Episode 45 - Forced Induction

Today I want to talk about forced induction.  That means superchargers and turbochargers.

First the Roots blower.  Blower is the correct term, as it just blows air faster than the engine can use it and builds boost like that.

Blower and a beautiful car

Plus they look and sound cool.http://www.youtube.com/watch?v=uWqdAb_nOow

The screw type superchargers work similarly, but they actually compress the air inside the supercharger, making them more efficient.

Turbochargers are driven by the engine exhaust rather than by a direct connection to the engine, so when you don't need them, they are just there.  That also means, that you have more complex exhaust plumbing to deal with, and you can have lag until the turbo kicks in.

The centrifugal supercharger works like the compressor half of a turbo, but rather than be driven by the exhaust, it is driven by a belt.  There are also ones that have variable drive ratios so they can make more power and low and high RPM, since they usually don't make as much at lower RPM.

With turbo chargers, there are ones that can change the geometry of the turbo on the fly, so it can act like a small turbo at low RPM, and a big one at high RPM so you don't get lag at low RPM, or have the turbo not be able to keep up at higher RPM.

With using a turbo for forced induction, you can run with one or two turbos.  Assuming they are sized correctly, there really isn't any performance difference.  Although with twin turbos, you could run dual exhaust.

There are also set ups that use two different sized turbos, a small one for low RPM and a big one for high RPM.  When the RPM goes up, the small one is bypassed.

A quick note on electric superchargers.  Most of them are crap.  The cheap ones just use a fan that is probably not able to push enough air to do any good.  There are a few kits that are good for short term boost.  So the worse they make it sound in, the closer to reality it probably is.  Also Audi is coming out with an electric boost set up on one of their diesel engines.  What it is designed for is for the split second before the turbo can start creating boost.

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