Originally Posted by smakdown

Im no expert on turbos but as I understand it the whole point of lowering the compression when going turbo is not for power purposes but for safety. A turbo charger raises the compression of the engine, so if you are already sitting at 10 or 10.5:1 ratio...a turbo could put you in the upper 11's:1 which could potentially damage the engine if its not built for a ratio that high. Lower your compression to 9:1 and you'll avoid any danger of high compression.