Stupid question:

At low, steady rpms (e.g.: idle, 1,500rpm, etc...) what keeps the turbine from spooling and starting the compressor spinning up so that you surge?

E.g. GT3076R Compressor map:



If I take the rule of thumb numbers that Zero_R lists in his "Compressor Map Illiterate?" thread and apply them at 1,000rpm for a 13b, I get 2.9lb/min for a PR of 1 and 5.8lb/min for a PR of 2. Both of these volumetric rates are well to the left of the surge line.

So, is a wastegate configured to not allow exhaust gas to pass the turbine at low revs so that there is no spooling up until the pressure is to the right of the surge line?

Really elementary, I know.

 

There is not enough exhaust/gas energy spinning the turbine at idle and low revs for it too spool. And the wastegate is CLOSED all the time till just before targeted boost pressures are reached.

~Mike...............

 

Gotcha.

So the wastegate acts like any other bypass regulator and you just need to superimpose the turbine map behavior to figure out the spool up characteristics.

 

To generate boost pressure there has to be enough mass flow through the turbine housing.