I posted a thread a while back about my engine/boat not performing and I have fixed some things since but no change. I have a 28' Saber Offshore, which most of you know by now, with a carburated, new 950 cfm Holly, 502 with hi-rise dart intake and IMCO manifolds & exhaust. All I know internally is it has iron heads and maybe a mild cam, but not sure which one. Engine was just freshened up by More Power marine in Grand Rapids, MI and they put new rings and bearings, ported and polished internal parts and reassembled. I have a Bravo one drive with a 25 pitch Mirage three blade, do not know if prop has been labbed or stock. Anyways, I assume I have around 415-450 HP by my setup, does that sound about right as far as guesses go? Engine runs strong but drops off at 4600, it's like that's all it's got but only hitting 56/57mph and 4800 after drive is regularly trimmed and tabs all the way up . I believe the boat weighs around 5600/5700lbs dry. Shouldn't I be running in the mid 60's and hitting 5200-5300 rpm WOT? Sorry to write so much, just wanted to let you know what I know about boat. Any Help???

Have you changed props?

WOT RPM will be determined by propellor selection as much as anything else.

Not knowing the boat, or the hp level, or the bottom condition (of the boat), it could be just a 57 mph boat, or it could run 65. I have a 27 fountain with a single 502, stock though. I've gotten just over 60 out of it, and i'm still playing with prop selection.

Did you check the timing? Folks generally recommend 30-32 degrees total on a stock motor. with cam and whatever, i don't know what to recommend for your motor, but when i bumped my timing up from 28 to about 31 last year i picked up about 2 mph.

If I was to make a I was guess, and only a guess. I would say you are over carberated. The carb your running will give you huge volume, but very little air velocity. If your cam is mild and your heads are stock square port your carb is way to big. I would think an 800 Holly would be as big as you would want to go depending on how much power your putting out. I would check with one engine builders (Tyler Crockette, Bob Teague) and see what they think.

In my meaningless opion, you have a lot of prop slip if you are turning a 25P at 4800 and getting only 57MPH. Something is wrong. Try to confirm those numbers and check with Saber Boats and also the prop experts on this board like Throttle Up and BBlades. If it is a 25P I am assuming it is a Mirage or Mirage Plus. You may want to go to a 24P Bravo.

Also, that carb is too large for a 502 turning in the 5000 RPM range. I don't know if it is hurting anything other than throttle response and idle quality. I think 32degrees total advance is a little conservative. I would bump it up to 34-35 degrees.

I would start by confirming that your speeds and RPM are accurate so you have some good data to work with. If those figures are correct, you have to get that prop slip down.

I'm no expert, but my first thought was the carb also. I have a mild 540 and it's running an Holley 850 CFM in the same targeted 5000-5300 RPM range as you. Same GM iron heads and a mild cam.

I'd suspect our boats are about the same weight, al beit very different hull's, mine is a bathtub, and I turn 5100-5200 RPM and in the 65 MPH range. The motor makes something in the 575 HP range by calulations and experience (not mine ).

Sometimes bigger really isn't better.

From my experiences, in a car, if you are running too large of a carb, it will do just what he is describing. Yes, he will also need to test some props. I have a lighter boat and a 454 Mag and turn a 24" Bravo1 4900rpm at 66mph on GPS. This is the prop I would try on his setup, although if he is making power to 5300rpm he may need to run a 22".

What is your rev limiter set at?

I am no expert at all when it comes to carbs or props. The setup that I have is the way that I purchased boat. The engine builder, More Power, was the one who put the new 950cfm Holly on it. I assume that they knew more than me about performance engines since that is what they do and I figured that they installed that carb instead of a 850 for a reason, maybe not. It does seem that the carb is a little big for what I have seen, based on what other people have told me. I did try a 23 pitch Mirge 3 blade and I turned 5200 or so RPM but only hit 53/54mph gps, by the way the speeds I am quoting are all from gps.

Other people I have talked to with the same Saber Offshore with 502ci are running in the mid 60's so with the same weight, hull, and for the most part, power are running much more efficiently than I am. I really appreciate all the input and keep it coming...

Why not go to More Power, or who ever built the engine and see if you can get the specifications for the cam they installed.
Then get with one of the valve train experts here on OSO and they can determine where you should be making power, and what to expect with your combo. See if you can get compression ratio also.

They put the 900-950 carb on your engine because that is what they had sitting around. It is that simple, it is not because you need it. However my main concern would be why all the prop slip. Changing the carb is not going to effect prop slip. You speeds are not propotional with your prop. Are you running a 1.5:1 outdrive? That is important too.

I agree with being overcarbed. I think an 850 would be better.

Also, I think you're overpropped. I had a 22 Avanti (basicly a 24 pantera with 2 ft. chopped off the transom) It was heavy for it's size but with a 450hp 454 I ran a 23 Mirage 3 blade about 4800 until I kicked a rod. New motor was a 498, 850 Holley, that made an estimated 550-570ish hp. With the same prop it pulled like something scary to 54-5500 and had plenty more but I only went boating in the Pacific ocean so I never really got a chance to hang it out but my engine builder recomended a 6000 rpm rev limiter.

With the first motor the speedo said 70 but it was not GPS so take it for what its worth.

With the new motor it would peg the speedo at 75 and keep pulling but in that little boat in the Pacific, the last thing you wanted to do was look at the speedo.

Hope this gives you some prop ideas

Yes, my drive is 1.5:1 and I called More Power and they reinstalled whatever cam was in it. What happened was This guy scammed his insurance company but parking his boat, over the weekend, at a consignment lot and when the broker got there Monday he lifted the engine hatch and found the carb, dist, and intake missing and figured some stole it. So they pulled the motor and sent ti to More Power to go through it in case a bolt dropped into crankcase. They just port/polished block, magnufluxed heads and milled, ground valves, deglazed cylinders, installed new main & rod brgs, piston rings, cam bearings, intake, MSD Dist, and carb, ect.

They did not replace cam and when I called to see what it was they were not what cam was in engine from when they did repair. So, how do I figure what cam I have without pulling it??
THANKS Whiteknuckle