Imagine what kind of power the SP kits could make if they vented to the atmosphere.

Right now they are routed back into the exhaust. Them seem to be working pretty well with this setup. I am sure there is probably a gain to be had, but it's probably only at super high boost and hp.
As far as controlling boost. I have no problems with boost control on my SP kit. I feel it's more important to have a high flowing wategate than whether or not it's vented to the atmosphere.
I have been in a PHR car that vented to the atmosphere and my SP car that doesn't and the sound isn't that much louder when venting to the atmosphere. It's not at all like my friends T78 on his RX7. When that thing vents to the atmosphere, hide the women and children. It really sucks. I didn't mind it on a Supra.
Later, Steve