Hi Ghost, I am experiencing the same issue. Also, when I first start it up some times, the engine revs like i was pressing on the gas pedal. Have you resolved your issue?
Funny you mention GT Mustangs. I had a guy pull up beside me and tell me I had a really bad manifold leak. So ...when the light turned green, he left quickly. I got up beside him at 40, and said...listen to this. The manifold leak sound disappeared, but the roar of motor and tire appeared. I left him behind me. At the next light he said, I'm selling this and buying one of those. I love my street snake. Oh ya...this thread is about blow off valve size...lol. I am looking into a unit at Amazon right now...too many options...lol.Mine also does that too. But not real bad. Just blip the accelerator and shes fine. The real problem is that my mpg calculator has messed up. Does not calculate correctly. Says im getting about 8 to 10 mpg more than it actually is. Has anyone experienced this problem? That being said, with the power it has now I would do it all over again. I am 3-0 in roll on drag races. 2 vets, 1 GT MUSTANG and not the sissy mustangs.