mx5cartalk.com

Those are a scam. They just obstruct the intake with a shitty tiny little fan you'd find normally on a computer.

Think about it like this.....

Let us suppose that your engine is a four stroke 1600cc, with an efficiency of 80%. That means that every revolution requires 640cc of air.

So at idle (900rpm) your engine needs 576,000 cc of air a minute. One cubic decimetre (commonly called a litre) is 1000cc. So that is 576 milk cartons a minute at idle.

One cubic foot is 28.32 cubic decimetres. Again each rpm needs 0.0226cf.

So to boost the engine at idle you would need an electric fan able to pass 20cfm.

To boost it at 3000rpm you need 67.8cfm, 6000rpm needs 135.6cfm, redline needs as near to 170cfm as $h%t is to swearing.

Now to get an electric fan that can pass that amount of air is fairly hard, almost impossible for a 12vDC system. And the additional load on the alternator will be noticeable. Not to mention the weight of the fan motor.

Finally, this is all at ambient atmospheric pressure. If you want to actually produce boost pressure, you need more GRUNT.

Turbo and superchargers are not Fans they're PUMPs

Pumps Produce Pressure, Fans wont.

So even if a fan flows 200cfm it won't boost.

and as the above posts say, the ebay ones are Fans

Sure they work ! I've got a few cheapies here, just send me a crisp $50 note.....

Rotary wrote:Turbo and superchargers are not Fans they're PUMPs

Pumps Produce Pressure, Fans wont.

So even if a fan flows 200cfm it won't boost.

and as the above posts say, the ebay ones are Fans

Not exactly. You're talking about positive vs non-positive displacement pumps. A turbo is non-positive, therefore a compressor. If you blocked the outlet of the system, the system will still work, al-be-it at a positive presure on one side, and negative on the other. A true pump is positive displacement, such as a air or hydraulic compressor where if you block the outlet, the pump will stop dead. The same goes for centrifugal supercharger, it's just a compressor.

http://64.78.42.182/sweethaven/MechTech ... chMod=0301

A root type supercharger is positive displacement, so it is a true pump for the purpose of this argument.

I know that people will give me flack for this, but when I bought the Italia it had one of these things fitted and for a 1600 the thing flew!!

Probably unrelated but still interesting that it went as well as it did.

Peter

Any extra speed wouldn't have been creditable to one of these pieces of junk.

sabretooth wrote:Any extra speed wouldn't have been creditable to one of these pieces of junk.

Has anyone seen the clip of the guys who strapped a leaf blower to their NA car and ran it on a dyno? That actually did work. I'm unable to access Youtube at work here but it wouldn't be hard to find.

Now, a leaf blower is different to a small fan, but the principle is there. Whether or not the power required to run a blower is recouped by the extra power produced is another thing to consider.

I did some research and some do 25000rpms and of course have \"Dyno\" sheets to prove their point!!!!

It would be interesting to get a group to fund a purchase and then do a before and after dyno run.

The English ones go for around 105 pounds.

This is not suggesting they work but an a definate answer would good.

Peter

Just read Ired5's post---don't think I will bother getting a group together!!!!!!!!!!!!!!!!!!!!!!!!!!

The Stihl BG55 Leaf BLOWER from http://www.buywright.co.nz/vacuums.html

710m3/hour = 25,073.4134 ft3/hr, or 417CFM

The scenario adamjp discussed above requires 170CFM, therefore I imagine the above blower would provide 'some' level of boost.

pcmx5 wrote:I did some research and some do 25000rpms and of course have "Dyno" sheets to prove their point!!!!

It would be interesting to get a group to fund a purchase and then do a before and after dyno run.

The English ones go for around 105 pounds.

This is not suggesting they work but an a definate answer would good.

Peter

Just read Ired5's post---don't think I will bother getting a group together!!!!!!!!!!!!!!!!!!!!!!!!!!

25000RPM from one of those fans is laughable. One of those fans would NOT last long in that application. The bearings will seize or start squeeling in short order. Most PC fans carry a sleeve bearing and are just not rated for that sort of work.

I'm sure I can pull a dyno sheet out of my bum to show anything I wanted, too. Instead, give me the 105GBP and I'll duct-tape a couple of fans to someone's car intake. Just don't ask me to do it to mine, because I expect that the fans would fall apart and get sucked into the cylinders before they actually provide any benefit to the engine.

Brad wrote:The Stihl BG55 Leaf BLOWER from http://www.buywright.co.nz/vacuums.html

710m3/hour = 25,073.4134 ft3/hr, or 417CFM

The scenario adamjp discussed above requires 170CFM, therefore I imagine the above blower would provide 'some' level of boost.

The leaf blower's a better option, but the extension cord limits your range a bit.

Cheers,
Alf

Brad wrote:

Rotary wrote:Turbo and superchargers are not Fans they're PUMPs

Pumps Produce Pressure, Fans wont.

So even if a fan flows 200cfm it won't boost.

and as the above posts say, the ebay ones are Fans

Not exactly. You're talking about positive vs non-positive displacement pumps. A turbo is non-positive, therefore a compressor. If you blocked the outlet of the system, the system will still work, al-be-it at a positive presure on one side, and negative on the other. A true pump is positive displacement, such as a air or hydraulic compressor where if you block the outlet, the pump will stop dead. The same goes for centrifugal supercharger, it's just a compressor.

http://64.78.42.182/sweethaven/MechTech ... chMod=0301

A root type supercharger is positive displacement, so it is a true pump for the purpose of this argument.

Your spot on technicaly, but its not what i was trying to point out.

My point was one will boost, while the other will not (tried to avoid getting technical for those not into it, and to make it easier too see i made reference to pumps as most pumps people can relate to produce pressure)

So here's the technical

Why will 1 boost while the other will not?

Quite simply it has nothing to do with CFM and everthing to do with the Energy(power) required to compress air.
All that the CFM tells us is the amount of air that will require Compressing

a $40 King of PC fans will flow 134CFM freestanding
http://www.antec.com/pdf/flyers/BIgBoy_sellsheet.pdf

But this fan is a whole 3.4Watts powerful, not Kw, Watts!, you can stop it with your finger.
As soon as it starts trying to compress the fan will slow to a level where the Flow(CFM) can no longer keep up and therefore won't boost

Now there are formulas to work out the energy required to compress an ideal gas and total volume required etc. etc.
But all are unecessarily complicated as we dont need an exact figure to see why these fans will not work

The figures can be easily seen by looking at supercharger Compressor maps and power required to drive the compressor

Roughly between 10 to 20kw's of power needed depending on CFM and boost requirements,

This Means you will need an electric motor 10-20kw in power to drive an efficient compressor(much more efficient than any leaf blower)

Thats 10,000 to 20,000watts, watt was the BigBoy CPU fan again? 3.4watts

No leaf blowers electric or petrol motor is that powerful either

So by virtue of being very slightly powerful a leaf blower may give some boost, most likely 1-2psi up to 1500rpm and 0.5psi at 2000 rpm, but thats it, because as the revs go up so does the amount of air requiring compressing, which in turn means the Power required to compress all that extra air becomes huge (10-20kw is needed not 0.7kw of the leaf blower)


Long but that simple


Sidenote:
A Leaf Blower is not designed to be a compressor, its designed to flow as much air as possible with no resistance (much like the PC Fan) so when it encounters resistance, it will also suffer a massive drop in rated CFM, becoming very inneficient, spinning hard but not producing flow or boost, just lots of heat

The Ebay S/C fans are about 1.5 watts in power

Thanks Rotary, now it all makes sense