Actuator opening pressure vs boost pressure
Turbo Mini Forums

The actuator that came with my turbo starts to open at 12psi; how close to this should I expect the boost pressure to be?

If I want to set the boost lower, what are my options? Are they easy to mod, or do I need to fit a different one?

it depends on a few things, its usually some where between the starts to open and fully open pressures,
the bigger the wastegate port the closer to the starts to open pressure it is,
the longer the lever on the WG arm the closer to full open pressure

Yes i moved to the darkside

Instagram @jdm_brett

I find it usually around where it cracks opem at a half hole preload sometimes slightly less. Obv there are a tonne of variables but oft overlooked is the force of exhaust gasses on the wastegate flapper. Certainly the static pressure when the gate atarts to crack open will be within a couple of psi of where it will run on your average system imho.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Starts at 12, fully open at 24 psi. Turbo was intended for deisels.

Port is 18 mm diameter and not very well shaped although I could make a fair improvement with a die-grinder.

that with a half hole pre load phil ?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

No, the rod wasn't attached to anything. I think it should open around 15 or 16 psi with a half hole; Would that be closer to actual boost?

I wasn't intending to run that much boost from the start. Is it feasible to open these things and modify? Construction is 2 pressed steel halves, one half with a lip curled around the other half to seal.


Start to open 12 psi
Fully open 24 psi (at 12mm extension)
Open rate =1.0mm/psi
Hole diameter 7.5mm
Wastegate lever length 19mm
Wastegate port diameter 18mm (plenty of room to open up and improve porting)

Edited by PhilR on 12th Jul, 2015.

Install the actuator to the turbo.

And then yes, at whatever test pressure the flap valve starts to open, this is approximately the boost pressure you will see.

There are other variables, but the above will almost always apply. As to whether that behaviour will remain the same at different engine loads, again that comes down to the many variables.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

cant the pre load on the gate be reduced?

yeah but it doesnt net you much adjust-ability, going by the figures thats a 1 bar actuator, seems to be a pretty standard size for diesels. if you cut open the lower half of the gate from the seam you may be able to play about with the spring but I cant imagine there is a neat way to do it, if you tamper with the seam you likely wont get the diaphragm to re-seal as im sure it is retained by the seam

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Just fit a softer actuator from something else if you want less

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will