BOV vacuum line
 

I recently found out if you remove the vacuum line to the BOV you get a turbo flutter with the stock twins just wondering if it’s safe to cap it off at manifold and BOV or will I lose boost and cause engine damage thanks

You're asking if you remove the function of an essential component will you hurt something?

I also found out I can hear cool sizzling sound coming from the engine bay if I drain all the coolant before a quick spin around the block, not sure if that's bad for the engine or not tho.

COMPRESSOR SURGE.
-Ted

Only thing I can think of that might be detrimental are thrust loads on a journal bearing turbocharger, which the OE unit(s) are, so it may be beneficial to do some research on that. When the throttle plate is closed, there's nowhere else for the air to go but back out.

IMO I think blow off and recirculation valves are non-essential to the function of the system. You'll have a lot of folks telling you that they're absolutely necessary but are not able to explain as to why or may suggest that it increases the transient response of the turbocharger. While they may be correct, no one that I know of has data that supports such a notion. From what I've been able to discern from my research, the only function they serve (In the scope of OE manufacturers) is to lower or eliminate the noise created by the phenomena I made reference to above. If you look at forced induction systems on professional level endurance race vehicles (where obscene sums of capital are wrapped up into completing the event), you may be hard pressed to find a BOV, as noise mitigation is much less of a concern.

Here's a link to a thread posted by arghx, who is one of the more knowledgeable members here and does similar work for OEMs. It's about as "scientific" as we can get with the resources we have.

https://www.rx7club.com/single-turbo...-valve-884695/

I've noticed this is the new "cool" thing to do. Lots of youtubers doing this for the flutter sound of compressor surge. Call me old but the sound of an uncirculated BOV venting to atmosphere or an aftermarket BOV used to be the "cool" thing to do.

I have no technical background but hesitant to take too much away from what they do on race cars and apply it to my street-driven mildly modded car. Teams intend to replace or rebuild nearly everything on a professionally raced car in between each event. As you said, they have obscene amounts of capital to do that. But I’m hoping to continue in my old age with the stuff I have as much as fate allows. To maximize response they have little to no air filtration too. But long term that might be detrimental and I wouldn’t be inclined to adopt that either.

I only added that example because those cars tend to do more mileage in a span of 24 hours (with air filters, no less!) than most of us will do over a period of several years.
But yes, for the street driven twin-sequential third gen, I'd leave it as is.

Yeah, I figured we were on the same page. My post was more for the OP’s benefit. So he wouldn’t think ‘well racers do it so it’s gotta be cool’. IMO it’s just silly for multiple reasons.