The benefit you're getting is from closing the inlet valve earlier, more than opening it. I don't know how much overlap there is on the standard camshaft timing, but by advancing the inlet cam you're increasing that overlap which may help claw back a little of the high rpm torque you'll lose from closing the valve early, but overall your peak power figure will have dropped a little. Similarly you supercharged owners could potentially gain a little from retarding the inlet cam or advancing the exhaust cam slightly so you're not blowing all that nice charged air straight down the exhaust port.

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Ph1 306 GTi 6 | RX8 231 S1 | YBR 125 Cafe Racer | MT-03 660