Surge is while making boost and has to do with the compressor and turbine mismatch that you mentioned, not letting off the throttle. Flutter when lifting the gas and opening the BOV is harmless.

ramsack said:

Surge is while making boost and has to do with the compressor and turbine mismatch that you mentioned, not letting off the throttle. Flutter when lifting the gas and opening the BOV is harmless.

Click to expand...

So your saying surge happens in throttle, and flutter is ok? If that is correct I don't think I have surge and shouldn't worry about the flutter? Some say the flutter is also bad.

Flutter happens when the BOV opens, pressure in the charge pipe drops enough so that the BOV closes, the pressure starts rising again because the turbo is still spinning, then BOV opens, and the process loops. It does NOT force air back across the compressor, which is what surge is. Surge is also placed apart from flutter because surge happens when the turbine is being driven. The only force driving flutter is interia. The mass of the moving parts of a turbo is not enough to cause damage to itself from just building boost. If people can't grasp how feedback loops work, they shouldn't be tinkering with cars (the people who are adamant about flutter being bad, not you, OP).

Made me feel bad at the end of post til I got to the end. Well happy to know I don't have a surge issue. It seems like you pretty much cleared the flutter issue too, unless someone wants to disagree. I still would like to see a video with surge to know what it sounds like if theres a good link out there.(I've seen some on youtube but not a good 1)

I'm sure disagreements will follow at some point

True compressor surge.
True Compressor Surge - YouTube

Some pretty dramatic flutter shown here, which is typically referred to as compressor surge.
sxmuch with flutter - YouTube

True compressor surge is definitely very bad. But whether turbo flutter is actually harmful has always been a topic for debate. However, most can agree that some light turbo flutter isn't a big deal.

I'm feeling better already about the situation being my turbo was recently rebuilt.

Compressor surge is the breakdown in the ability of the compressor to maintain pressure. Air starts flowing backwards across the compressor and mainly bends the blades. It's cavitation. Boat propellers can do the same thing, but it's visually noticeable because gas just instantly appears out of water. It creates shock waves and can destroy props, as well.

Flutter just needs to stop being called surge. It's an insult to people in aeronautics (I may not design airplanes and space ships, but I can understand compressor surge/stall). It's a simple feedback loop. It's no different than an ECU injecting some fuel, waiting for the firing stroke, waiting for the exhaust stroke, waiting for that batch of exhaust to reach the O2 sensor, waiting for the O2 sensor to react, and waiting for the ECU to calculate the new values from the feedback from the O2 sensor. The difference is the speed in which that happens. Electrical signals are fast. Air and mechanical parts are extremely slow.

This is some good info. Thanks man