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Aq 225d/ 280

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signusx1

Contributing Member
My 5L engine has run its course and I am now in a position to repower. What is the maximum horsepower a 280 outdrive will handle?
 
The older 250s were (according to two different factory reps) capable of bursts of up to 200% of that rating.
Not too much has changed with the 280.

You could safely repower with a 5.7L or a mild 383 with no issues other than installing new main drive gear bearings if this drive has some hours on it!

As for over-all performance, you'd do as well, or better, with a 5.7L and the addition of the Duo Prop lower unit.

If custom building one, you have a prime oportunity to get away from dished pitons.... but that's another story!
Later engine blocks may not be fully machined for a mechanical fuel pump.


Which ever way you go (later model engine, for example) you must maintain the 153 tooth flywheel.

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400 = Siamese Cylinder walls.... not a good choice for marine.
Build a 350, 377 or a 383 instead.

Or......... save yourself the trouble.... do a 5.7L and install a Duo Prop.
The 5.7L w/ a Duo Prop will do more for your boat than a 377/400 will do with a single prop drive!
 
Over the years I've put lot's of BBC in front of 280's. If you know what parts to change over and what kind of shimming to do there is no problem. Lot's of small tricks to make them live with 500-700 HP. Many years ago our shop took care of two offshore cig boats, both with BBC and hardly ever had a problem with the drives. Keeping the engine affixed between the stringers was the problem.
 
Ricardo, I am planning to build a 4-bolt main 350 ci SBC using a 400 ci crank.
Can you steer me in the right direction for a cam, heads and pistons?
 
Well, I can steer you in a direction that would work for me..... but the choice will be yours.
Let me post a few links for you later. I'll have to dig them up.

Lots of ways to do it wrong, one being the use of the full dished piston, IMO.
The automotive guys seem to be OK with a full dished piston!
They even use the longer connecting rods......, but this makes for a short piston skirt.
Since this will be a Marine SBC, you'll want to steer clear of many automotive type suggestions... and this would include the longer rods!

Several ways of building one correctly, using a Q/E (quench effect) piston that offers the correct C/R for your cylinder head choice.
A good Q/E, or "Squish" style piston/head combo, helps us combate Detonation...... and this is important for a properly built Marine SBC, since detonation is a rather large potential in a Marine SBC.
The full dished pistons can not offer a Q/E..... and in fact, can add to the potential!
A good Q/E piston will cost you a bit more, but should not break the bank.

What are your plans for cylinder head choice at this time?
The combustion chamber size will affect which piston volume you will select.
There is a certain Q/E piston that compliments the shape of the Vortec chamber.
There is another style Q/E piston that compliments the older D shape wedge chamber as well.

Lots of choices to make..... and the better educated you are, the better this new engine will perform and last, IMO.

Have you considered what the Duo Prop will do for performance?
 
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Oooooooew booooy! I'd have to start with the size of the hull, what you expect from it, and what your budget is. It would be fun to spend YOUR money! Har Har!

If you were to stay with an early casting, you may be able to use your existing intake system. Keep in mind that some of the lighter castings are not suitable for marine use.
(see Dennis Moore's "SBC Marine Performance" for some great info)

If you were to go with the Vortec heads, your intake manifold now changes.

In any event, you MUST select pistons and cylinder heads simultaneously, since each selection affects the other!
A good Q/E piston for an early 76cc cylinder head will not work with the 64cc Vortec cylinder head.... for example!
The end result C/R, and the Q area of the piston will be different for these two cylinder heads.

I rarely recommend a camshaft for anyone!
For this, you're better off to speak with an expert at one of the many companies that specialize in this. That is what I would be doing!
Comp Cams, for example.
Make sure that they understand that this is a Marine application, and that you intend to build a 383 version.
This person may also want to know which pistons/heads you are considering!

You may also want to consider a later block, and go with roller cam followers.

Lots of decisions ahead of you! :)
 
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