What determines the point where the turbo cuts in??

Revs?

Exhaust flow?

Weight of right foot?

all of the above?

Jono

revs... all 2K of them.

Really? it cuts in as low as 2k?

Really? it cuts in as low as 2k?

Max torque on Octy vRS from 1950 to approx 5000rpm,so they say.David

Really? it cuts in as low as 2k?

Yup, it actually cuts in at less than 2k RPM. What you have to remember is that the 1.8 turbo is (officially, at least) a "light pressure turbo" engine. The turbo is small, it spools up fast, and can provide substantial boost at low engine revs.

In fact, the stock ECU spends most of its time holding back the turbo (by modulating the wastegate) to keep boost levels down to the factory-set levels. Of course, this is exactly why the 20v turbo engine lends itself to tuning...

If the turbo is a variable vane type turbo its the actuator that determines when the boost cuts in.

The VV Turbo doesnt have a wastegate like a traditional turbo. The actuator rod is linked to the turbine blades in the exhaust side of the turbo. When less/low boost is required the blades are allmost parallel so the exhaust gas passing by them has little effect as there is'nt much surface for them to push on. As the actuator rod moves and opens up the blades more surface area becomes available and the turbo speeds up.

The main advantage of this is that at slow speeds it acts as a small low inertia turbo but as it speeds up it becomes a larger unit producing more boost.