Hey all,
Jim - you're quite right
Wastegates release exhaust gases (i.e. "gates" the "wasted" exhaust) so that the turbo doesnt spin itself to oblivion (remember, turbos can spin up to over 150,000 RPM!)... Also, it controls the boost pressure (pressure of air in the inlet system). If the pressure continues to build, you get huge amounts of air in the engine cylinders, which (assuming there is enough fuel) you get a continous power build up until the piston rings rupture (or the pistons melt!), and the engine becomes very sick
However, something else usually happens before that. Basically, you end up with an excess amount of air versus fuel (the "perfect" ratio is usually 14.7:1, and this is known as the stoichroic ratio), because the injectors reach their maximum capacity and cant flow anymore (or the ECU doesnt supply any more fuel because it doesnt know about the excess air). This is called running 'lean', and most engines do this a little in the midrange RPM for maximum power, and usually a little rich (less air than the stoichroic ratio) at the extremes (idle and redline) for safety. If an engine runs excessively lean, this is where the most damage occurs. Pistons, cylinders, crowns, and spark plugs can all crack, temperatures can rise dramatically causing warped engines, etc, etc.
Personally, I think playing with wastegates should only be left to people that know what they are doing (cuz of the above scenarios if you get it wrong), but you can adjust it yourself if you really wanted to. For safety, I'm not gonna explain exactly how this is done here, in case of problems! The best way to increase your boost pressure safely (and reliably) is to allow someone to re-map your ECU. I havent really investigated yet, but I know Superchips does a re-map for it, and produces a claimed 24BHP additional horsepower - but ultimately you can probably expect a little more. Probably quite a few other companies can offer this as its basically the same engine as the Astra Coupe Turbo.
As for DV's, the VX definately has one - and it's probably a recirculation type (known as a Diverter Valve), as the car uses a Mass AirFlow meter (MAF sensor). Atmospheric types (known as a Dump Valve) dump all their air, so it's not closed loop, and the ECU loses track of whats going on.
Hope this helps!
Thanks!
Shash.
PS - Hi Thorney!
Edited by Emmy, 25 May 2003 - 11:34 PM.