MAX RPM's??

[FULL-THROTTLE]

I have a 1995 Hydrodyne Grand Sport, it has a ford 351 GT40 and I believe a 1:1 direct drive, what is the max WOT engine RPM? Presently it will scream past 5000 if I don't hold it back. My son is going to be using it and I am concerned about over revving it.

Thanks

12437

[cadunkle]

I believe the GT40 is 4800 RPM max. If you're turning 5000 or a few hundred more it'll probably be fine. We're talking intermittent WOT, not hold it there forever. Most marine engine max RPM ratings are where the engine runs out of breathe. Mild cams, small carbs, low RPM intakes, bad exhaust ports, restrictive exhaust manifolds, etc. just mena there's not much point to revving them high as the power rapidly drops off before the point where crank or rods would be stressed. If you're worried and it'll just keep revving to the moon (5500+ intermittent is where I'd be concerned about a 351w bottom end) then put a prop with a bit more pitch on there to bring max WOT RPM closer to 4800.

[haugy]

Mine goes to 11.

[SquamInboards]

It is 4800 max, it's on a sticker on the engine originally, although those stickers don't always last. It's supposed to be 3800 max sustained, 4800 "momentary", whatever that means. As Cadunkle said you could put a little steeper prop on there. But if you often run with lots of people or weight, you'll be happy to have a prop that over-revs slightly with only a little weight. I chose my prop to get the WOT RPM just shy of 4800 with just me in the boat, 1/2 tank of gas or so. That way if someone borrows the boat there's no way they're running over 4800, ever. And I can get the boat to plane off still with 11 people and 500lbs ballast, no problem.

[CornRickey]

Mine goes to 11.

yea but the gauge only says "10"

[FULL-THROTTLE]

Thanks guys I appreciate the help, i dont know where it will top out at I saw it screaming up to 5k and had to throttle it back, I am giong for a new prop to be sure it doesn't over-rev.

[haugy]

yea but the gauge only says "10"

No, no. See normal ones say 10, mine goes to 11. See that? It goes to 11!




Seriously though, just so you know. You want to keep it under 4800 rpm. But I will say, I've had my 351w up to 5200-5300 a few times and it doesn't phase it at all. 8)