CFM to PSI questions

[PsiStar]

IIRC turbochargers reach 10's of 1000 RPM.

well ... yes actually. Although the ones in stock VW are thousands. I went nuts & did this http://forums.nasioc.com/forums/showthread.php?t=1510127 ... I think it spins some ludicrous thing like 15K to 25K. 800 HP does get your mind off computers for a bit.

 

[Eli]

In a word "NO!"

A naturally aspirated engine (aka no boosting of any kind) *often* can handle up to 8 to 10 psi of boost with add on turbo or supercharger. An electric motor would draw many Amps at 12 VDC to be able to provide similar psi.

Hold you hand over the car's exhaust & have a friend push the accelerator to 5000 RPM ... note the pressure. Imagine twice that and that is assuming that you have enough fuel flowing.

Alternatively try this thought experiment, a turbo powered by the engine exhaust spins at several thousand RPM to produce enough pressure at the necessary flow rate ... this is way past even a gas powered leaf blower.

Yes, this should be in the garage ...

That's why I suggested putting the battery powering the blower on a switch. You could then use the energy stored in the battery to run the blower without bogging the engine via the alternator.

I don't understand the point of the "hold your hand over the exhaust" experiment. I don't think exhaust flow would necessarily double, even at double ATM(14PSI), but it might at that point.

 

[Eli]

well ... yes actually. Although the ones in stock VW are thousands. I went nuts & did this http://forums.nasioc.com/forums/showthread.php?t=1510127 ... I think it spins some ludicrous thing like 15K to 25K. 800 HP does get your mind off computers for a bit.

There are no turbochargers that spin less than 10,000RPM.

15k to 25k RPM is low for a turbocharger. Think more like 50k.

 

[Billb2]

254 CFM @ 6k RPMs. Unless I did math wrong.

NO. That will give you zero pressure from the blower. Any airflow OVER your required 254 CFM will be boost.

We looked into this pretty hard for a lemons car. Set up with a leaf blower on a button on the steering wheel as "push-to-pass". Looks like the giant alternator needed would take about as much power to run as the leaf blower would gain. We're going to do two races this year (Nelson Ledges and Autobahn). We may try it at Autobahn depending on how the first race goes. We had the reliability and the lap times to win Nelson Ledges last year, but penalties took us out of the running.

There's a bunch of stuff on YouTube, like this one.
http://www.youtube.com/watch?v=dyR0U_fYtwY

http://www.24hoursoflemons.com/

Oh, and P-Q curve:
http://www.arx-group.com/pq.html

 

[Rubycon]

http://www.youtube.com/watch?v=dyR0U_fYtwY
http://www.24hoursoflemons.com/

Are they just holding the nitrous oxide bottle in front of the leaf blower? Noticed this on the truck run. Wow that's really dangerous. They would be kind of messed up if there was a backfire!

What does NAAAAWWWWZZZ mean? Are they trying to say NOS? Damn boys!

 

[FDF12389]

NO. That will give you zero pressure from the blower. Any airflow OVER your required 254 CFM will be boost.

Thats why I wanted to run two...

 

[Billb2]

Thats why I wanted to run two...

3 Alternators and 2 inverters?

You're not understanding the P-Q curve.
The first "blower" will have no effect ( the engine is already sucking in the 254 CFM by itself).
Adding a second blower is series will have no effect because no matter how many you put together they can't deliver more than 265 CFM. If you put them in parallel you'll get 560 CFM, very little "boost"... 5.5 inches of water = about 0.2 psi.
The hierarchy of fan pressures (at the same CFM) is:
Centrifugal blowers > Squirrel Cages > Axial Fans.

Leaf blowers, that's the way to go.........

 

[Eli]

So it looks like the leaf blower gave 10-15HP? lol.. not bad I guess.. haha

 

[iGas]

I'm not sure what a dynamiter pipe is, but putting 2 fans or pumps in series will double static/head pressure. However, the pressure rapidity drop off as it reach maximum flow rate (maximum flow of 2 fan in series = 1 fan max flow rate).

That said, you will be able to increase flow rate in a device with the same given backflow, but it will not increase much if you are already at maximum outlet flow rate (CFM).

