Have you got boost pressure gauges fitted? if yes then try to get them as even as possible, if not I would suggest you get some fitted as they will allow to balance the power output of the engines far more accurately than the rev counters, on most twin engine set ups neither engine will hit max revs when running alone as the props are built to be running together and both engines producing equal power. Talk to Paul Williams at Clements Marine 01234 378814. or sales@clementsmarine.co.uk. I have no connection with this firm but I have complete trust in them