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question for andre really or anyone

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on a petrol turbo charged car the actuator is always closed until boost pressure is reached then opens when the pressure is reached?

on diesel engines as soon as you start the engine the turbo actuator moves with idle vacum is the opening or closing the acuator at this point? i asume it must be closing it to allow boost to build? if so why is its default position open in that case, if idle vacum closes it?

Correct me if Im wrong but I believe Diesels don't make vacuum since they dont have throttle bodies but I'm not experienced with small diesels only large truck ones. I think diesels use wastegates to affect overall power by using back pressure.

Since diesels do not have a throttle body the same as a petrol they do not pull any vacume at idle...

Instead they have a vacuum pump to operate things like brake boosters etc

Only turbos with variable vane turbines have a vacuum operated waste gate actuator... With the engine off (actuator at rest) the actuator is relaxed, when you start the engine and the vac pump is in action it pulls the actuator up closing the vanes so It can produce boost.

Diesel engines aren't something I am overly experienced with personally. As stated though, many (but not all) diesel engines don't have a throttle body. If the wastegate is a conventional style wastegate then I'd see no reason for it to be naturally in an open position. more likely I would guess Viper is right and the application you're working with is a VATN turbocharger.

Like Viper said the diesel turbos mainly have VGT's now and are either vacuum actuated or electronically actuated. Usually its done to verify range and to set the turbo in the correct position

Also I would like to note its common to see vacuum actuated wastegates on gas\petrol engines more and more these days. It allows for better control and fail safe conditions.