Got a question for you guys that know the boost. Is the boost level a fixed setting in the external wastegates? I have been looking and reading around the net for a while now. It seems like there is a spring in the wastegate that controls when the piston in the wastegate opens or not. Then there is another type (also external wg) that has the spring inside but also fittings outside them to allow hookup of vacuum lines or something like that.

Reason I am asking is because I am planning to use a boost controller that is adjustable from inside the car. Boost high when needed and run normal when cruising. I believe that the vacuum lines hook up to the boost controller to control the wastegate. Correct me if im wrong.

So, can someone identify to me what brands or models that have the lines to hook up to a boost controller.

My friend is going to sell his TIAL 38mm(real unit, not imitation) wastegate to me. I want to be able to hook up a boost controller. Please some help here?

Thanks!

 

Internal and external wastegates both work the same way. They by-pass exhaust flow and energy around the turbine. This controls how much power the turbine makes and in doing so how much power to turn the compressor.

Internal simply means that the WG valve is contained in the turbine housing. External means that the WG is a separate casting with the valve inside.

A WG has a spring that holds the valve closed. When closed all the flow goes through the turbine. The WG also has a sealed area that contains the spring and an air tight diaphram. Attached to this chamber is a small fitting to which boost pressure is fed via a pressure line. This boost exerts pressure on diaphram. This boost works against the spring pressure. When the boost is overcomes the spring pressure the WG valve opens and exhaust gas energy bypasses the turbine... viola, boost control.

This boost pressure comes from the intake system usually from the intake manifold itself. The spring holds the valve closed until the combined pressure against the valve head from the exhaust and the pressure from the intake is enough to start opening the valve. The spring and pressure chamber together are called the actuator. On an internal WG the actuator is usually bolted to the compressor side and controls the WG valve with a metal rod. On an external WG the actuator is usually contained withing a chamber bolted to the valve port.

Changing to a spring with a different strengh or having an adjustment to change the spring tension against the valve are 2 ways to control the valve opening relative to the boost pressure. To add convenient adjustment you can add an air bleed in the line from the intake manifold to the WG actuator. This effectively reduces the amount of boost pressure reacting the actuator and delaying the valve opening until a higher intake manifold pressure is reached. The bleed can be very simple or a computer controlled valve.

Some wastegates have a second port. This port works supplies vacuum or boost to the side of the spring that holds the valve closed. This can be used with certain computer controlled boost controllers to achieve very precised boost control.

 

Good stuff.

May I add, that a lot of times the boost reference for the Wastegate usually comes from a nipple that is right on the turbo compressor housing.

 

Thanks.

I also just reworded and expanded my explaination above if you care to edit your quote to include the new verbiage.

On internal wastegates you are correct. A fitting is attached to the compressor outlet and is connected via a vacuum/boost line to the actuator. This factory arrangement is the most basic and is the first thing to modify. Boost pressure at the compressor outlet is very frequently higher than the actual boost pressure inside the intake manifold due to pressure losses through the plumbing, intercooler, throttle plate, etc.