ok guys, listen up. As an engineer with a heavy background in thermodynamics I am going to show you some of the math behind this, along with some basic thermo so it'll be somewhat understandable. It's going to be long and maybe boring, but read through it in detail before firing back with a response.
A turbo or supercharger is a compressor.
The particular volume of air that we are compressing will be referred to as a "control volume". We will basically think of it as a particular mass of air as it moves through the system, the unit doesn't really matter except that no mass goes in or out, and we have an imaginary boundary around this control volume.
A pound of air at 10psi has a higher internal energy content than a pound of air at atmospheric pressure. To increase that energy, work must be put into it. That work is what achieves the compression, and that work must come from something, whether it be the engine through a belt, an exhaust turbine, or an electric motor.
So here goes - Through some calculus and thermo equations you can arrive at an equation that expresses the work performed on a control volume to achieve a particular change in pressure or volume - compression or expansion. This same equation can be used in a reciprocating compressor - or internal combustion engine. It doesn't depend on how the control volume is compressed - just the initial and final conditions.
W=P1V1*ln(P1/P2), where P1 and V1 are the initial pressure and volume, respectively, and P2 is the final pressure. This comes from combining the differential equation W=PdV with the ideal gas equation PV=mRT, and integrating.
I'm using the metric system because this stuff is easier for me that way...
P1 and V1 are atmospheric conditions. P1=101.325kPa and V1 is the specific volume, 0.844m^3/kg. 1psi is equal to 6.895kPa, so if we're shooting for 2psi of boost, we want a final pressure of 115.115kPa.
Plug those numbers into the equation and you get -10.9kJ/m^3 - which means we put 10.9kJ of energy into each cubic meter of air in order to compress it from atmospheric pressure of 14.7psi to our boosted pressure of 16.7psi.
Now we take the flow rate of our engine. Since we don't know the volumetric efficiency of the engine, I assume 90%, with a 3.0L and a maximum RPM of 5500. That works out to .1375m^3 per second, which multiplied by our energy per cubic meter gives us 1348.875W, or 1.81hp.
So - that means it takes 1.81hp to create 2psi of boost on a 3L engine, assuming 100% compressor efficiency. So we need a 2hp motor, not 1hp, and most electric motors are in the 75% efficiency range, so we'll be pulling about 2.4hp worth of electricity, which works out to an amp draw of 134A assuming an electrical system voltage of 13.4.
So, YES it is possible. Now for the practicality.
134A is huge even for an aftermarket alternator.
You won't want to boost the engine all the time, and clutching it like an AC compressor would shock the engine and create very poor driveability. The best way to modulate compressor speed to prevent overboosting the engine at low RPM would be a variable speed motor, computer controlled, that could modulate compressor speed according to inputs from the MAF, TPS, engine speed, etc. This would of course require a controller and a variable speed motor.
In my vendor catalogs at work I only managed to find 12VDC motors up to 1hp, and even that weighs 44lbs and is 7" in diameter, and retails for $1298. That's not even variable speed, which would likely more than double, maybe even triple the price.
The relationship is not linear (for example it only takes 10hp to make 15psi of boost) but at low boost levels the hp to psi relationship is linear enough that 2hp=2psi and 1hp will net you about 1 psi...but we're still pulling 86A which is a LOT of current, and that 86A will be putting a load back on your alternator equivalent to 1.5hp, so your 10hp gain just became 8.5 - and we're still assuming a compressor efficiency of 100% which would really be no more than 60%...and now we're down to only being able to realistically expect about a 5hp gain. There will be a power loss associated with the temperature rise from the entropy generated in compression, but I don't feel like calculating it. The 100 pounds you added in weight will eat up another 4hp. In my opinion that's pretty conclusive that a 1hp compressor is just not enough to benefit. You'll have more gains leftover after the parasitic losses by using at least a 2hp motor, but then you start needing extra batteries to provide the current so it gets expensive quick. You could have a battery bank in series to create a higher voltage, which significantly widens your motor choices and lowers your amp draw, but it would have to be separate from your main electrical system so you'd have to charge it at night.
So - the reason it's not commonly done is because of the cost to benefit ratio. A turbo or supercharger will run about the same, perhaps less cost and the power gains are enormous in comparison. A 5hp gain is something you might get out of a freer flowing exhaust and intake, maybe some dyno tuning.
If you want to do it to be different, by all means go for it. You might actually pull it off, and it might work. Just don't think you're doing something groundbreaking that will change the face of the auto industry forever, and don't expect the kind of gains you'd get from a conventional forced induction setup, or you'll be sorely disappointed.
I think this should sufficiently show that for anything less than 2hp, you're wasting your time, and anything 2hp and up isn't cost effective compared to the alternatives.
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Not to mention I work with compressors every day as an A/C and refrigeration engineer.
