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Re: Compressor Surge
Real compressor surge happens during spoolup/high boost, not when you let off of the gas. The surge noise in that video is caused by the BOV not letting all the air out in 1 smooth blow. Too tight of a BOV opening and closing over and over might not be the best thing for the turbo, if the air is actually backing up that far, but it isn't real compressor surge and the kind that ported/anit-surge compressor covers are for. People call this noise BOV surge/flutter or "internet surge" because most people on the internet don't know what real compressor surge actually is.
Compressor surge happens when the turbo is flowing A LOT of air and the motor can't actually ingest all that air. A turbo makes boost inside the compressor housing, it isn't like a roots blower/positive displacement blower that works by stacking air in the intake manifold. When air starts stacking up on a turbo car and gets stacked all the way back to the compressor housing, then surge happens. The stacked air starts stopping the spinning compressor wheel or trys to turn it backwards. When you try to stop a compressor wheel going 80,000RPMs, bad things happen.
Compressor surge is common on 2.0l motors with the 61mm turbos. The 2.0l spools the turbo to high boost levels too fast and makes more air than the motor can take in. You can try to get rid of surge by going to a larger exhaust housing/wheel, to make the turbo spool up slower. You can get bigger cams, bigger intake manifold, port the head, to try to be able to take in more air. You can goto a bigger displacement motor that can take in more air each stroke.
A ported shroud/anti-surge cover has passage ways for the backing up air to come back out the front of compressor housing and into your intake pipe to try to avoid reverse flow pressure waves from causing surge.
Basically you can't have your cake and eat it too. If you spool a big turbo too fast you get surge.
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