Murph said:
So the wastegate determines as what RPM the turbo engages as to not render the engine powerless at low RPM's.
No, not really. The wastegate determines how much boost pressure you're running. i.e. 10 psi, 15 psi, 20 psi. That's all set by the wastegate.
All the blowoff valve does is release pressure in your piping when you get off the gas. If you didn't have a blowoff valve, your plumbing would stay pressurized while you're sitting at a stop light for example. It's just a little device to make life easier for your compressor and plumbing - it has nothing to do with how much boost you're running.
The turbo doesn't have a set "engage" point, it doesn't work like that. The turbo is quite literally powered by your exhaust gas. The reason you have "lag" is because at low RPMs, your engine isn't flowing enough air (and hence enough exhaust gas) to spin the exhaust turbine which is what sets the whole thing in motion. That changes as your RPMs rise, because you're flowing more and more air.
At some point, you'll be flowing enough air to start pushing the turbine wheel around. When that happens it's like a chain reaction... when the turbine starts spinning, which causes the compressor wheel on the other side to start spinning. They're connected by a metal shaft. The compressor side starts compressing the incoming fresh air which makes it denser, hotter and faster. then this fast moving hot air goes through your intercooler (hopefully), and goes into the engine even denser than it was before, and this is what gives your engine the ability to make more power.
Then your exhaust gas comes out faster than it was before, which spins the exhaust turbine wheel even faster... and the cycle continues.
The wastegate dictates how much boost pressure you're running. Not when the boost "kicks in", just how much pressure. When the boost comes on is entirely a function of the way the turbo is sized, and your engine. If you have a bigger engine, that means more airflow at low RPMs, which means it'll spool a turbo faster. A smaller turbine wheel is easier to spool up than a bigger one, so a smaller turbine wheel will let your turbo spool up faster.
Chris Allen's Stage 5 turbo is huge... it doesn't make full boost until nearly 5000 RPM. It takes that much air pressure just to spin the thing up to speed. but a stock Bluebird T25 turbo is much, much smaller... that one spools up by 2500 RPM.
This is just a real general description of how it works. if you want more detailed info, there's quite a few sites on the web, and there's some good books available.
