Thread: 454 marine engine questions

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Hi, I just purchased a 26' boat with a BBC 454 marine engine. I noticed the previous owner has it set up with an auto Holley 750 double pumper, instead of the proper marine set up.

It is supposed to have 330 hp from factory. Since I have to change the carb, should I stick with Holley, what is easiest way to get more horse power from a marine engine?

I have above the water (thru-hull) exhaust, so I don't have to worry about a big cam causing water reversion.

Is there a specific cam, head, intake, carb set up that would get me close to 500 hp?

I'm guessing it is stock 454, except it has an aluminum intake, and MSD distributor and coil. I have no idea on what type of heads it has but the previous owner said it had the peanuts..THe boat originally had a 502 Chevy, but the previous owner blew that up and replaced with the cheaper 454. So now I'm looking for more power to push the beast along...

Thanks. Oh, I just ordered a 454 rebuild DVD from ebay since this is the first BBC I have owned. I have worked on some SBC 350's though, like changed heads etc.

Originally Posted by AdamB

Hi, I just purchased a 26' boat with a BBC 454 marine engine. I noticed the previous owner has it set up with an auto Holley 750 double pumper, instead of the proper marine set up.

It is supposed to have 330 hp from factory. Since I have to change the carb, should I stick with Holley, what is easiest way to get more horse power from a marine engine?

I have above the water (thru-hull) exhaust, so I don't have to worry about a big cam causing water reversion.

Is there a specific cam, head, intake, carb set up that would get me close to 500 hp?

I'm guessing it is stock 454, except it has an aluminum intake, and MSD distributor and coil. I have no idea on what type of heads it has but the previous owner said it had the peanuts..THe boat originally had a 502 Chevy, but the previous owner blew that up and replaced with the cheaper 454. So now I'm looking for more power to push the beast along...

Thanks. Oh, I just ordered a 454 rebuild DVD from ebay since this is the first BBC I have owned. I have worked on some SBC 350's though, like changed heads etc.

Like you said basicly use a marine approved carb.
Since you already have the 454 block I would at least up the cubes by making it a 496 with a crank change.
There is nothing I hate more than the "running valves" on a boat engine.
I would run a hyd. roller cam.
Another area that is often over looked is the exhaust valves in a marine engine.
I will not build an engine for marine applications un-less it has Inconel extreme duty exhaust valves.
The bad news is you will spend $300-$350 on the exhaust side.
What is your budget for this engine build?

Well my budget for this boat basically depends on what I get for my other boat (21' Wellcraft cuddy) that I am selling. It has a rebuilt 350 (40 over) with Dart Iron Eagle heads with SS valves. I converted it from the carb to a MPFI system and am guessing it has around 300+- hp now. Once I sell that in the spring, that'll be my spending money for this boat.

On the new boat, I doubt I will spend the money for the mpfi system, although nice didn't do much performance wise. I'd rather just spend the money on motor... but a marine carb is definitely a must. I don't know if I want a Holley double pumper or eldelbrock or? What works best with 454?

If I stroke it to the 496, should I run at least a 850 cfm carb? Also, marine cams tend to be very mild because of the exhaust exitting in the water. My new boat exits thru stern so camming is not out of the question. Would still need a torque cam that would probably run to about mid 5500 rpms.

Oh, being a used motor, I am seriously thinking about just pulling the 454 in the spring (or whenever I free up garage space to store motor) and going through it anyway just to be safe. Little things like compression test etc I can do in boat, but I would probably pull it to change heads and cam.

To answer you above question about $$, I am not opposed to spending money, or I wouldn't have a boat LOL

What do yo mean by "running valves" Never heard that term. Also, I know it seems early to be planning this if I don't intend to do much until spring, but I never like to jus rush into anything. Just basically trying to get ideas. Thanks

cam s in boats have to have a low speed idly so you can get them in and out of gear at a low idle. the cam needs to pull hard so you need TQ. i would go with a copy of a HP merc roller cam .getting some weight of the transom would help like alum intake and heads and ss manifolds . the stern drive has to take the power if a alpha drive then forget it you will need a better drive

Originally Posted by AdamB

Oh, being a used motor, I am seriously thinking about just pulling the 454 in the spring (or whenever I free up garage space to store motor) and going through it anyway just to be safe. Little things like compression test etc I can do in boat, but I would probably pull it to change heads and cam.

To answer you above question about $$, I am not opposed to spending money, or I wouldn't have a boat LOL

What do yo mean by "running valves" Never heard that term. Also, I know it seems early to be planning this if I don't intend to do much until spring, but I never like to jus rush into anything. Just basically trying to get ideas. Thanks

Running the valves just means to set the valve lash.
If you are not opposed to spending money then I would build the 496 with a forged 4340 rotating assembly.
Forged flat top pistons.
A moderate hyd. roller cam.
Either a large oval port head or a smaller rec. port head.
Yes, on a 496 I would run the 850 carb.

well how hard do you want to run .lower power a cast crank will be ok i would run a set of forged pistons this really has to do with how much is some money to you a 496 would work good

It has a Bravo One outdrive, so power isn't a problem. It already had an aluminum intake manifold, but I'll have to check to make sure it is brass lined since it is raw water cooled and I run in Salt occassionally. Salt and aluminum don't like each other.

The 496 Stroker kit sounds like a winner. The Bravo has a better transmission than the alpha so hopefully the shifting won't be a problem.

It is supposed to warm up this weekend a little in PA so maybe I can pop off a valve cover and read the #'s on the head. Also, I looked for the casting numbers on the block but couldn't see any... I'll look again.

yes that salt water can rise hell i work on boats and bravo has a much better gear set they are not cut like the alpha had cut gears the bearings in the case is what went out most of the time on the alphas the case would not hole up to the side load .you can get the intake epoxy coated inside and out

Thanks, I had my intake powder coated on my SBC 350 marine engine. Don't know how well it's holding up, but it hasn't leaked yet. I'll look into the epoxy idea too.

What would be a fair price to pay for a machine shop to make my 454 into a 496? I would rather a machine shop install the crank and rods and pistons, I can take it from there...

I have to bore the 454 30 over right, or 60 over to make the 496 stroker? And, since this is a marine engine, I heard it is a tall deck whatever that means. I am new to BBC's.

Originally Posted by AdamB

I have to bore the 454 30 over right, or 60 over to make the 496 stroker? And, since this is a marine engine, I heard it is a tall deck whatever that means. I am new to BBC's.

To build the 489/496 you also have to add the 4.25 stroke crank.
The 489/496 is built using the low deck 454 block.
The low deck height is 9.80,the tall deck height is 10.20.

You'll make more horsepower putting a better set of heads on there and raising the compression ratio than you will with a stroker crank. 400-425 hp is reasonable to ask for with a change of heads and cam. You'll get better fuel economy if you pick the right cam.

So, since the marine engines are tall deck, what does that mean for the stroker combo? Can I get more stroke out of it?

Originally Posted by erik erikson

To build the 489/496 you also have to add the 4.25 stroke crank.
The 489/496 is built using the low deck 454 block.
The low deck height is 9.80,the tall deck height is 10.20.