Ebay "Superchargers" Rant

[invader166]

Hello everyone,

I've almost reached my wits end trying to explain this someone on another forum, who bough and installed one of those cheap ebay "superchargers" and he claims it made a big performance difference on his car. Honestly, those things are one of the biggest scams I've ever seen, and deserve to a 1-way trip to the bottom of a lake!

Now, don't get me wrong, I actually do believe it's possible to create usable, positive intake pressure with electricity, but only if you're using a properly designed and thought out system!

1. Definition:

First off, I'm sure you all know what forced induction is and how it's created. According to the Cambridge dictionary, a forced induction system is:

...a system in which either a conventional supercharger or a turbocharger, or even a combination of both, is used to increase intake pressure and force a fuel-air mixture into the cylinders of an internal combustion engine.

Also, a turbocharger is defined as:

A ​turbine ​turned by the ​waste ​gases from an ​engine that ​pushes the ​fuel and ​air ​mixture into the ​engine at a ​higher ​pressure, so ​as to increase the ​power ​produced by the ​engine

While a supercharger is defined as:

A blower or compressor, usually driven by the engine, for supplying air under high pressure to the cylinders of an internal-combustion engine.

So, in a nutshell, both turbochargers and supercharges are air compressors, since they increase the pressure and density of the air being supplied to the engine. That cheap ebay "supercharger" is NOT an air compressor, no matter what some people will claim. It's only a fan designed to add more air flow in the intake system. Remember, air pressure and air flow are not the same thing. One will kill you, the other will just cool you down.

2. Design:

Let's look at how turbo's and superchargers are designed create this air pressure:

In the case of a conventional supercharger, this video explains things very well and even goes on to say that fan blades are not good at compressing air: https://www.youtube.com/watch?v=_vaw5zwnhrA

The turbocharger's centrifugal compressor, on the other hand, works a bit differently. This video shows the construction and principle of operation: https://www.youtube.com/watch?v=B5bfyPQgYZY

As you can see from both videos, the construction of both the casings and impellers (and in some cases diffusers) is quite complex, not just a simple fan blade inside a cylindrical rubber tube, as most ebay "supercharger" kits. That's why that "supercharger" cannot create positive pressure, no matter how hard it tries.

3. Efficiency:

Now, as you can imagine, an engine needs a high amount of oxygen from the air to burn more fuel and produce that extra power everyone craves. As such, since the exit velocity of the air from the compressor is so slow, this compression cycle needs to occur at an extremely fast rate. In turbochargers the maximum pressure build-up is controlled by a waste-gate, and in a supercharger, it's being controlled by the size of the pulley that drives the supercharger.
In fact, many, if not all manufacturers, provide efficiency curves for all of the turbos and superchargers they produce. These graphs will tell you how much pressure that particular compressor develops at a given impeller speed. Does that ebay "supercharger" come with one? Most likely not. As an example, here's an efficiency curve from a Garrett GT2052 Turbo:



Doing some quick math, we can see that to create approx. 6 psi of pressure [(14.7+6)/14.7 = 1.4], that turbine would need be spinning at over 80,000 RPM. Something that that ebay "supercharger" is unlikely to accomplish, and even if it did, it wouldn't be able to supply that pressure, because it's not compressing any air! And that leads me to my next point.

4. Required Power:

To compress air, you need power! How much power you need is based on how much intake pressure you want to produce. Superchargers "rob" the power required to compress the air from the engine, while turbochargers use the thermal energy of the engine's exhaust gasses to compress the air.
Assuming that, in order to compress enough air to produce 1 psi of pressure, you'd only use approx. 1 HP or 746 Watts of electricity (unlikely, but let's use if for argument sake), to build 6 psi of pressure, you're looking at almost 4.5 KW of power. And that's only if everything is 100% efficient. With a 12 Volt system, you'll be drawing about 370+ amps from the battery. Not only would that severely drain your battery, but the alternator wouldn't be able to supply enough power to recharge the battery. Somehow I highly dought that's the case with the ebay "supercharger"

And don't get me started on all the other considerations, like inter-coolers, tuning, etc...

Anyhow, that's my little rant, hope you found it at the very least funny.