or the intake ramming effect is diminished.  a ratio of 0.7 or greater is the goal.

stock sizes: carb venturi area = 0.31 in2;  intake x-sect area = 0.43 in2......so 0.31 divided by 0.43 = 0.73 works.

same carb with larger port sizing:  carb = 0.31, intake area = 0.53......0.31/0.53 = 0.59 .......intake ramming diminished.


also found some saw motor temperatures from blair page 391 figure 5.25 graph.

crankcase internal temp range from 140F to 248F.  average about 212F.  (so, most vaporization is happening in the cylinder, not the c.case).

intake runner internal from 68F to 122F. average about 104F.


have enough info to include corrections into the formula now.
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #47 on: April 14, 2016, 07:49:00 am »
so i worked out the formulas with some different temperatures.

quite a bit of swing when the temperature goes up.

do not know which temp would best represent or mimic real world conditions.

all these formulas use the speed of sound.  but speed of sound goes up as temperature goes up.  this changes things quite a bit.

nagao & shimamoto/engleman did not include a temperature correction.  believe it is important to represent intake tuning as they do.
they used a speed of sound value at 68F (20C).  so will include that.

will also include and use the average runner temp in a separate calc.
lastly will use what blair settled on for thermo calcs and show this.  212F (100C).

somewhere, within those temp ranges is what i believe is happening?

maybe it is like these different exhaust programs, some closer to the mark than others.

will post up what it looks like.
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #48 on: April 14, 2016, 07:50:48 am »
......then was thinking of making up some wood spacer blocks.
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Re: intake/crankcase stuff
« Reply #49 on: April 14, 2016, 12:31:42 pm »
......then was thinking of making up some wood spacer blocks.

Or some small aluminum ones.    A man with your talent it should be a piece of cake.
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