Red 944

Right now without any sort of boost control and the Tial with a .8 bar spring .. naturally the wastegate lets go at .8 bar.

If a controller is added can a maximum boost be maintained instead of letting go when the boost peak is reached?

SoloRacer

Without a boost controller the wastegate sees the actual pressure in the intake manifold. When the boost gets to the rated pressure of the spring the gate opens and dumps the exhaust. The boost controller is installed between the pressure in the manifold and the wastegate and controls the pressure (or signal) that the wastegate sees. With a boost controller installed the pressure in the manifold is no longer directly getting to the wastegate. The boost controller only allows the pressure to open the gate when it decides it needs to be open. The wastegate spring then becomes the lowest peak boost level you will make (if you are seeing too high boost levels adding a boost controller will not help you. You need to change your spring or get a bigger wastegate). With a boost controller you can increase the boost higher to whatever maximum the turbo is capable of sustaining. When the maximum boost is reached the boost controller will dump exhaust until boost is reduced to just below maximum and then close the line to let boost build again back up to the maximum. This oscillation is what holds the boost level. An electronic boost controller has a smaller oscillation than a manual boost controller and thus should be more accurate.


Are you using a stock turbo and stock wastegate? If so the exhaust back pressure may also force the wastegate to open earlier than you want.

Red 944

I've got a Tial 38mm and a SFR stage III turbo for reference. So if the boost is set to 13 pounds it will go 13,12,13,12 (example) .. how much would it drop between oscillations?

SoloRacer

The oscillations are much smaller than that. It's more like 13.1, 12.9,13.1.....etc. They are also happening really fast. I can hear the solenoid on my Greddy Profec B and it sounds like a zipper. On your gauge it will show a steady 13 psi

Danno

Red, the range and speed of the oscillations depends upon the boost-controller you're using as well. Mechanical controllers typically can have a feedback cycle of about 3hz and a pressure-range of about +/- 0.75psi. Electronic controllers are much faster and can cycle about 10-15h and pressure won't vary more than +/- 0.1psi.