24-07-2012, 03:45 PM
Known by many different names by people of varying states of idiocy/denial/dribblyism...
Including Jeremy Clarkson infact - numerous times I've heard him say "wastegates chirping/fluttering/chattering" - normally I'm to be found on the receiving end of the television shouting about what a moron he is.
It's Compressor Surge - it's where the airflow demand isn't enough for the shaft speed assembly, causing the airflow to become unstable over the tips of the compressor blades, causing the distinctive noise heard when A. The throttle snaps shut on a petrol - causing the airflow demand to suddenly stop, B. The revs drop very quickly on a boosted diesel - causing the airflow demand to suddenly stop or C. On the throttle, where the engine is spinning too slowly - therefore not much airflow demand/capability with the turbo shaft spinning too slowly - (on throttle surge is HIGHLY damaging to the turbocharger in ANY situation)
It doesn't do any turbocharger any good even if you're off the throttle - people will tell you it's fine, but essentially it's the sound of the air being unstable and not flowing correctly through the compressor wheel, it causes very high axial, torsional and thrust loads on the shaft and compressor, depending on what speed the compressor shaft is rotating at, the worse it becomes. A recirculating or normal blow off/dump/faggot valve will alleviate these problems on a *PETROL* as a general rule, however in some cases, even relieving the pressure cannot stop the noise - on the throttle surge is only fixable either by A. lifting the throttle a bit, or B. getting the correctly sized turbocharger...
You cannot fix this coming off the throttle on a Diesel due to the instantaneous response needed...
Including Jeremy Clarkson infact - numerous times I've heard him say "wastegates chirping/fluttering/chattering" - normally I'm to be found on the receiving end of the television shouting about what a moron he is.
It's Compressor Surge - it's where the airflow demand isn't enough for the shaft speed assembly, causing the airflow to become unstable over the tips of the compressor blades, causing the distinctive noise heard when A. The throttle snaps shut on a petrol - causing the airflow demand to suddenly stop, B. The revs drop very quickly on a boosted diesel - causing the airflow demand to suddenly stop or C. On the throttle, where the engine is spinning too slowly - therefore not much airflow demand/capability with the turbo shaft spinning too slowly - (on throttle surge is HIGHLY damaging to the turbocharger in ANY situation)
It doesn't do any turbocharger any good even if you're off the throttle - people will tell you it's fine, but essentially it's the sound of the air being unstable and not flowing correctly through the compressor wheel, it causes very high axial, torsional and thrust loads on the shaft and compressor, depending on what speed the compressor shaft is rotating at, the worse it becomes. A recirculating or normal blow off/dump/faggot valve will alleviate these problems on a *PETROL* as a general rule, however in some cases, even relieving the pressure cannot stop the noise - on the throttle surge is only fixable either by A. lifting the throttle a bit, or B. getting the correctly sized turbocharger...
You cannot fix this coming off the throttle on a Diesel due to the instantaneous response needed...
