Quote:
Originally Posted by -nexus-
Thanks for that, that looks like a very neat and tidy solution to get the boost line tapped in.
I'm very confused though, how can it not go into vacuum? It shouldn't matter if the throttle body is always open a little (this is how it would be at idle anyway), and it would not be building any boost when off the gas. Coasting off throttle should always produce a vacuum, it would not be producing boost. Where did you get that information from? Happy to be corrected but this really doesn't sound right.
|
This is a very interesting topic. The Valvetronic system that the S55 engine uses does some amazing things. I've looked into this topic a lot and I still feel like I dont have a 100% grasp on how this engine works
edit: took me forever to find this- but here is S55 engine explanation:
http://s3.bimmerfile.com.s3.amazonaw...S55-Engine.pdf The engine does have a "naturally aspirated" mode that can be activated (typically at idle?), which can create a vacuum for crankcase ventilation, but it not the primary operating scenario for the engine. During operation, the only part of system that has any vacuum is the intake pipes between air filter and turbo.
1. The S55 does not pull a vacuum.
• This is why you cannot hook up a traditional blow-off valve (HKS SSQV FTW) or external wastegate to the S55 engine without using a MAC solenoid and controller to open the BOV . The S55 does not even have a blow off valve installed and uses the Valvetronic to regulate excess boost pressure off throttle.
• Since the S55 engine does not make vacuum in the intake manifold (after throttle plate), there is an external air pump bolted to the side of the engine and connected by a drive chain to the crankshaft that creates the vacuum required for the brake booster (and also drives the high-pressure fuel pumps).
2. The S55 engine at idle and under off-throttle deceleration will show zero on the gauge (0psi boost/0 in.Hg). The turbos are always spinning and creating airflow through the engine and the valvetronic regulates how much air passes through the intake valves.
3. The throttle pedal does not control the throttle plate in the throttle body. The throttle plate is only there to help regulate air flow for many reasons. I've attached a screenshot of a datalog of my car. Pay attention to the teal line and light blue line. Notice how the throttle (accelerator) pedal stays at 100% yet the throttle (plate) opening is opening and closing at many different angles independently as engine RPM increases. You can see that when my boost pressure exceeds the boost target pressure, the throttle plate closes down a little bit to help regulate boost but the throttle pedal is still always at 100% (floored). Also, you will see the throttle plate never closes below 20% throttle, even when the throttle pedal is not being depressed at all (0% throttle).
PS: Have you ever seen that video of the N52 engine running and idling WITHOUT the intake manifold at all?