The average individual that would have owned
a performance car in the 1960s, and the baby boomers that did,
in many cases no longer have a modern affordable toy they can
tweak to their own satisfaction. Serious performance today is
often available to only a few with large checking accounts or
extra good credit, and even for those that can afford it, the
high tech "compucar" is beyond the ability of many when
it comes to performance enhancements.
Computer controlled everything, intertwined
like a grapevine, often makes it difficult for all but the most
dedicated gear heads to make modifications that suit personal
tastes. Enter the family boat. Unencumbered with emissions hardware,
unreal paint and graphics, chrome, open exhausts, dual fours,
blowers, any modifications you can imagine, lots of tan bodies,
and all legal. The simplicity of the marine market stands in stark
contrast to the emission-restricted performance street vehicles
Most importantly for machine shops and engine
rebuilders, a major part of the marine market uses automotive-based
engines. The growing interest in rebuilt marine engines, both
standard and high performance, has expanded the need for machine
shops and production engine remanufacturers (PERs) serving this
market. It’s a market that includes engines ranging from production
remans to super exotic, i.e., cost as much as a house, to 1,000
hp-plus monster motors.
Based on information provided by aftermarket
gasket suppliers, marine engine OEMs and others already supplying
this market, it is estimated that the total demand for replacement
marine engines represents more than 20,000 units annually. The
two largest areas of this market demand involve engines that weren’t
winterized properly where the blocks, heads and manifolds suffered
freeze cracks (many first time boat owners are under the impression
that when the boat’s out of the water, the water is out of the
engine); and engines run in salt water that over five to 10 years
have rusted from the inside out.
In either case, the cores are often not rebuildable
and you have to include a core in the price of your rebuilt engine.
Surprisingly, only a small percentage of the engines replaced
every year are actually worn out from use. In boating, 100 hours
a year is a lot of use. Compared to a car operating at 60 mph,
that would equate to only about 6,000 miles on the engine.
When you consider that a 5.7L/350 Chevy-based
engine costs a boat dealer about $2,000 and retails for about
$3,100, while the Ford 230 hp-based engine costs about $2,400
and retails for about $3,200, there is plenty of room to save
your customer money and still make a good profit on your work.
Why shops stay away
Many shops shy away from marine work, particularly
complete engines, because they feel the liabilities are too great,
or because of misinformation on the design and operation of the
typical inboard marine engine. The misconceptions that marine
hardware is limited production stuff that can’t be found in the
normal automotive market, that the blocks and heads are high nickel
castings, and that if you install an automotive engine in a boat
it won’t last, are nonsense.
These untruths are often spread by OEM marine
engine manufacturers, and others to discourage their dealers from
seeking more cost effective alternatives in the automotive aftermarket.
The special equipment for marine use is mostly limited to coast
guard approved electrical and fuel systems designed to prevent
explosions and fires, as well as for marine water-cooled exhaust
systems. However, the basic engines, Chevy, Ford, and Chrysler,
are for the most part, the same cores you’ll find at your local
When Mercruiser, OMC, Volvo Penta, Crusader
and others develop a marine engine, they start with what is known
as a base engine from Chevy, Ford or Chrysler. They then "marinize"
it by adding their own proprietary exhaust manifolds, ignition,
electrical system, mounts, transmission or drive, and carburetion.
They sell these packages to the boat builder, who then installs
them into new boats.
These engines include the Chevy 181 cid in
four cylinder, a derivative of the Chevy II 153 engine; the 3.8L
and 4.3L V6; the 305, 350, 454 and 502 V8s; the Ford 302, 351
Windsor and 460; and the Chrysler 318, 360 and 440 V8s. The 350
Chevy represents about 70-75% of the market; the Chryslers are
not in production anymore. Very few of these engines run above
5000 rpm, so a quality job of engine building will produce an
engine that will last a long time.
In Chevrolet, the 3.0L/181 cid in four cylinder
is externally similar to the 153 four used in the early Chevy
II Nova. It’s now made in Mexico, and there are no automotive
related parts in it. The block, crank, rods, head and pistons
are all different. Finding a core other than the original is unlikely.
