Shop-Vac Turbo, WOULD IT WORK?

[drivebyrachko]

So a friend of mine bought a 1987 BMW 325e (the 2.7L 121hp kind) for very cheap and only plans on using it for a month or two, so its basically expendable. We've always wanted to do something ridiculous called the "Shop-Vac Turbo," which, for those of you who don't know, is getting an industrial sized vacuum cleaner, setting it to "blow" out of the inlet hose, and hook that up to the intake (the shopvac could fit anywhere in the car, its too big to be under the hood but we have hoses ) for some real ghetto boost. So for those of you more mechanically inclined than I, what issues would you foresee with such a project? Is it really even feasible? Sounds like a lot of fun, but as a SAAB owner ('97 900 SE Turbo Stage II) I do find boost abuse amusing, and as a former BMW ('99 323i) owner, sort of troubling, but what the hell, the BMW wasn't even $900, and has plenty of mechanical issues already, such as it likes to stall at traffic lights.

Anyways, say what you wish, any advice or comments are appreciated!

[shorod]

Oh, not again! This topic has been addressed before on this forum. Please use the 'Search this forum' feature and read the educational and informative posts on the subject.

-Rod

[drivebyrachko]

Really? I'm not finding anything, too many ways to phrase it and if I say "turbo" or "supercharger" I get a post from anyone with a turboed vehicle

[curtis73]

Do a general internet search for things like "leaf blower turbo" or "shop vac supercharger" and you'll get tons of results.

It won't work. Shop vacs make vacuum and flow, not pressure. That "pressure" you feel on your hand when it blows on it is simply flow. As you put your hand closer and closer to the nozzle, there is less and less force on your hand, until you finally cap the nozzle and almost all pressure stops since you have halted the flow.

Don't confuse force with pressure. Force from flow won't help. You need to actually compress the air. Tests have been done a few thousand times. Even the biggest leaf blower or shop vac only makes about 1/2 psi... which does help power on a theoretical level. There was a youtube video showing a civic on a leaf blower and it gained like 3 hp.

But, there is no free lunch. If you want to make that power with a shop vac, you have to have a 120v generator that is capable of about 15 amps. That is the equivalent of adding an 1800-watt amplifier to your stereo. It takes HP to spin a generator... more than you get back with the shop vac. First law of thermodynamics can't be violated. You can't get back more than you use.

[drivebyrachko]

Ok, leaf blower may work, well suppose I got a nozzle attachment that got steadily smaller and smaller in diameter to create pressure, then introduce it to the engine at the end? But I'm used to 20psi boost on my Stage 2 SAAB, so I guess .5psi won't be worth much, what about if I got an air compressor (for tires and such) then charged it up in the back seat (loud as hell, but effective) and had the little line run to the engine, now that would be more beneficial right?

Originally Posted by curtis73

Do a general internet search for things like "leaf blower turbo" or "shop vac supercharger" and you'll get tons of results.

It won't work. Shop vacs make vacuum and flow, not pressure. That "pressure" you feel on your hand when it blows on it is simply flow. As you put your hand closer and closer to the nozzle, there is less and less force on your hand, until you finally cap the nozzle and almost all pressure stops since you have halted the flow.

Don't confuse force with pressure. Force from flow won't help. You need to actually compress the air. Tests have been done a few thousand times. Even the biggest leaf blower or shop vac only makes about 1/2 psi... which does help power on a theoretical level. There was a youtube video showing a civic on a leaf blower and it gained like 3 hp.

But, there is no free lunch. If you want to make that power with a shop vac, you have to have a 120v generator that is capable of about 15 amps. That is the equivalent of adding an 1800-watt amplifier to your stereo. It takes HP to spin a generator... more than you get back with the shop vac. First law of thermodynamics can't be violated. You can't get back more than you use.

[curtis73]

suppose I got a nozzle attachment that got steadily smaller and smaller in diameter to create pressure, then introduce it to the engine at the end?

No. Not a chance. I have done this math a few thousand times for fine folks like you so forgive me if I skip over the details. You can make zillions of psi of pressure. It doesn't matter. The fact of the matter is not the pressure, its being able to supply that pressure while moving that pressure in flow.

Even a huge 50 gallon tank of compressed air at 100 psi would only be able to provide you with 20 psi of boost for about 3 seconds. If you plan on running an electric compressor to keep up with 20 psi of boost, be prepared for these numbers: Your 2.7L engine operating at 6000 rpms and 90% VE ingests about 300 CFM. The top of the line 7.5 hp Campbell Hausfeld air compressor requires 240 volts and 20 amps to provide a mere 27 CFM. Since you require 300 cfm just to support normal operation, you need the equivalent of 600 cfm to be equal to 14 psi of boost.

So... quick math, if you want to support 1ATM boost using an electric compressor you need to magically come up with a generator that can supply 54,000 watts of electricity JUST to support the engine.

So, that means you will need to upgrade your 60-amp alternator to a 4500-amp alternator. That's not a typo. If you want to make a comparison, Generac makes a 60,000-watt generator. It uses a 6.8L V10 engine, and is so big its not even available on a trailer. If you think you can carry that in your trunk, let us know so we can break the laws of physics, too. You have the option of making 121 hp with your 2.7L engine, or you can DOUBLE that power if you simply put a 6.8L-powered 2400-lb generator in your trunk. You have doubled the weight of your car, nearly quadrupled its fuel consumption, and the 242 hp you are now making is wasted on the fact that your anchor of a car has buckled under its own weight at the starting line.

Even if you could generate that much electricity from a belt-driven accessory on your engine, it would require several hundred HP. So, if you want to gain 100 hp from a bolt on compressor, you would need to supply it with about 225 hp of electrical energy.

Like I said before: FIRST LAW OF THERMODYNAMICS. It can't be broken unless you're Superman or Chuck Norris. You can't get out more than you put in. Period. Trust me.. do a search. You can dream all you want, but don't you think that brilliant engineers would have thought of the same thing if it were feasible?


Closed.