caz1562, you're wrong. Air heats up mostly due to being pressurized, and only smaller part due to heat of turbo itself.
Originally Posted by caz1562
Intercoolers do not cool the air heated by the turbo, thats what the exhaust is for
. Air is sucked in via filter, this assists in the drop in temp of the air before it meets the fuel in the chamber charging the air thus giving an increase in power. Once the exhaust gases enter the manifold, they're passed across the exhaust vanes in the split turbo casing to keep the turbo spinning during gear change, this helps keep the turbo charging with air on the inlet side too.
That's the silliest explanation I heard about how turbo works. You picture does explain though how system works (just add intercooler inbetween turbo and intake manifold).
So, easy explanation how turbo works:
First of all, turbo is dependant on ammount of exhaust gasses, which actually force blades to spin. At lower revs there isn't much exhaust gases and that's the 'turbo hole' many people talk of - on diesel engines this means car is 'not moving' under some 1700rpm, when it suddenly picks up.
Another effect of turbo being spooled by exhaust gases is 'turbo lag' which basically means when you're in gear on low, or not throttle and floor it - turbo needs time to spool up and build pressure (by filling pipes, intercooler, and finally have enough positive pressure in intame manifold).
But, back to how it works: exhaust gases spool turbo, and sucks air through intake filter and thru turbo. When air enters turbo it's being compressed (since engine can't take that amount of air) - but while compressing it heats up. Most heat is generated by compression itself, and one smaller part by turbo being hot also from exhaust gases. Due to this, many cars have intercooler through which that air goes and cools down (cooler air = more dense air = for same volume more mass).
By flooring your car, and turbo spinning it could continue to generate more and more pressure, but not to blow your engine there's a wastegate - it is actually an actuator which limits ammount of boost that will be generated. It works in simple way - actuator that moves after there is more than X pressure in intake. By moving, it actually diverts some part of exhaust gasses to bypass turbo - so it can maintain proper pressure on intake.