fEArmE

After owning the car for 1.5 years, finally i get to see how the supercharger works!

<iframe width="560" height="315" src="//www.youtube.com/embed/6zKjp_OZN34" frameborder="0" allowfullscreen></iframe>

Mike_L

How is this Audi Supercharger Technology? It works like every other roots supercharger. GM and Ford have been using these since the mid 1980s in production cars. Airplanes were using them in WWI. Audi technology my @$$.

gatorguy7

Exactly. Maybe someone smarter can explain it to us?

dicktahoe

Pretty Basic and doesn't tell us anything really. First of all the video shows Supercharger pressure up to 1.8BAR (1800millibars), however the max that the Audi Supercharger puts out is 0.8BAR--so that's a huge error. There is also no indication of how the bypass valve (and therefore the supercharger pressure) varies as a function of Throttle position and/or RPM and how it affects the HP being produced.

DeerHunter

They are quoting absolute pressure. If you add sea-level ambient pressure (1 BAR) to the boost produced, you end up at 1.8 BAR. At higher elevations, this number will decrease, as superchargers have no easy way to increase boost in order to overcome the effects of altitude. Turbos, on the other hand, will often produce close-to-sea-level power at any reasonable altitude.

Mike_L

Actually, the way Audi cuts boost at high rpm, the computer can easily increase it to keep the same power at high altitudes. Instead of closing the bypass valve, it can just leave it open.

DeerHunter

I'm guessing you meant the opposite, but I get your point. Another way of skinning the cat, I suppose. This strategy will maximize high-end power but will probably do little for the low-end and mid-range, where I suspect the bypass valve is closed all the way at any altitude.

Mike_L

Yeah. Open = less boost, closed = more boost. I'm out of it today.

The bypass is never closed all the way on the A6/A7. Thats their way of limiting power. Closing it all the way increases torque to well over 400 and HP to 380-390, at sea level. Audi limits peak boost to 11.8psi. Given the blowers 1.3L displacement, and maximum rpm of 23000, and the engines maximum rpm of 6100, the blower can technically spin at 3.77x the engine speed. 3.77 x 1.3L is 4.9L per revolution on a 3.0L motor is 1.6 BAR or 24psi at the redline. Of course, that would be with the ideal pulley combination. No idea what size the 3.0Ts crank and supercharger pullies are, but Audi limits the motor to 7psi at redline, far less than its capable of making.

Did that make any sense?

DeerHunter

Mostly. I'm not familiar enough with roots-style superchargers to comment intelligently on your math. I will, however, point out that it's probably an ideal-case scenario. In reality, there are inefficiencies such as leakage between the rotors to consider. In general, roots superchargers are less efficient than a good turbo, meaning that they heat the intake charge more.

As for the limits: I suspect that boost is knock limited (more boost = hotter intake charge = higher propensity to knock) rather than torque limited. Audi engines tend to be pretty stout and it takes a lot to bend a rod.

dicktahoe

OK, so let me see if I understand how this works. The blower is capable of 11.8 psi, but Audi limits it to 7psi at WOT at Sea Level (or 14.7 + 7 = 21.7 psi total) at Max RPM and gets 310HP. That leaves 4.8psi excess available. Now at 10,000 feet elevation the atmospheric pressure is 10.1 psi, and with 11.8 psi available from the blower at max RPM, the engine could still be getting the same Sea-level pressure of 21.7 at/slightly above 10,000 feet ( 10.1 +11.8 = 21.9) by keeping the bypass valve nearly closed.

Is that how it works?