This is not a real answer to the question, but many years ago I rode a Yamaha Turbo Seca (650 cc) on the street. I modified it for more boost by simply capping the wastegate vacuum line coming from the blow-through carb air box. So in effect it made the wastegate so it always saw 0 psi. The stock wastegate limited boost to about 7 psi. I got 14.5 psi out of the completely stock set-up and that was limited by a blow-off valve on the back of the air box. I added oil pressure and a vacuum/boost gage to keep better eye on things. Never had any reliability troubles, only slipping clutches. The stiffer springs made it too much for normal street driving, so I lived with a little slip and stock spring pressure. This could all be hidden by simply plugging the inside of the vacuum line and putting it back on. For me there was no reason to hide anything. I figured this out by understanding the purpose of the air box blow-off, and let that become my boost limiter. I have no idea if the turbo could have made more boost by eliminating the blow-off relief valve on the air box, I decided I was needing it to stay together. BTW, that bike was a slug until the boost came on, the low compression killed the low end. Would be good for land speed racing, but sucked for the street for real serious performance.
