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

Downtown42

You're in the wrong forum. Try the SuperBoat forum.

Superbabi

Come on down to the Superboat Fourms, the guys will give you all the answers you need.

Superbabi

T-400, I'm surprised at your top speed, seems like you should be getting well over 80 mph with 900 hp, perhaps some of the Superboat Guru's will get you some info.

z.zuperboat

5100rpm with 23p and a 1.5 gear = 68mph correct ? Thats giving you 8% prop slip. Thats a great number. My conclusion is the motors arent making the power you think. More like 300hp then 400hp. Start to fall off over 4000rpm NO GOOD. Timing total at 28 try uping to 32-34 I bet you see 70mph.

Pat McPherson

Hi T400s,
You have a vary unique boat for sure. Most 30' Supers from years back had outboard power. She's a 1982 with Bravo drives; did she originally have TRS or Alphas?
I'd have to agree with Superbabi and Zuperboat, with 800-900HP, you should be going a lot faster.
The only boat we've talked about here on OSO that would be similar to yours is a Y2K with twin 320HP Merc 6.2L Bravo drives. That boat reportedly runs over 80mph.
These 400s you have, were they built for marine use with a nice flat torque curve? Like you and Zup said a bit more timing may help. I ran 32-34 total in my old 280TRS engines.
When you say the power starts to drop of at 4000rpm, I'm assuming you mean the torque? You want to prop for 1400 to 1500rpm above peek torque or about 100rpm above peek HP.
Mirage or Mirage plus props are a good choice IMO. You may want to try changing the rotation; if you're spinning out, try spinning in. Spinning out the boat will likely handle better, but in may give you more speed. Merc also has a 4blade round ear, the revolution 4. You could try a set of 21p; BBlades here on OSO has a cheep test program.
Post some pictures please; we'd love to see her...

FX10

I ran this by Coen yesturday. He says there's definately something wrong. He says that hull, with that powetr should do around 80. Also consider X dimension. 25 years ago, the X was lower by around an inch or 2.

lightspeed

RC Marine 30 Had Twin 355 CI , TRS Drives ,MCM Trans ,Motors Making 425 Hp And That Boat Ran In The 80s Any Day Of The Week ..Sounds Like Your Motors Are Not Making The Power You Think. Even If The X Was Low The Boat Still Should Run In The mid to High 70s ..The TRS And Trans Robbed some Power The Bravos Only A Little Check Your Motors After You Put The Cams In. Have Your Motor Put On Richie Zuls Dyno This Way You Have An Exact # And Can Go From There .I Also Think RC Used 23 Or 25 Mirages As Far As Tow In Just Tow Them In 1/8 To 1/4 ,,,,,Thats A Try It And Run It Deal Every Boat Is Different

z.zuperboat

RC marine was raced years ago and back then I think either you ran a mirage or a cleaver. Not as many choices as today. Bravo props would probably be an all around better prop. Anyway lightspeed is rite Zul has the most accurate dyno around.

z.zuperboat

Does this boat really exist ? I thought between everybody here we knew most of the boats out their. Where did this one come from ?