Cam
GAZ
mentioned that marine engines have different cams. How and why are the cams
different? What are the effects on RPM? etc
Thanx
Gordon
Brian
at different RPMs and to produce different amounts of torque/horsepower or
different torque/horsepower profiles. My Chevy V-8 truck motor is always
turning between 1000 and 2500 rpm in 99% of my driving conditions, but a
Chevy V-8 for a boat has to run from about 600 to 5000 rpm and develop a
heckuva lot of torque in the low end.
Personally, I can't see spending a lot of money in marinizing a car motor.
Car motors have far lighter loads on them and the main bearings (etc) are
designed for the car load. Driving a boat with a car motor is like driving
full throttle up a very steep hill...all the time. Marine motors have more
and bigger mains for a reason. A marinized car motor will not last nearly
as long...unless in a slower displacement hull that does not put excessive
loads on the motor.
Brian
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"GAZ" <zum...@tscnet.com> wrote in message
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Larry
I got this one.
Marine engines are always "running up hill" compared to auto/truck motors.
To take the truck down the road you step on the gas (engine under load),
then it "coasts" or runs with a light load. Cams in this application need a
wide power band.
Boats on the other hand, are ALWAYS running under load and quite often are
running at a heavy load, at a constant RPM for very long periods of time.
Cams in this application need to produce good power under constant load.
Hope this helps :-)
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Larry
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"GAZ" <zum...@tscnet.com> wrote in message
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Carron
engines are mush tougher than car engines. If we were talking about the rock
crushers of the 20s, that would be correct, but since the 30s, most civilian
marine engines have been nothing more than auto engines with some minor
(thought important) mods. The bearing area on a modern (1960s) V8 is way
sufficient, considering the better metallurgy post-war compared to the rock
crusher era.
All the famous Graymarine engines were from cars; of course Chrysler engines
were 318/361 CID car engines. The Hercules was similar to the 4 and 6 cyl
Continental side-valves. Buick engines were used pre-war for marine conversion.
A good many of the earlier Chris engines were designed by Chris as marine
engines, but were essentially auto engineering, and finally, the I/O drives
today are all automotive engines.
So, let's be honest and intelligent when discussing these issues. If you want
to convert a car engine to marine, start with a model that was common, say a
318 Chrysler. Add a marine tranny, an RV cam (backward if required),
non-ferrous gaskets and freeze plugs, a marine manifold, a cooling water lift
pump, marine manifolds, a carb wedge block, a spark arrestor, a marine starter
and alternator (don't want those nasty sparks flying about) and that's about
it. Oh, I forgot, stainless fasteners and an aluminum sump.
Note that you'll have spent a good deal more than buying and rebuilding a used
marine engine (conversion) if you do this. But, you'll have a "marine engine"
when you're done, just as Chrysler and Gray did :-)
Pat Ford has been very quiet on this topic; maybe he has worn himself out on
the subject. I'd like to hear his views.
Cheers/Carron
"LABOR SUGIT"
Larry
Don't forget to add the MARINE engine tag and adjust the price accordingly
:-)
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Larry
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"Carron" <step...@aol.comNOJNK> wrote in message
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GAZ
"Brian" <brianNS...@attbiNS.comNS> wrote in message
news:FA6o9.66325$DN4.9661@sccrnsc01...
> The cams are always going to be different when a motor is converted to run
> at different RPMs
What else is changed to change the rpm range to marine apps?
and to produce different amounts of torque/horsepower or
> different torque/horsepower profiles. My Chevy V-8 truck motor is always
> turning between 1000 and 2500 rpm in 99% of my driving conditions, but a
> Chevy V-8 for a boat has to run from about 600 to 5000 rpm and develop a
> heckuva lot of torque in the low end.
>
> Personally, I can't see spending a lot of money in marinizing a car motor.
> Car motors have far lighter loads on them and the main bearings (etc) are
> designed for the car load. Driving a boat with a car motor is like
driving
> full throttle up a very steep hill...all the time. Marine motors have
more
> and bigger mains for a reason. A marinized car motor will not last nearly
> as long...unless in a slower displacement hull that does not put excessive
> loads on the motor.
>
> Brian
The old Crusaders were all Chevy engines. The 6 cyl was the Chev truck
engine which had more mains. But I still want to know how they get more
RPMs. Is it cam only? Balance? ??
Gordon
John
Their are a few other things as well. Some engines use completely
differant heads. As an example, I know the old Ford 351's actually
used 305 heads on marine engines, it had to do with the torque curve
with these heads rather than with 351 heads. Rods are usually heavier
ones found in heavier applications, like tow truck engines or RV
engines. The same holds true for pistons, rings and valves. The sheet
metal is actually thicker on marine and the intake manifold is
frequently differant. The total extra cost, if you had to buy them,
like another $200.00, plus the gaskets, call it $300.00. I've used tow
truck cams on my boat, better torque curve than marine, they work
great. It's not a lot of extra money to the engine manufacturer, I bet
it's under $50.00 to them. On reverse rotation engines their's maybe
another $50.00 to the manufacturer, if that much.
Steve Lusardi
correct, but the truth of this matter is simple. It is called duty cycle. It
should be apparent to all that if the intended usage involves heavy loads
for extended periods, automobile engines are not suitable, period!
Automobile engines are purposely designed for light weight and intermittent
loads. As an example, a 350CID Chevy V8 can be Brake rated between 250 and
350 HP, but the very same engine is only SAE rated at 54 HP. The device that
is used to rate the engine is a dynometer and is the same for both cases.
