Turbo Compressor Surge – How to fix it

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First off, what is turbo compressor surge? Turbo compressor surge is an aerodynamic phenomenon that happens when the speed of the rotation of the compressor wheel is too fast versus the speed of the air passing through the compressor. The points where this starts to happen make up the “surge line” on compressor maps.

In other words, compressor surge and the sound it makes, are the blades of the compressor no longer compressing the air. Air pressure is released through the compressor in the reverse direction until the boost pressure drops to a point where the compressor blades can once again compress the air.

When this happens will depend on the engine map but generally speaking it usually occurs when we are asking for higher boost pressures from the turbo at mid to low RPM.

Turbo Wear

Surge puts stress on the turbo bearings due to the compressor oscillating between pressurising the air and the air passing through the compressor in the reverse direction.

How To Fix Compressor Surge

Fortunately it is possible to remedy this issue ie we can stop surge from happening.

To stop if from happening we move our turbo away from the surge line (move to the right side of the line) on the compressor map.

We can’t magically make the engine move more air at the same boost pressure and RPM so we can’t do anything here.

What we can do however is reduce the boost pressure (move down on the compressor map) when the turbo is surging. For example we have turbo surge at 3500RPM and 30PSI of boost, reducing the maximum boost at this RPM will stop the surge. How much the boost has to be reduced will depend on the engine.

In A Nutshell

To eliminate turbo compressor surge we reduce the boost pressure at the conditions where the surge is occuring.

Downsides to the fix?

None really, reducing boost reduces power but we weren’t able to make full power when the turbo was surging anyway. We probably have at least the same power as when the engine was surging, but with the added benefit of less stress on the turbo and a happier engine all round.

Alternative Fix

There is another solution to turbo surge that can potentially allow us to run the same boost pressure as when the surge was occurring and also allow us to make more power for the same boost pressure. A win-win situation. We are about to start researching a product we hope will do exactly this. If you want to receive updates, subscribe to the MoviChip newsletter.

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