Thanks for the link. I must admit that I have spent way, way too many hours snooping around the vast quantity of high quality info available on TDIClub. It is easy to get addicted to that forum if you are an info junkie.
It's called compressor 'surge', and it's a major problem for turbo manufacture. Basically you're expecting the impeller to try and push air 'that isn't there'. The motor is runnung at low revs, there's a lower air flow, and you ask the inlet impeller ( cool side ) to boost. To my understanding, it starts to cavitate, not unlike an outboard motor that isn't in deep enough. The output oscillates, and puts tremendous stress on the turbo shaft, and it's in the surge area that impellers often shear off. Now most cars are tuned so that the potential to produce turbo destroying surge is small, but it's still possible.
Add to that the amount of soot and thus wasted diesel you're producing below the 1700 ish RPM boost range, and it's simply a good place to avoid. If I'm crusing in 6th and notice the revs drop below 2000rpm, I go up a gear. Bottom line is avoid high throttle / lagging the engine. Use the gears!!
Here's a technical explination that's far better than mine, and will give Obi Dobe a hard-on.
http://forums.tdiclub.com/showthread.php?p=417918
2014 Skoda Yeti TDI Outdoor 4x4 | Audi Q3 CFGC repower | Darkside tune and Race Cams | Darkside dump pDPF | Wagner Comp IC | Snow Water Meth | Bilstein B6 H&R springs | Rays Homura 2x7 18 x 8" 255 Potenza Sports | Golf R subframe | Superpro sways and bushings | 034 engine mounts | MK6 GTI brakes |
Thanks for the link. I must admit that I have spent way, way too many hours snooping around the vast quantity of high quality info available on TDIClub. It is easy to get addicted to that forum if you are an info junkie.
2017 MY18 Golf R 7.5 Wolfsburg wagon (boring white) delivered 21 Sep 2017, 2008 Octavia vRS wagon 2.0 TFSI 6M (bright yellow), 2006 T5 Transporter van 2.5 TDI 6M (gone but not forgotten).
Very close & nearly right on the money cogdoc
Actually compressor surge is (quoted directly from Garrett)
The surge region, located on the left-hand side of the compressor map (known as the surge line), is an area of flow instability typically caused by compressor inducer stall. The turbo should be sized so that the engine does not operate in the surge range. When turbochargers operate in surge for long periods of time, bearing failures may occur. When referencing a compressor map, the surge line is the line bordering the islands on their far left side.
Compressor surge is when the air pressure after the compressor is actually higher than what the compressor itself can physically maintain. This condition causes the airflow in the compressor wheel to back up, build pressure, and sometimes stall. In cases of extreme surge, the thrust bearings of the turbo can be destroyed, and will sometimes even lead to mechanical failure of the compressor wheel itself.
Common conditions that result in compressor surge on turbocharger gasoline engines are:
.A compressor bypass valve is not integrated into the intake plumbing between the compressor outlet and throttle body
.The outlet plumbing for the bypass valve is too small or restrictive
.The turbo is too big for the application
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