Watch your valve train like a hawk! Mercury never intended these engines to run 6,000 rpm. If they're stock 600SCi heads, they were rated at 5,200 max. At 6,000 you will frequently replace rockers, springs and valves -- if you are lucky. Pistons, rods, cranks and cylinder blocks are likely, if your engine swallows a valve.

http://mercuryracing.com/sterndrives/hp600sci/specs.php

Your HP divides by 12 will give you a good estimate. 750hp/12=62.5 gallons per hour at WOT. That is per engine.

I have a single 600 sci stage 2 whipple. I am very happy with it and have had it for two years. I guess I should say happy except for fuel consumption. I don't have a formula but here is a good one. Keep your wallet handy!

VERY accurate, according to Smartcraft on my 600sci's with Whipple Stage 2 upgrades.

Have heard of issues spinning stock valvetrain too high, so re-geared to keep just above the stock 5400 limit. The last 25 or so hp achieved by the extra rpm is not worth the loss in reliability.

Rev limit is 5850, 400 more than stock. I'm not sure you have to watch it like a hawk, that seems a bit extreme. They should be inspected more regularly than stock, but by no means all the time.

Thanks Guys very Handy information...