The difference is only in the test. A Brake test is only run long enough to
get the maximum torque rating across the engines power band and them the
test is terminated. On the other hand, the SAE test measures total work
completed (without failure) over a long period of time. The design
differences are large. for instance the cooling system on an auto engine is
fed cold water to the front of the engine and hot water is returned from the
same side whereby the front cylinder is cooled more aggressively than the
rear cylinder. The typical industrial engine cylinders are fed from a cold
water plenum equally and the hot water is returned is the same manner with
the use of a common return. In many cases, the connecting rods have a
drilled passage for oil that is passed through the wrist pin and strayed
onto the bottom of the piston head for additional cooling. This, of course,
demands an oil cooler and much larger oil pump to handle the increased
volume demand. In addition, the auto engine is oil lubricated is series
where the rear main crank bearing receives maximum oil pressure and flow and
the front main receives very little of either. The industrial engine is
oiled in parallel like the cooling water. These design changes and others
obviously add reliability and cost. There is no free lunch. Please keep in
mind that on the water, there is no AAA and engine failure can be life
threatening as well as an unnecessary burden on our Coastguard. Please use
common sense. As to the original question, a cam change not only provides a
different powerband profile, but allows the engine to change rotation. Most
marine engines are left-hand and auto engines are right-hand. Please keep in
mind that the cam, distributor drive gear and starter need to be changed and
sometimes the oil pump, to convert rotation.
Steve
John
engine. In short, it dictates at what RPM's the engine develops peak
torque. In a car, you have a transmission with gears, so torque at low
RPM's isn't as importsant, so the torque of the engine is designed to
peak at hign RPM's, the gears take care of the low end. But a boat,
which is much heavier, and has no gears to chose from (except reverse)
must be able to produce lots of torque at low RPM's so it can get the
boat up on plane, which requires a lot of power. Once the boat is up
on plane the engine does not have to produce as much torque/power.
Their are non marine cam's that work quite well in boats, but their
heavy duty application cams used on tow truck's and RV's. But if you
do not have the ability to produce a torque curve, which takes in more
than just the cam, stick with the marine one.
Carron
Much that you say is true, but irrelevant.
Most "marine engines *are* auto engines modified for the intended use. So it is
plainly irrational to say that auto engines aren't suitable for marine use.
Please don't persist in this irrational view here. Take it to Mercruiser, OMC,
and Volvo, or go back to Gray, Chrysler, etc.; they might be interested in
hearing this "interesting" view :-)
I'll say it again, and you cannot refute the statement.
Marine engines *are* AUTO ENGINES!!!
Cheers/Carron
having owned a good number of these "marine engines"
"LABOR SUGIT"
Ron Thornton
not to expect the same performance in a boat from my newly rebuilt Ford
460 vehicle carburetor as from a "marine" carb. He said the power
circuit (main jets I think) is different to accommodate the different
power curve in the marine engine. Presumably this is mostly due to a
"marine" cam.
There goes my dream of dropping the 460 into that 14' frp hull I've been
saving. Oh well, back to the '65 Mustang.
Southeastern Virginia, home of PETA
"People Eating Tasty Animals"
Rick Tyler
wrote:
>I have read most of the responders to this query and most are partly
>correct, but the truth of this matter is simple. It is called duty cycle. It
>should be apparent to all that if the intended usage involves heavy loads
>for extended periods, automobile engines are not suitable, period!
>Automobile engines are purposely designed for light weight and intermittent
>loads. As an example, a 350CID Chevy V8 can be Brake rated between 250 and
>350 HP, but the very same engine is only SAE rated at 54 HP.
I believe you are confusing some issues here. All automotive engines
sold in the US now are rated according to SAE net horsepower. A
350CID (or, more commonly now, 5.7 liters) rated at 300 hp will have
tested that using an SAE test. "SAE" is an abbreviation for "Society
of Automotive Engineers" by the way, for those unfamiliar with the
term. As for 54 HP, I do not know what test that might be, but I can
envision it being some other SAE test with which I am unfamiliar. By
the way, even low-specific-output marine diesels typical put out at
least .25HP per cubic inch. While I cannot argue with your 54HP
figure, it seems very low, no matter how you measure it. Can you let
us know where this comes from?
> The device that
>is used to rate the engine is a dynometer and is the same for both cases.
>The difference is only in the test. A Brake test is only run long enough to
>get the maximum torque rating across the engines power band and them the
>test is terminated. On the other hand, the SAE test measures total work
>completed (without failure) over a long period of time. The design
>differences are large.
<snip engine design differences discussion>
You can cross oceans in 45' motor yachts with a D/L of 300 or more
using diesel engines of only 150 continuous HP or so. These engines
look like the ones Steve describes -- and they tend to be big in cubic
inches, tend to be heavy, and have low power-to-weight ratios. Most
coastal motorboats just don't need these sorts of engines, and, in
many cases, would make their owners unhappy. They do not want to run
to Europe at 7.5 knots, they want to dash to the next island at 35
knots. They need low weight, and high horsepower at high RPMs. These
requirements are inconsistent with long-life and long duty cycles.
They do, however, resemble high-quality automotive engines.
I am not suggesting that auto engines make good choices for boats. I
am just suggesting that for a lot of boats, auto engines and marine
engines are pretty similar, and that all of these engines are *really*
different from those found in real ocean-crossers, working boats,
commercial fishing boats, and tugs. I do not think we should confuse
ocean crossing passagemakers that need weeks of continuous-use
reliability with the vast majority of motorboats that never run more
than a few hours at a time.
Rick "Not a marine engine engineer" Tyler