CFM to PSI questions

[FDF12389]

I'm not sure if this should have been posted in the garage or highly technical but here it is.

Approximately how much PSI could two of these fans in conjunction push throw a 3 in dynamiter pipe?

http://www.kooltronic.com/bb-kbr125.php (Or a similar radial fan)

This is just a curiosity of mine in regards to making a electric induction turbo, I have figured out how to mount a second alternator, and batteries aren't hard to place, now I just need to know if I can generate a decent amount of pressure.

 

[Howard]

Good luck getting enough power into it.

 

[Red Squirrel]

I could be wrong but I think psi and cfm are completly different measurements. PSI is pressure and CFM is airflow, and while they are sorta related, different 100CFM fans can be different PSI based on blade design etc...

Ex: I can take a super high CFM fan and not be able to blow up a balloon but with a lower CFM but more powerful blower I may be able to.

I could be wrong though.

 

[shiner]

What does the sidewall say?

 

[Jeff7]

I could be wrong but I think psi and cfm are completly different measurements. PSI is pressure and CFM is airflow, and while they are sorta related, different 100CFM fans can be different PSI based on blade design etc...

Ex: I can take a super high CFM fan and not be able to blow up a balloon but with a lower CFM but more powerful blower I may be able to.

I could be wrong though.

Indeed.
One measures volume per unit time.
The other measures pressure per area.

You might have better luck with the graph at the bottom of the page, converting pressure in inches of water to psi.

 

[Rubycon]

C/O is 7.5 psig. That's called the cutoff pressure - no airflow but a gauge would measure 7.5 psig. If you're looking to increase charge pressure of an engine this is the wrong approach. You need a screw compressor which is positive displacement.

 

[Eli]

CFM is a measure of flow, PSI is, well, a measure of pressure. You can't convert the two, or figure either based on one. I'm sure there's math to answer your question based on the specs of the blower, but I don't know it.

I must ask though, what the hell are you doing? lol

That blower is 110VAC. Please tell me you aren't going to add an alternator, battery and inverter to your car to power a blower on your intake.. LOL.

It would work, but it will make baby efficiency jesus cry. There is a reason traditional turbos use exhaust for power; it's essentially free energy.

If you're really going to do this, I think adding another alternator is complicating matters. You should have the battery powering the blower on a switch to disconnect it from the alternator. That way you can power the blower and feel the full effects of the boost. Then you can turn the switch on, and cruise for a while.. letting the battery recharge.. waiting for the next red light? lol

 

[Rubycon]

If you're really going to do this, I think adding another alternator is complicating matters. You should have the battery powering the blower on a switch to disconnect it from the alternator. That way you can power the blower and feel the full effects of the boost. Then you can turn the switch on, and cruise for a while.. letting the battery recharge.. waiting for the next red light? lol

Wouldn't it make more sense to use a blower instead of a second alternator?

I have a major beef with this scenario. The problems are in bulk proportions!

Didn't someone on this forum try using a leaf blower to do this?

 

[Eli]

Indeed.
One measures volume per unit time.
The other measures pressure per area.

You might have better luck with the graph at the bottom of the page, converting pressure in inches of water to psi.

LOL! I didn't even see the graph.

/facepalm

OP, just out of curiosity.. what have you figured your CFM requirements to be? lol

 

[Red Squirrel]

You could also use arrays of 120mm fans like I was planning to do for my rack (which I did not or will not do )

(j/k. this would not have much PSI, just really high but wimpy CFM)

 

[Eli]

Wouldn't it make more sense to use a blower instead of a second alternator?

I have a major beef with this scenario. The problems are in bulk proportions!

Didn't someone on this forum try using a leaf blower to do this?

A blower as in a super or turbocharger? Yes, of course it would..

This has fail written all over it.. It has the potential to give some boost.. even 2PSI over ATM would be noticeable.. but you'll need the right equipment. Realize, though, that it is very likely this type of setup would actually hinder performance.

