That is a good point as well. In a typical boat the power curve has to
deliver at a lower rpm. Otherwise the boat is a dog out of the hole.
Becasue as he points out boats are "one-speed" drive trains. A lot of
car engines make hp with rpm and the opportunity to do that is more
limited in a boat. That can be solved with a transmission but that
adds to the cost.

A number of the later model gm v8's in cars are able to run higher
compressions because they reversed the cooling flow. Sending the
cooler water to the heads first lowers the risk of detonation. But
that can only be done in a boat with a closed cooling system. Again
raising the cost.

Boat engines have mostly relied on more displacement to get more hp.
It's cheaper and more reliable that pushing the limits of smaller
displacement engines to get more power. As boats get larger the
percentage of the boat weight that is engine weight is less than a car
so the extra weight in a larger displacement engine is not as much of
an issue either. Also unlike cars the engine weight is not as much of
a consideration in handling. A 25 ft boat with a gm tall block (502)
will operate pretty much identically to a 25 ft boat with a 305.
Except the tall block version will be a lot faster. So why push the
305? Once you add the performance enhancements it will end up costing
as much as the tall block anyway. Over the long haul the vanilla tall
block will last much long than the souped up 305.

Short Wave Sportfishing wrote:
On 2 Oct 2006 13:55:17 -0700, "usafhg"
wrote:

Well, first, I must confess I don't know too much about recreational
boating engines specifically. However, there is much in common between
car and boat engines.

I've been watching this thread and found it very interesting.

However, I think I've got to chime in here.

In a general sense, yes, there is a commonality between car and
inboard marine engines.

Specifically, they are two different animals entirely.

I can't remember who, but somebody made the point that marine engines
are designed to run full bore all the time which is a high stress
load. High performance car engines (retail, not race) are not
designed to handle the same stresses for long periods.

The main reason is gearing. Marine engines are generally direct drive
through a drive train with no external transfer of energy by changing
gear ratios. Automotive engines don't develop their horsepower in the
same power band as marine engines and use different ratio gears to
provide mechanical advantage.

I'm sure one can take the 305 and bump the power - we've done it here
at the house with my oldest son's '92 Camaro RS audio/visual
masterpiece show car - it's not hard to bump the horsepower.

It's how the horsepower is applied that makes the different. It's
more a question of now that I have the horsepower, what the hell do I
do with it with marine engines.

In the case of a boat, you are dealing with a prop rather than a drive
train with variable or changeable gearing. Applying the power is an
entirely different set of challenges.