Increasing pressure & flow isn't going to give you the best performance that you can get because most device are design to operate within 1 bar (1 atmosphere, or 14.7 PSI), and it will be very inefficient if you want to work with 1.2 bar or greater. Hence, increase in exhaust size maybe a requirement. Also, air intake baffle might be a good idea as to get laminar flow so that you will have even flow/mixture.

Sorry, I don't know much regarding car, but if flow is similar to burner engines, pumps, blowers, then the above applies.

 

[iGas]

3 Alternators and 2 inverters?

You're not understanding the P-Q curve.
The first "blower" will have no effect ( the engine is already sucking in the 254 CFM by itself).
Adding a second blower is series will have no effect because no matter how many you put together they can't deliver more than 265 CFM. If you put them in parallel you'll get 560 CFM, very little "boost"... 5.5 inches of water = about 0.2 psi.
The hierarchy of fan pressures (at the same CFM) is:
Centrifugal blowers > Squirrel Cages > Axial Fans.

Leaf blowers, that's the way to go.........

2 blowers/pumps in parallel double the flow rate given the same outlet pressure. And, zero static pressure increase.

 

[Rubycon]

2 blowers/pumps in parallel double the flow rate given the same outlet pressure. And, zero static pressure increase.

That's also assuming the increase in flow does not increase pressure.

The units (y scale) on the graph are not labeled. One would presume that given the fact the power input is over one half horsepower that those are in pounds per square inch and not inches of water column! If the latter I don't see where they can label it as extreme pressure! A blower on a pipe organ will do 35 inches (over 1 PSI) at 3500CFM. (of course it's a little bigger! )

 

[Fenixgoon]

someone correct me if i'm wrong, but can't you just use the bernoulli equation and assume 100% pressure loss (ie, full conversion of pressure loss into the velocity of the exit fluid)

P = 0.5*density*(velocity^2)

velocity*area = volumetric flow rate.


not that it's physically correct for what the OP is stating.. but let's assume it is

 

[Billb2]

someone correct me if i'm wrong, but can't you just use the bernoulli equation and assume 100% pressure loss (ie, full conversion of pressure loss into the velocity of the exit fluid)

P = 0.5*density*(velocity^2)

velocity*area = volumetric flow rate.


not that it's physically correct for what the OP is stating.. but let's assume it is

AARRRGGGHHHhhhhh
That's what a P-Q curve does, except it corrects for the inefficiency of the impeller/fan blades. Note that max pressure is at zero flow and max flow is at zero pressure, as Bernoulli would predict.

And there are two places on the page that indicate that the Y axis is inches.

 

[PlasmaBomb]

254 CFM @ 6k RPMs. Unless I did math wrong.

Don't Bother.

The most efficient type of supercharger, flowing 265 cfm and developing a boost of 11.5 psi, takes 14.5kW to drive it.

 

[PsiStar]

.
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We looked into this pretty hard for a lemons car. Set up with a leaf blower on a button on the steering wheel as "push-to-pass". Looks like the giant alternator needed would take about as much power to run as the leaf blower would gain. We're going to do two races this year (Nelson Ledges and Autobahn). We may try it at Autobahn depending on how the first race goes. We had the reliability and the lap times to win Nelson Ledges last year, but penalties took us out of the running.
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Sigh ... guess I haven't been paying any attention to auto sports since I put my car in storage.

Maybe you can figure out a back EMF generator system as a part of braking to provide power for the leaf blower .... just thinking about another place to scavenge power. Not saying its simple:hmm:

 

[Billb2]

.... just thinking about another place to scavenge power. Not saying its simple:hmm:

The "push-to-pass" turbo has fallen by the wayside. The Lemons races are by invitation, so we thought it would be a good "hook". But it's to much work as we're fielding 4 cars this year.
SCCA Spec Racer Ford (two cars, full season)
IMSA Lites (partial season)
Lemons (two or three races)

We're Clueless racing. Look for us on Speed Vision/ESPN (HA!)

 

[Possessed Freak]

You could tow this puppy around.

http://www.govliquidation.com/auction/view?id=2926533&convertTo=USD