I have done some searching on how our wastegate, BCS and BOV/bypasses work, but havent been able to piece it all together. Can someone please answer these questions or direct me to a thread/link that tells me how it works on our cars


turbo----------/
...................T-------------BCS-------intake
Wastegate--/


So, under full throttle

When does the wastegate activate and where does it vent the turbo pressure to?

I am assuming that the wastegate activates and releases pressure when the turbo spools and generates a certain amount of pressure.

Does the BCS moderate this pressure (in response to electrical signals from the ECU) by venting the line pressure into the intake until it decides ok, fun is over, youve boosted enough, Im closing of the intake so the WG sees lots of pressure and vents the turbo pressure, thereby stopping too much boost? or do I have this back to front.

As for the bypass valve. Its vacuum source is connected to the intake mainfold. So it does nothing until

a)you close the throttle after being at WOT and all that pressure in that just built up in the intake mainifold cause you closed the throttle plate, tells the BOV to vent the excess pressure back from the mainfold intake into the air intake.

b) if you got an MBC on and are trying to boost more that the stock BOV can handle, it will also vent.

I looked at the vacuum routing diagram under the hood, so I hope I have this right.

Please help

 

It would take more words than you're probably willing to read to fully explain how the system works, so in minimal detail, here goes...

The turbo has two sides, an intake side and an exhaust side, and they are tied together by a solid shaft that connect the two. The intake side sucks air from the airbox and compresses it, and sends it through the intercooler, passed the throttle body, into the intake manifold and subsequently into the engine. But to compress the air going into the engine, you need an energy source to do this. So the turbo "recovers" some of the energy from the exhaust gasses coming out of the engine to drive the compression that forces the air into the engine under pressure. The turbine wheel in the exhaust side of the engine(sorta like a simple fan you use at the house that pushes air, only it's operating opposite of that), is tied to a compressor wheel (similar design) that is in the intake. As the exhaust gas comes flying out of the engine at high velocity and hot as hell out of the engine, it has to pass through the turbine wheel and a very tight housing, which makes it spin really fast. And, since this is tied to the compressor wheel on the intake side, that's where you get the energy to compress the air going into the motor.

A wastegate "bypasses" the turbine wheel, in essence diverting the exhaust gas away from the turbine wheel and dumpingg it directly into your exhaust system without having to go through the turbine wheel and tight housing. All (or most) of the exhaust energy is wasted out the tail pipe, and you don't have the driving force to compress the air on the intake side.

So the way it works is, the boost control solenoid is in control of how much "signal" is sent to the wastegate to force it to open and divert the exhaust energy away from the turbine wheel. Boost is too high, wastegate opens and diverts gas away from turbine... boost is too low, and wastegate is fully closed and forcing all exhaust gas through the turbine/housing making it spin really fast, which in turns spins the compressor wheel to make more boost. The boost control solenoid gets compressed air out of the intake manifold, and will either divert it to the wastegate (to make it open and limit boost), or dump it back into the intake tract (which keeps the wastgate closed) so that more boost is made.

The bypass valve is located in the intake side of the turbo instead of being like the wastegate in the exhaust side. When the thottle body closes, the intake manifold goes under a heavy vacuum, because the engine is still turning, trying to "suck" more air in, but it can't because the throttle body is shut. The turbo is still spinning really fast from all the exhaust energy coming out, and it doesn't stop on a dime (objects in motion tend to stay in motion), so it's still making boost. Problem is, it doesn't have anywhere to go. This will "stall" the turbo, or slow it down really quick since it can't move the air forward due to the closed throttle body. This is very damaging to the turbo. So the bypass valve takes a signal (a low pressure source) from the intake manifold, and essentially gets sucked open, so that the compressed air coming off the turbo has somewhere to go, and it gets recycled back to the suction side of the turbo in a simple loop. When you hit the gas again after a shift, the turbo is still spinning really fast because the bypass valve kept the turbo from stalling, and you're back in boost really quick.

Hope this helps clarify things.

 

Awesome, that is really informative I truly appreciate it.

I had a couple more questions that hopefully you or someone else could answer..

1. Our cars dont bulid boost in neutral. Is that because the ECU tells the BCS to leave the wastgate open to stop the turbo spooling?

2. And with an MBC installed on our cars, they work by only allowing the wastegate to see pressure once the limit is reached by the spring in the MBC. The spring opens and then allows the pressure to flow from the turbo nipple through the MBC and then to the WG, which opens. Right?

I will be helping a buddy put a turbo kit on his Z in a few weeks time, so hopefully the knowledge learned here will help down the road