https://www.rx7club.com/showthread.p...hreadid=263431

It seems to me that in the link above it states that after installing your rb exhaust system your boost goes up to 11 PSI and after the turbo is ported the boost goes back down to ~6.5. I've always heard, and seen stated on rb 's website, that after installation the car will boost 10-11 psi.

Racing beats web site
http://www.racingbeat.com/FRmazda2.htm

 

Freeing up the exhaust flow and releasing back pressure allows the turbo to spool faster and higher. The boost will creep up to 10-11psi or higher depending on other mods. The stock wastegate cant control that boost because it is too small. It can only vent off the excess boost up to the stock wg diameter. This is why you port the wg larger than the diameter of the stock wg flapper and weld on a larger flapper.

If you port your wg large enough you will able to control your boost and it wont creep. If you get the necessary fuel mods you can get a boost controller and up the boost back to what level you want.

Here is a link to wg porting: http://fc3spro.com/TECH/HOWTO/KWG/kwg.html

It should be a little different flapper design since you have an s4.