Your blower would have to be able to provide boost at all engine RPMs. If you haven't figured it out yet, the CFM requirements of your engine vary widely between idle and redline.

 

[Rubycon]

LOL why use box fans?

You want a squirrel cage blower! (do they come in red? )

Build a plenum or use an attic space, etc. The discharge can pressurize it directly OR you can fit the discharge with an adapter cutting it down to 12" and run some flex to a gable vent or whatever.

Have a louvered door at the ceiling of your server area. The doors to the living space could have louver vents closer to the floor to pick up the coolest air and you could attach channels to them and slide a 20x25x1 common "home furnace" filter in there to provide some basic filtration.

You could also use arrays of 120mm fans like I was planning to do for my rack (which I did not or will not do )



(j/k. this would not have much PSI, just really high but wimpy CFM)

Yes blower as in screw compressor - the thing that has a big ass belt on it that race drivers use making a raucous noise and providing up to 40 psi of boost!

Those fans use 430W at 120VAC. The alternator is going to be drawing down pretty heavily on the engine when it's engaged. He'll need a motor speed controller as well since you just cannot have the blower going wide open all the time. It's possible to use an electric blower if properly engineered. It sounds like fun (well the control part) project. Like to use on a Ferris wheel to add a turbo boost mode to make it go 200% faster. I don't drive so it wouldn't be of use to me.

A blower as in a super or turbocharger? Yes, of course it would..

This has fail written all over it.. It has the potential to give some boost.. even 2PSI over ATM would be noticeable.. but you'll need the right equipment. Realize, though, that it is very likely this type of setup would actually hinder performance.

Your blower would have to be able to provide boost at all engine RPMs. If you haven't figured it out yet, the CFM requirements of your engine vary widely between idle and redline.

 

[FDF12389]

LOL! I didn't even see the graph.

/facepalm

OP, just out of curiosity.. what have you figured your CFM requirements to be? lol

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

 

[FDF12389]

I would have to have the fans moving enough to not restrict air at idle, then I could have them engage all the way either when the throttle is all the way open, or when I hit fifth gear, its all just curiosity right now.

 

[Eli]

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

So you have around a 2.8L engine?

 

[Rubycon]

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

It's a two pole induction motor. At 60Hz it will run at its spec'd speed of 3450RPM. This is using the typical ~5% slip rating at FLA.

What's not spec'd is if the motor load increases under pressure or decreases.

Take a vacuum cleaner for example. If you put your hand over the hose you will hear the motor increase in pitch. This is because the torque requirement decreases under load. Some blowers are the opposite and the motor will actually slow down if the output is blocked. A vacuum cleaner uses a universal motor which allows its speed to vary dramatically under different conditions whereas an ac induction motor is regulated (within reason) hence the term synchronous motor.

In any case you're not going to want to use a blower like that on a car. Unless you're interested in a street sweeper.

EDIT: NVM I see you're discussing engine RPM not RPM of the (blower) motor.

This should probably be moved over to the garage, eh?

 

[FDF12389]

It's a two pole induction motor. At 60Hz it will run at its spec'd speed of 3450RPM. This is using the typical ~5% slip rating at FLA.

What's not spec'd is if the motor load increases under pressure or decreases.

Take a vacuum cleaner for example. If you put your hand over the hose you will hear the motor increase in pitch. This is because the torque requirement decreases under load. Some blowers are the opposite and the motor will actually slow down if the output is blocked. A vacuum cleaner uses a universal motor which allows its speed to vary dramatically under different conditions whereas an ac induction motor is regulated (within reason) hence the term synchronous motor.

In any case you're not going to want to use a blower like that on a car. Unless you're interested in a street sweeper.

EDIT: NVM I see you're discussing engine RPM not RPM of the (blower) motor.

This should probably be moved over to the garage, eh?

Is there any type of electric motor that could be used?

 

[Red Squirrel]

LOL why use box fans?

