Turbo Compressor Surge VIDEO Compilation
September 23, 2024There are two types of turbo compressor surge. The type you hear when you lift–off the throttle, the other occurs under boost.
The first section of videos show turbo surge under load, the second section shows examples of the more common surge which occurs when the throttle is lifted.
(A detailed description of what turbo surge is and if it’s something you should worry about can be found at the bottom of this page).
Turbo Surge Under Load
Lift-Off Compressor Surge
Explanation of Turbo Flutter
What is compressor surge? Is it bad? How do you stop it?
Looking at the least damaging surge first.
Lift-off surge/BOV flutter, occurs when we have compressed air in the intake piping in front of the throttle body. When we close the throttle, the airflow through the engine drops massively but the turbo is still spinning.
When the airflow through the turbo drops too far vs the boost it’s making, we get into surge. The blades on the compressor can no longer maintain boost (push the air) and air flows backwards through the compressor which causes the noise. When the pressure in the intake drops low enough (not to be to the left of the surge line on the compressor map) boost builds again. But if the throttle is still closed, the cycle repeats, rapidly, causing the repeating “tsu tsu tsu” sound.
Lift-off surge is arguably less destructive because the forces are less (there is less exhaust gas pushing the turbine wheel) but nevertheless, the turbo bearings would prefer it, if there were no surge.
Surge Under Load
Surge under load is more destructive because we have greater (exhaust gas) forces acting on the turbine wheel, because the throttle is open.
The cause is the same as lift-off surge. We are to the left of the surge line on the compressor map, we are trying to make too much boost with too low an airflow volume through the compressor.
Causes
Lift-off surge is caused by the BOV/dump valve/recirculating valve not opening or not opening enough and/or not opening fast enough and/or being too small for the amount of air flowing from the compressor and/or for the engine.
Surge happens under load because the turbo is too big for the engine at lower RPMs and high boost levels. To cure surge under load, the traditional method is to reduce boost at the RPMs where the surge occurs. Hypothetically another solution is to increase flow but this is difficult because our throttle is already open 100%.
MoviChip is working on a surge solution which may make the airflow solution a reality, with the added benefit of reduced intake temps and making more power for the same boost. Subscribe to the newsletter for updates.
Is Turbo Surge Damaging? Should You Fix It?
For sure, the turbo will be happier if it didn’t happen when the throttle was lifted.
And because surge under load involves greater forces acting on the compressor blades, I don’t see a scenario where this is not shortening the life of the turbo
In other words, yes turbo surge is damaging, (maybe a little, maybe a lot) and if you care about your turbo having a long as life as possible, I think it is a good idea to fix it ie stop the surge from happening.
