same sound just mine happens right at 0-5 psi positive pressure

It is not just happening 2500-3200 rpm it’s happening through most of the rpm range in first if at wot after transitioning from negative to positive pressure and the beginning of second at wot. Once the weather drys out on the east coast I will post a video showing the issue.

Yes the bov spring is correct, I even tried one step softer the 8-11in/hg spring with the same result. I’m pulling 14.5 in/hg at idle and have the 12-15 in/hg spring in the bov when I made the original post and currently.

I have built many turbo Honda’s I’m not new the the forced induction world and have assisted many others to properly configure systems over the past 20 years. I know the importance of the correct bov spring. My current setup has NO THROTTLE LIFT surge at idle or from wide open throttle to no throttle when driving the car hard or soft. The BOV is very responsive the sound is clear when driving.

Unless the new Defi (not a cheap gauge) vacuum/boost gauge is incorrect it’s 14-14.5 in/hg at idle when warm less when cold. The bov vacuum source is sourced directly on the intake manifold main plenum and is a -4an line to the Bov. The wastegate pressure source is also a -4an line a foot after the turbo right before it enters the intercooler (2.5 inch intercooler piping hot side and 3 inch intercooler piping cold side.)

I pulled this photo from a video I had

The 14.5 in/hg the car pulls at idle @ 1200 rpms or so when warm. The tuner was surprised how easy the car idled compared to other gsc t1 cams he has tuned in the past. The car didn’t exhibit any of the noted flutter on the dyno when I got the break in tune done and car made good numbers on a very conservative tune (I like to break in a new clutch/motor some before pushing it on the dyno). I had a fuel return issue that was found when the tank got lower aerating the fuel and we stopped tuning then...I put the car on the trailer to take it home to put some miles on the components and install a longer return hose on the fuel pump holder...We also verified no vacuum leaks at intake manifold gasket (hondata) and injector gaskets (new) on intake manifold the most common leak locations as you probably know when it idled easily.

the wastegate source is on the intercooler pipe there is a bung welded on the pipe a foot or so after the turbo and 1/8 npt to -4 an fitting then a 2 ft ptfe -4 line to wastegate. I eliminated the Mac valve just to retest without the extra t and lines and issue was the same. Boost pressure creeps a little up high like would be expected with top mount and large turbo and single gate but is steady in higher gears 3,4th and 5th

the Defi gauge gets its pressure source also from the main plenum on the intake manifold and is a smaller diameter quality silicone hose 1/4 inch I believe only a few feet long.

I have always used either a tapped turbo housing or a pre throttle body source for the wastegate pre or post intercooler. I know that tial says that the wastegate shouldn’t be post throttle body did they change that? Bov post throttle body but wastegate pre

taken from Tial's website:

Make sure that you are using only a boost pressure source. This can be found anywhere between the turbo compressor housing and before the throttle body. Do NOT have the boost pressure line plumbed in to the intake plenum. The intake plenum has both boost pressure and vacuum at different points. Vacuum can damage the diaphragm in the wastegate housing.

I have read that near the turbo the air flow could be turbulent and that post intercooler is best giving the air flow time to stabilize.

Post form Tony the Tiger

It’s worth a try moving it to the intake manifold I just don’t want to damage the diaphragm on the wastegate from the massive amount of vacuum the engine sees post throttle body 30+ in/hg on hard decelerations. Maybe a one way check valve would work (high flow)