T400's

Hello everyone, and especially you Long Island Sound Superboat owners/enthusiasts.
I have a 1982 Superboat that is rigged with 400 cube small blocks and Bravo 1.5's. The boat is a pleasure to drive and handles really big waves at amazing speed and flies very well balanced. I had a 35 cigarette and in some conditons it seems faster, getting "light" much more easily. That aside, I am trying to tune the boat for the best top speed I can. I have rev limiters set in the six area, open exaust, and well built engines. They dynoed in the 420 ftlb area last year and this year I am putting in roller cams for a few more HP. I have run three types of props over the years, 23p three blade cleavers, 23p four blade hydromotives (borrowed off the cigarette) and now I use 23p mirage pluses. I think I should be in the 70's with almost 900 HP out back but am stuck in the high 60's. I use what feels like a healthy amount of trim, (almost 50% on the gauge) and the bow runs with excellent lift in smooth water. In a chop the boat runs flatter with less trim and you can feel all the air going under as it skates along, with a bit of chine walk but never scary. Its a very exhilarating ride and loves to get airborne and comes down like a feather almost any which way you land, not like some of the bone-jarring landings in the cigarette that make you feel like you broke the boat maybe. I have done some absolutely nuts rides and am always amazed how tough it is.
From what I can tell the props are running right on the surface and don't aearate unless I use almost 50% trim on the gauge. When setting the boat up, we positioned the engines so that they would fit under the hatch to keep a clean look and for the occasional tanning session, etc, which just happened to be the factory recommended 14" X dimension. Its a tight fit back there, both X and Y.
I have seen the debate over singles and twins for the 30' Fountain. The Superboat beam is only 6.5 feet. It sure is a great handler but I would like to see almost 80 if I could. At 5100 RPM the Mirages feel like just a bit too much prop, as at that speed, 68 or so, the boat finally feels like its getting up on the keel and passing a nice air cushion underneath. The Hydromotives were very efficient out of the hole, obviously, but felt like a brick wall at 4800-5000, and slightly less speed. The cleavers spun up to 6000 but I was too busy driving back then to see a gps. The speedmeter is useless as all it does is get air into it and never goes above 50 or so.
The engines power curve declines slightly from 4000 up. The boat planes at only 2600RPM!
There is absolutey nothing on board or up front, its really light. I should be able to run a bit more timing advance, I think it was set up for 28 total degrees. Hard to imagine the engines being overworked.
So I would appreciate any suggestions to get me out of the 60's. My guess is with the extra weight in the back, the boat is pushing too much on the keel, so a prop that lightens the stern might be the answer?? What about the amount of toe/in or out on the bravos? Anyone that could guesstimate the optimum settings overall?....
thx

PatriYacht

How much hp do they make and at what rpm? What rpm was peak torque at?

T400's

between 3600-5200 rpm the torque number is over 400 with the peak at 4200, 425 ftlbs. HP peaks at 5400, at 403 HP. The roller cam I am installing is a bit peakier, but I won't have them dynoed. From what I have heard the roller cams are good for another 20-30 HP.
thx

Dave M

Hey T400's,

Sounds like a cool boat. Is it the "RC Marine" boat? Post this in the Superboat section. Somebody will be able to help. I have a 24 Super.

PatriYacht

It sounds like you can use more rpm's, even more with a new cam. Mirages seem like the fastest prop on 30' fast boats. Try a pair of 21's. They're all over E-bay cheap.

AIR TIME

THAT CAUGHT FIRE THE YELLOW ONE WITH TWINS

AIR TIME

With 800hp that boat should scream, somethings not right, mine makes peak tq at 4800, hp at 6000, maybe your tq falls off to quick.

Pat McPherson

For sure...
I'd expect with that kind of power she'd run 75-80mph.

I honestly don't think your engines are making anywhere near 400HP in the boat.
What type of exhaust are you running?
If you tuned on the dyno with headers, maybe she's too fat. Like we said over on Superboat, more timing, 32° total, should help.
With the new cams, more advance, and prop'd for 5500rpm, your going to see more speed no doubt...

cigarette28ss

Isn't the 28 degrees total timing he is running a little light?

AIR TIME

on my big 509 on the dyno I think it was set at 37*degrees does that sound high