Ok. I've got sumthing to say here for all of you who upped boost. I feel that upping the boost on the stock turbo is actually stupid. Here's why. We have a tiny tiny compressor housing stock. If you check the flow charts it's maximum effiency is probalby around the 70% area. Seeing how small it is already, we'll say that it's probably tuned for it's peak effiency right at a pressure ratio of around 1.5, not 1.5 bar, but a pressure ratio of 1.5 or about 8 psi of boost. 8 pounds of boost equals about 270 cfm's on our engine at 5500 rpm. Pretty straight forward so far. Now, if we'd look at a compressor map (can't find ANY for the rbh5.. someone help!), we will notice the stock numbers would match up to a nice effiency. Now, plug in 15 psi of boost which would require 360 cfm's. I can promise you that this turbo with those numbers is far too low efficiency to be considered an upgrade. When you lower efficiency, heat goes up, and therefor your density ratio goes down. What we really want here with turbo charging is high density not high pressure. They can go hand in hand, but according to the law of thermodynamics, we cannot increase the pressure ratio the same amount as increasing the density ratio. So, by upping the boost, and loosing effiency, you're probably gettin the same density ratio as a lower number of psi. My advice would be to stick it to around 10-12 psi. Because we're intercooled we do have room for the turbo to be ineffiecent, but still to an extent. And on top of all that, Mazda does KINDA know what they're doing. YES, there's room for upgrades, but upping the boost on the rbh5 much might not be one of them. They wanted a car that's quick, and responsive at low rpm. If they wanted to up the boost, and make the car overall quicker, I'm sure they would of chosen a bigger turbo. That's all I got for today! Let me know if you agree! Peace out.