Quote:
Originally Posted by arcosine
saturn sc1:
14.2-8 = 6.2 psi differential pressure
1905 liter displacement
4 stroke engine
2042 RPM at 65 mph
Pv = pressure * volume/ time
Pv = (6.2 * 4.448/.0254^3) * (1905/1000/4) * (2042/60) * 1.34/1000 = 36 hp
units:
Pv = (psi* N/lbf * m^3/in^3) * (L/m^3/intake strokes per revolution) * rpm/(min/s) = N *m/s
N*m/s /1000*1.34 = hp
6.2 psid
1.905 liter displacment
2042.14153122327 rpm
power, KW 27.2
HP vacuum 36.5
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I'm going to do this in English units since it's what I'm most familiar and comfortable with. I'll carry the units through so we can see what we're dealing with. Remember that power is work per unit time, work is force times distance, so power is force times distance per unit time. This is commonly expressed as 1 HP = 33,000 ft-lbs/minute or 550 ft-lbs/sec.
1905 cc = 114.3 cu. in.
Start with your formula:
Pv = pressure * volume/ time
6.2 psi * 114.3 cu. in./2 (this 2 is based on my previous assertion that you only have one intake stroke per 2 revolutions so you have to divide the displacement by 2) * 2042/60 = 12059 in-lbs/sec.
12059/12 (inches in one foot) = 1004.9 ft-lbs/sec.
1004.9/550 (ft-lbs/sec in 1 HP) = 1.83 HP.
So the "vacuum horsepower" is only 1.83. I think this is measuring (if it's really measuring anything) the pumping loss of actually getting the air into the engine, not the engine output. Remember the pressure in the engine on the power stroke is much higher than 6 psi.
Please point out if I made any mistakes in the equations - I've had a lot of interruptions while I wrote this.