psi to cfm
- Thread starter xt falcon
- Start date
A few ground rules.
1. Q is flow in cubic feet
per minute
2. Q=V/A, where V is volume, and A is area.
3. F=P/A, which is psi (pounds [Force] per square inch [Area], or equal to a force)
4. P=density*g*h, where
P=pressure
density = is relative density of fluid (1 for H20, 13.56 for mercury)
g= gravity in 9.81 m/s, or 32.2 ft/sec
h=head in mm of a standing column or inches
5. At 1.5 inches of mercury (hg) gauge pressure, which is 20.3 inches of water, an industry bench mark, the psi would be only 0.734 psi. 9psi is about 249 inches of water, or 18.3 inches of mercury of pressure. Quite a lot of pressure.
6. At sea level, the there is 14.7 psi of absolute pressure, or 29.9 inches of mercury, or 405 inches(!) of water.
So for Q=1460 cfm @ 10000 rpm, you gotta get an area or volume to work it all out. And I have no idea what those figures are, although MarkZE says the rarer, 25 mm longer SC14 runs 1.4 litres per revolution, which is 85 cubic inches, so the SC12 should be about 73 cubic inches or 1.2 litres per rev. Most supercharger or turbo makers supply an abdidaitic chart, which rates the flow verses rpm verses pressure figures.
1460 cfm at 9 psi works out to enough to flow 913 hp, but I doubt this is at 9 psi. I'd say at 9 psi, one supercharger would flow 400 cfm. If you change the delivery pressure to the engine, the flow rate drops.
Boost Ratio = (psi boost+psi air pressure at sea level)/air pressure at sea level
Forcing air through a supercharger gives you a theoretical boost ratio at 9 psi of (9+14.7)/14.7, which is 1.61 times the flow rate of the stock engine, but you loose 10-20% of this because the heat factor of the supercharger.
StrangeRanger would have better math is better than mine, hate to pass the buck, but he could help I think!
What I do know is:
1. a single SC12 @ 9 psi flows 225 hp real easily on a 3.8 Buick. My friends Commodore gets along better than an SV 5000 or 255 Gen III.
CRS got him the Kit in NZ for less than $2000
2. 250 hp is the limit for this blower on its own
3. 280 HP is the limit for the latest single updated SC12 version made in Japan for aftermarket consumption.
With twin superchargers and about 9 pounds, 500 hp should be really easy. On a normally aspirated V8, you need at least 800 cfm at 1.5 inches of Hg at the air intake
1. Q is flow in cubic feet
per minute
2. Q=V/A, where V is volume, and A is area.
3. F=P/A, which is psi (pounds [Force] per square inch [Area], or equal to a force)
4. P=density*g*h, where
P=pressure
density = is relative density of fluid (1 for H20, 13.56 for mercury)
g= gravity in 9.81 m/s, or 32.2 ft/sec
h=head in mm of a standing column or inches
5. At 1.5 inches of mercury (hg) gauge pressure, which is 20.3 inches of water, an industry bench mark, the psi would be only 0.734 psi. 9psi is about 249 inches of water, or 18.3 inches of mercury of pressure. Quite a lot of pressure.
6. At sea level, the there is 14.7 psi of absolute pressure, or 29.9 inches of mercury, or 405 inches(!) of water.
So for Q=1460 cfm @ 10000 rpm, you gotta get an area or volume to work it all out. And I have no idea what those figures are, although MarkZE says the rarer, 25 mm longer SC14 runs 1.4 litres per revolution, which is 85 cubic inches, so the SC12 should be about 73 cubic inches or 1.2 litres per rev. Most supercharger or turbo makers supply an abdidaitic chart, which rates the flow verses rpm verses pressure figures.
1460 cfm at 9 psi works out to enough to flow 913 hp, but I doubt this is at 9 psi. I'd say at 9 psi, one supercharger would flow 400 cfm. If you change the delivery pressure to the engine, the flow rate drops.
Boost Ratio = (psi boost+psi air pressure at sea level)/air pressure at sea level
Forcing air through a supercharger gives you a theoretical boost ratio at 9 psi of (9+14.7)/14.7, which is 1.61 times the flow rate of the stock engine, but you loose 10-20% of this because the heat factor of the supercharger.
StrangeRanger would have better math is better than mine, hate to pass the buck, but he could help I think!
What I do know is:
1. a single SC12 @ 9 psi flows 225 hp real easily on a 3.8 Buick. My friends Commodore gets along better than an SV 5000 or 255 Gen III.
CRS got him the Kit in NZ for less than $2000
2. 250 hp is the limit for this blower on its own
3. 280 HP is the limit for the latest single updated SC12 version made in Japan for aftermarket consumption.
With twin superchargers and about 9 pounds, 500 hp should be really easy. On a normally aspirated V8, you need at least 800 cfm at 1.5 inches of Hg at the air intake
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