usafhg wrote:
This is in response to a thread that was discussing the limits of
naturally aspirated HP in a 305 c.i.d. engine.

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. As far as reliable operation is concerned, lets
look a moment (bear with me) at the Infiniti G35 VQ 3.5 liter 6
cylinder engine. Normally aspirated, it puts out 300 HP (up from 260).
And it has been rated one of the top engines in a car under 50K for
about 10 years. Now I realize it isn't apples to apples. The air
intake might be more restricted in the boat engine without a fair about
of help--I don't know. But the point is today's engines are more
advanced, without the bolt-on technology enhancements.

Just to get a sense of what's possible by comparison, the Nissan
Skyline GT-R 2.6 liter inline 6 cylinder (RB26DETT) with twin turbos
has been modified over and over again to 600HP+ with just bolt-ons and
a new engine management computer as a start. Some have modified them
to greater than 1000HP. That's not naturally aspirated, but that's
also a 2.6 - 2.8 liter engine at over 1000HP without NOS! Incredible.

Look at the Suzuki Hayabusa. 1.3 liter inline 4 cylinder motorcycle
engine running about 170 HP stock. Mods take it over 200 easy, still
naturally aspirated. And turbo Busa's run upwards of 400HP+ without
NOS--certainly pricier.

Now, there are design limitations to some engines, but the naturally
aspirated 305 is capable of more than 260 HP. Using that engine block
with modern components and design tweaks, it would seem that much more
can be achieved. If not, use a different engine. Unfortunately, I
don't have specific 305 examples on the top of my mind, and I'm not
sure what some might call reliable performance either.

However, take this additional example from the 2007 SALEEN S281 3V
Coupe Mustang, which is a high quality built engine by Saleen. Running
it moderately most of the time and hot sometimes with proper
maintenance, this thing wouldn't quit on you for a couple decades or
so...

ENGINE
Type 4.6L, 3V, SOHC V-8
Bore and Stroke 3.55 x 3.54 in.
Displacement 4.6 liters, 281 cu in.
Accessory Pulleys Saleen Underdrive Pulleys
Exhaust System Saleen Stainless, 2.5 in. Variable Exhaust
Horsepower 335 bhp @ 5200 RPM
Torque 345 lb-ft @ 4500 RPM
Fuel Premium Unleaded 91 Octane
Intake Saleen Design Hi-Flow Inlet Tube and Air Box

Granted, Saleen's Hi-Flow Inlet Tube helps air intake, and a front
engine design puts the intake in position to swallow a lot of air, but
this is still the naturally aspirated version of this engine, which is
smaller than the 305 by 24 cubic inches. And one thing I don't see
limitations on in a boat engine is exhaust. It seems that should be an
advantage from a design potential standpoint. Not sure what emissions
regs there are, but I would be surprised if it is more than cars in the
state of California. Haven't heard any push for hybrid boat engines
for example.

By the way, this upfit mustang costs around 44K retail, which includes
ALL of Saleen's adders. The engine itself, without the highly touted
Saleen Supercharger, isn't that particularly expensive, which means it
isn't simply a case of throwing money at overengineering like a Porche
or Ferrari or something. It is powerful, practical, naturally
aspirated and reliable--which are all criteria of this topic. And I'm
not saying boats need this engine. I'm saying the same concept can be
applied to many engines.

Of course, this is a high volume engine (in its original configuration
from Ford) which helps the base price of each. A specialty engine
would have to cost more to deliver the same result when looking at
amortization differences (total cost & profit / num of builds).

First you need to know a few things about new vs old engines and boat
engines. Most boat gas engines are based on older designs for a few
reasons. First, older automotive engines are long stroke engines, they
produced good power over their RPM range, especially at low RPM's, but
they have a limited range of RPM's. Most new automotive engines are
short stroke engines, they produce limited amounts of low end power,
they produce most of their power higher up in the RPM range, they also
rev much higher. Now on a boat, you need low end power, to get up on
plane, a short stroke engine just doesn't do that very well, they tend
to have very short lives as a result. Older engines tend to be made of
Iron, newer automotive engines are made of aluminum. Overheating on
boats is all too common because marine cooling systems are easily
clogged or restricted. Overheat an iron block engine and, as long as
you don't let it go too far, you'll probably get away with simply
clearing the blockage and going on your way. Overheat an aluminum block
engine, even minor overheating, can seriously damage the engine,
aluminum tends to warp when overheated, their just not as forgiving. I
have little doubt that your Infinity engine would have a brief, and
troubled, life, in this application. Most of the other engines you
spoke about have very limited lives even in automotive applications.
It's one of the reasons you see mostly older American designed iron
blocks being used every where in marine gas applications. The only non
American made block I know of that is common is the four cylinder
Volvo, and I beleave it's iron and a long stroke engine. Several years
ago BMW entered the stern drive market, they lasted about one season,
and you would be very hard pressed to find one still running.