| This is great stuff Ash. I am glad that you are engaged in this one. Referring to your paragraph 10 : Consider when the valve spring preload varies. At really high preloads it will require many psi more force applied to the valve's inner face to force it open (the face that is exposed to the charge air in the induction pipes). This will cause the valve flutter to occur earlier in the blowoff event, which should be obvious, but there is also another effect; it will cause the valve to stay closed even when there is a few psi of pressure "left over" in the charge pipes, of which it will not vent. This ultimately will cause compressor surge, the "real" compressor surge. I agree completely. In fact, in my car, I experienced "the flutter noise" with the GHK recircs (higher preload) not the stock recircs (lower pre-load). It is clear that in my case, the higher preload is causing the noise. The question remains as to whether "the flutter noise" is valve noise or surge. You just asserted that the noise is ... "...compressor surge, the "real" compressor surge." Referring to your paragraph 11: Now before you get all into a tizzy to say that this contradicts my original explanation, you will have to take a step back and weigh this out. Even though the compressor does experience surge in this instance, it is not the severity of surge that will cause rotorbearing damage. You will hear the distinct noise this creates - a buffeting of air - shuh-shuh-shuh-shuh, with a corresponding low-frequency resonant howl at those same intervals. Ash, my old friend, you KNOW I love a good tizzy - LOL. I do agree that you COMPLETELY contradicted your original explanation so thanks for saying that before I had to :-) However, I also understand your larger point regarding severity. I pursued this because I was curious and I was concerned that I was potentially seeing compressor surge with my new set of mods. However I never asserted, nor did the Flutterdump vid, that this was the type of major turbo killing surge that we should all panic about. I can accept that it is likely "non-terminal" especially with the number of miles per year we put on up here. That said, here are my issues with the surge and why I chose to not just "live with it": 1) The whole point of the recirc is to keep the turbo spinning freely and retain the compressed charge that you have already "paid for". If the preload in the recirc is causing surge, it defeats the whole purpose of the recirc IMO, especially on a 5 speed. 2) When I replaced the GHK recirc with a stock recirc, the surge was eliminated, AND the car spooled noticeably better coming off of a shift. (I recognize that the second point is subjective, and may also be skewed by my relief that the noise was gone). So I am asserting that there is a (non-terminal) performance dis-benefit to living with surge. 3) The noise. Here there is a trade-off - Goose Honk or Flutter. The noise is quite likely specific to a cars mod list, sound-proofing, age, etc. Goose Honk or Flutter is a matter of personal preference. In my case, the flutter is way more annoying than the goose honk. And finally, to satisfy my curiosity once and for all, I will remove the stock recircs, block the pipes, and see what happens. If the flutter noise returns, then it clearly must be surge. If is eliminated, it clearly must have been from the recirc valve. I will post results. Thanks for adding some additional clarity.
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