Vacuum / Boost Reading on Diverter valve lines
 

Today i put a vacuum / boost gauge on the lines that go to diverter valves from the switch over valve.

During idle and let off the reading would go to vacuum 10 inhg. My regular boost gauge would show 20 inhg at idle and let off. So this make me think the switch over valve only allows 10 in hg to open the diverter valves

During acceleration the boost in the diverter lines was the same as the boost being produced. So diverter valves are being shut buy the positive boost pressure.

Hope this info is useful to others.

Now if i put after market BOV on the car will 10 in hg be enough to open them during deceleration?

Interesting info, adding to knowledge pool.

While working on my turbos, I put a pressure guage on the line to my wastegate valves. These use positive pressure from the inlet manifold to open the two wastegates and control boost pressure. The pressure lines are also run via a switch over valve.

I pressurized the line to synchronise the opening of my wastegates. Turbo wastegates are usually pre-loaded by about 3mm, so it takes a bit of pressure to BEGIN to open the wastegate, and rather more to fully open them.

On my car, they started opening at about 3 psi, and were fully open by 7 psi. By presurizing them together, I was able to synchronise the opening by adjusting the rods. Without synchronization, one fo them would have opened first, leaving that bank with less boost and less back pressure. Not suggesting that other people should try to do the same, but it was interesting to see them opening though.

nick

thanks for the info. i was going to do that next!

It depends on how the factory boost control system works. If it's PWM solenoid-based, the difference in actuator length won't make a difference since functionally they will see either zero or full boost and nothing in between.

Older control systems are a simple bleed (either fixed or PWM to "soften" spool up) between the pressure source and the actuator which does start to open the wastegates before the desired pressure is reached. If this is the case, matching the actuators will prove to be useful.

Turbo cars from the 90s could pick up a lot of power under the curve with a manual controller set to stock PSI by preventing premature wastegate opening.

-10 in should be enough to open an aftermarket BOV, especially if it's an adjustable type. You just want to be sure it's closed slightly before 0 so that boost can build properly.

thanks for the pointers!!!

Yes it is PWM solenoid based, but I believe the solenoid valve duty cycle is used to modulate the boost pressure control. The Mercedes M275 Initial Training Information Module page 40 states:

To me, that says the position of the wastegate control rod is modulated by the PWM duty cycle.

Nick

anyone have the link to the M275 training module ?

http://wenku.baidu.com/view/d810de04...3d5bb75ab.html

http://www.mercedestechstore.com/pdf...2008-06-03.pdf

Thanks

Thanks for the link -- I see much reading ahead for the upcoming long weekend!

Just a quick glance shows that these cars really use quite a few factors to determine boost. Some of them are normal in any turbo car but to also monitor oil & coolant temps and even the pressure difference in the intake tract / air filter housing means that troubleshooting a boost problem could get interesting. It's also why they're damn near bullet-proof.

Half you guys are talking about waste gates and the other half are talking about blow off valves. Shardul yes 10 inches of vacuum will be enough to pull up on the diaphram. My Talon has about 10 inches of vacuum with the cam it has and has no problem releasing them. Sorry I have not sent you my intakes or laptop charger yet. Still in process of moving our shop.

thanks for the info. No need to send the charger i sourced one locally for now. Let me know on the intakes :)