Sledge Hammer

I have a 555 built by a reputable builder that dynoed out at 610 HP @ 5400 and 661 torque @ 4400. Carb is an 850 Holley DP with 84 jets all around and 6.5 power valves. The heads are iron Merlin with 310 intake square port. Timing is set at 33 degrees. I hear people on the board running 34 to 37. Should I bump it up? How can you tell if you have gone to far since you can't hear spark knock in a boat? I have also seen comments about changing the fuel pump to aftermarket, removing the check valve from the tank, and modifying the pick up. Do I need to do this? The engine seems to be running fine, but if there are a couple of MPH left I woud like to get them. Currently running 85-86 on a handheld GPS since the one in the boat took a crap.

hoozeyurdaddy

when your engine was dyno'd, they should have tried it with more and less timing, thats propably where they feel good about it not detonating, call them and ask if it could go up a little, as far as the full sys., buy the keith eikart pump upgrade, it will boost the fuel sys. to 120gph, that should be fine for your application.

Ghostrider

If you're running anywhere near 600hp but you haven't gone throught your system from tank to carb, now's a good time. The stock fuel pump can't flow for 600hp so I'm guessing your builder upgraded yours. If it's still a mech pump, as long as it's a high perf upgraded one, it should do. Check your fuel line size from tank through filter / seperator, through pump and to carb. I run AN-10 the whole way just to be safe. The valve / tap / elbow on the vast majority of stock tanks is tiny. Mine was about AN-6! I junked the tap ( I added a bigger one later), and put a larger elbow in. There's a USCG mandated check valve too. I'm in Australia so I forgot to put mine back in. Make sure you run a small inline filter (10-100 microns) after the pump before the carb too, in case the pump goes.

Good Luck!