4.6L (1996-2004 Modular) MustangTechnical discussions on 1996-2004 4.6 Liter Modular Motors (2V and 4V) within. Sponsored by Cruizin Concepts
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Well I also purchased a Pro Products intake plenum and 70mm TB just to find out that after install the intake made a horrific whistling sound. I did the same research everyone here did, and found the Tech support people at Professional products completely useless, so after a lot of installing, un-installing, grinding / porting etc, I can say with confidence that the problem is the EGV port that is on the outside curve of the plenum acts like a empty bottle when you blow air over it. (If you look at the Ford plenum, there is a small protruding triangle of aluminum directly preceding the port to deflect air away from the opening.) The new intake plenum does not have that feature, and that is why it whistles. I used several grinding tools and make that port gradually sloped away from where the air is coming from in order to eliminate the sharp edge on the "bottom" of the EGR port. Once that sharp port is smooth, the air no longer gets caught there, hence NO MORE WHISTLE! Be patient and do a bit of port work on the intake and it will be as quiet as the stock one. CHEERS
Take the inlet tube off the TB, hold the throttle all the way open and look and feel to see if there is misalignment between the TB and the plenum that is causing an edge to stick out at the TB/plenum junction, particularly at the bottom.
I had this issue on a C&L plenum with an Accufab TB.
That exposed edge can cause a whistle and is also not good for flow.
See if you can get it to go away by loosening the TB and realigning it.
If not you need to take the TB and plenum off and blend that edge down.
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