Boost is measured pre-throttle on ISO so with wheel spin, shift spikes, etc, it's not uncommon to see 18-19psi on E85 mixtures. If you are seeing that on pump gas though you definitely have an issue. The safest thing though is always to do a log and send it in if you need specific tuning advice.
MARCH MADNESS - CLICK HERE For ALL CRAZY SALES
N54 Catless Downpipes - 329.00 Shipped!! ar design downpipes 15% OFF (including Free Ship) Evolution Racewerks FMIC, DP and Oil Coolers @ 15% OFF + FREE SHIP - WAGNER FMIC and DOWNPIPES - PM FOR INFO!