what is max boost if both vac lines are off on external wastegate

[ballen1]

could some one tell me how much boost will build up, at wot, of a 20g turbo if both the vac lines to an exteranl wastegate is never hooked up?? I saw a car at the local car club with a brand new tial external gate installed, but he didnt have any lines running to either nipple on the gate itself. he gotta be asking for trouble.

 

[Steve93Talon]

Theoretically, it'll hold shut until there's enough pressure in the turbine side to override the wastegate's spring. He could be running a 7psi spring or a 30psi spring, so it's hard to say exactly what the crack point would be with no boost source to assist it. Either way, it's not correct.

 

[BGGSTin]

He's just regulating with the spring pressure of the TIAL Wastegate, like the previous post stated, it could be basically any boost pressure, depending on the spring that he's running. It's not really "bad," if you know how much boost you want to run, "all the time" then it's not really an issue. The only downfall he would have is not being able to just turn a knob or press a button to change boost pressure, he would have to take apart the wastegate and change the spring.
The only "assist" a boost controller would do to keep the gate shut longer, by intercepting upstream pressure and lowering it before the wastegate.
The wastegates spring pressure is essentially the lowest possible boost that you can run.

 

[Steve93Talon]

You're forgetting one important factor. The wastegate spring would be relevant only to pressure in the exhaust side, not manifold pressure. The two aren't always proportional. I'd imagine that erratic manifold pressure could result. Using a boost source ensures that your gate opens/closes in relation to mani. pressure.

 

[ballen1]

yeah, you guys are right, i understand it now, thanks for the input fellas.

billy