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Author Topic: Air mass & boost to approx RPM  (Read 16033 times)
userpike
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« Reply #15 on: August 12, 2013, 01:47:39 PM »

if an engine has a displacement of 1.8 liters, that is for all the cylinders combined. if you do the math using bore and stroke you'll see the whole number of displacement can be divided by the number of cylinders. So in a 1.8L 4 cylinder engine, the displacement for each cylinder would roughly be a quarter of the total engine displacement. in a 6cyl, 1/6 of the total displacement equals individual cylinder displacement. same with a 8cyl and so on.

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masterj
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« Reply #16 on: August 12, 2013, 02:10:02 PM »

if an engine has a displacement of 1.8 liters, that is for all the cylinders combined. if you do the math using bore and stroke you'll see the whole number of displacement can be divided by the number of cylinders. So in a 1.8L 4 cylinder engine, the displacement for each cylinder would roughly be a quarter of the total engine displacement. in a 6cyl, 1/6 of the total displacement equals individual cylinder displacement. same with a 8cyl and so on.



I've already divided that into 4...
DISP = 1780 / 4 = 445 cm^3 = 0.000445 m^3
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nyet
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« Reply #17 on: August 12, 2013, 03:47:14 PM »

VE 95 is 95%, not 95...
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masterj
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« Reply #18 on: August 13, 2013, 11:54:36 AM »

VE 95 is 95%, not 95...

Oh, stupid me! So I have to use 0.95 Smiley Now it makes sense!

EDIT:
Still get weird numbers...
0.020.040.060.080.10.120.140.160.18
95189284378473568662757852

Using: VOL * 2 / 0.95 / 0.000445
« Last Edit: August 13, 2013, 12:01:54 PM by masterj » Logged

nyet
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« Reply #19 on: August 13, 2013, 03:07:42 PM »

Please include units and use dimensional analysis to make sure you got the unit conversion right.

I can't make head or tail of what you are trying to do.
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masterj
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« Reply #20 on: August 14, 2013, 12:55:52 AM »

Ok, so let's try this again...

VOL = RPM / 2 * VE * DISP
vvvvvvvvvvvvvvvvvvvvvvvvvv
RPM = VOL * 2 / VE / DISP

Where:
VOL = volume per time (from k.m.)
RPM
VE = volumetric efficiency (I'll be using 95% == 0.95)
DISP = displacement (1780 cm^3 / 4 = 445 cm^3 = 0.000445 m^3)

After this formula becomes:
RPM = VOL * 2 / 0.95 / 0.000445

Now, I try to use VOL from k.m. => 0.02; 0.04; 0.06; 0.08; 0.1... and result is weird
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nyet
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« Reply #21 on: August 14, 2013, 08:35:04 AM »

rpm is per min

what are your target units for volume?

what is "VOL from k.m"
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cerips
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« Reply #22 on: August 14, 2013, 09:57:54 AM »

Your air flow is m3/s and rpm is revolutions per minute, you need a factor of 60 to convert between the two.
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nyet
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« Reply #23 on: August 14, 2013, 11:46:56 AM »

This is exactly what I mean by dimensional analysis.

Try all of your calculations with only conversion constants

rpm * minutes * grams = grams

rpm * seconds * (60 seconds/minute) = 60 * grams

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Do not PM me technical questions! Please, ask all questions on the forums! Doing so will ensure the next person with the same issue gets the opportunity to learn from your ex
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