You want a squirrel cage blower! (do they come in red? )

Build a plenum or use an attic space, etc. The discharge can pressurize it directly OR you can fit the discharge with an adapter cutting it down to 12" and run some flex to a gable vent or whatever.

Have a louvered door at the ceiling of your server area. The doors to the living space could have louver vents closer to the floor to pick up the coolest air and you could attach channels to them and slide a 20x25x1 common "home furnace" filter in there to provide some basic filtration.

Haha yeah I got a few various plans for a cool setup involving a furnace blower, most likely. That pic was a very early design which I pretty much scrapped. I will probably have a big damper so I can either shoot the hot air into my return vent (furnace blower will pretty much do the air flow work) or shoot it outside (will require a separate blower). Probably just use a dryer vent kit type deal for that. Don't want to shoot out too much air since I have to replace that air and if it's super hot out, then it's not really practical to be throwing hot air out only to get more hot air in. At that point an AC may be more efficient.

 

[Rubycon]

Is there any type of electric motor that could be used?

Well the problem is in a car you have 12V available. You can step this up with decent efficiency however the power (W) is still going to be relatively limited compared to driving a pump directly off the engine crank. At the very least you would need a variable speed motor and driver whose input would be based on manifold pressure. I'm sure this would have to be tied into the engine ECU as well as modifications to timing would be necessary to prevent detonation due to the apparent increase in geometric compression ratio. Increase in fuel octane would be required too.

 

[Eli]

Well the problem is in a car you have 12V available. You can step this up with decent efficiency however the power (W) is still going to be relatively limited compared to driving a pump directly off the engine crank. At the very least you would need a variable speed motor and driver whose input would be based on manifold pressure. I'm sure this would have to be tied into the engine ECU as well as modifications to timing would be necessary to prevent detonation due to the apparent increase in geometric compression ratio. Increase in fuel octane would be required too.

This.

Like I said, this has fail written all over it, unless you are ready to implement these controls.

Find the biggest 12VDC blower motor that you can find, and go from there. After that, you will need a vacuum sensor tied into a PWM controller, which probably wouldn't be that hard overall. If your engine is one that can take small amounts of boost without extensive modification, you might have some fun.. lol

 

[Rubycon]

This.

Like I said, this has fail written all over it, unless you are ready to implement these controls.

Find the biggest 12VDC blower motor that you can find, and go from there. After that, you will need a vacuum sensor tied into a PWM controller, which probably wouldn't be that hard overall. If your engine is one that can take small amounts of boost without extensive modification, you might have some fun.. lol

One good with links could possibly get the throttle plate of a small two stroke leaf blower and their engine throttle close in tune so when the accelerator pedal is pushed down the blower is goosed.

It would be funny to try. Give David up in Canada a ring I bet he's done something similar! http://www.youtube.com/davidsfarm

 

[FDF12389]

Well the problem is in a car you have 12V available. You can step this up with decent efficiency however the power (W) is still going to be relatively limited compared to driving a pump directly off the engine crank. At the very least you would need a variable speed motor and driver whose input would be based on manifold pressure. I'm sure this would have to be tied into the engine ECU as well as modifications to timing would be necessary to prevent detonation due to the apparent increase in geometric compression ratio. Increase in fuel octane would be required too.

Well with the addition of a second alternator I could run two batteries like these for 24V. https://www.1320engineering.net/mit....html?osCsid=de770bff4ef2fd42a24157d7b4dce463


I already have a programmable ECU, I'm just curious to see if this is feasible, mainly for the unique factor. Obviously i could just turbo it, but that's boring I guess.

 

[PsiStar]

Is there any type of electric motor that could be used?

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 ...

 

[Rubycon]

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 ...

IIRC turbochargers reach 10's of 1000 RPM.

 

[Eli]

IIRC turbochargers reach 10's of 1000 RPM.

Beat me to it.

Indeed, turbochargers spin at tens of thousands of RPM, even reaching 100,000 in some cases.