The 4.3L/262, 5.0L/305, and 5.7L/350 are the
same castings used in the automotive market. These engines are
two-bolt main, cast crank, cast piston, 9.0-9.4 compression ratio
engines. However, they do not use the ’86 and later swirl port
heads. The standard 4.3L/190-205 hp and 5.7L/250-260 hp engines
have 1.94 non-swirl heads. If you use the swirl ports, the engine
will be seriously down on horsepower.
The standard big block is the 7.4L (of course),
again with cast crank, two-bolt mains, 3/8 bolt rods, and the
small oval port truck heads. It’s an 8:1 motor with cast flat
top pistons. This engine is rated at 300-330 hp. Slightly higher
performance versions of these engines are available in what Mercruiser
calls its Magnum series engines.
Until recently, the small block was only available
as the basic 260. Now a 300 hp version is available, and I suspect
the principle improvements are the multipoint EFI, a better exhaust,
and possibly a slightly more radical camshaft combined with the
new vortec cylinder heads.
In the big blocks, the Magnum version of the
7.4L/454 is essentially a 1970 LS-6, with steel crank, 7/16 bolt
rods, four-bolt block, forged pistons, and square port heads.
It’s rated at 350 hp carbureted, or 385 hp fuel injected. The
8.2L/502 Magnum EFI is rated at 415 hp and is just a bigger bore
version of the 7.4L. Keep in mind that ’94 and later big blocks
are Gen. V versions.
Ford and Chrysler engines follow the same basic
parameters as Chevrolet in that they use the larger valve production
heads; the lower ends are basic light truck components. When Chrysler
was still building the 318 and 360, but had stopped production
of the 440, it bought 460s from Ford to round out its product
The various marine engine manufacturers also
offer a variety of high performance engines. For example, for
1997 Mercruiser’s highest horsepower regular engine is the 415
hp 502 Magnum, but its high performance line includes engines
like its supercharged 572 cid big block Chevy that makes about
900 flywheel horsepower. These are limited production engines,
built with OEM and aftermarket parts, and are not the subject
of this article because of their limited market and very high
cost. For 1997, Mercruiser’s SC 800 sells for $55,125; you even
get a transmission with it!
Even though these engines are based on automotive
production engines, and are built in the same factories, there
are some similarities and some differences that you need to be
aware of. Horsepower ratings are in accordance with NMMA (National
Marine Manufacturers Association) and are rated at the propeller
shaft, which will be from 10 to 30 hp less than a flywheel rating.
Head gaskets are embossed stainless steel or stainless core for
salt water application. Camshafts are more radical than the profiles
necessary for emissions-controlled automotive applications.
If you rebuild marine engines, you will eventually
run into an opposite rotation version. No big deal. Several aftermarket
gasket suppliers offer marine gaskets, and Wolverine makes a complete
line of standard and reverse rotation cams. I always add an extra
.001" to the piston minimum clearance, because the blocks
generally run cooler and the pistons hotter than a typical automotive
Marine specs are the same as automotive on
bearing clearances, and I make sure the rod side clearance is
to spec. Again, factory numbers work well, but I’ve seen mismatched
sets of rods and cranks that stack up with only .003" or
.004" between the rods; guaranteed to fry a bearing.
On the subject of valve seats, narrow is not
good, particularly on the exhaust side. The use of .060"
to .080" wide seats helps cool the valve and there isn’t
any significant penalty in flow. Stainless steel valves are a
good idea too. I’ve seen stock exhaust valves get so hot they
lose their heads under continuous full throttle use. With the
unleaded situation at the fuel dock, hard seats under the exhaust
valves are mandatory. GM even puts them in production marine heads
instead of just induction hardening them like it does in its trucks
Since these engines generally don’t see serious
rpm unless the driver jumps a wave with the throttle forward,
a lot of valve spring pressure is not needed. Just be sure that
the higher lift cam won’t coil bind the springs or bang the retainers
on the guide or seal. Big block Chevy stock passenger car springs
won’t work on the marine cam. I usually use a Crane 99839 in this
engine with the stock flat tappet cams. I use Pioneer RV 1011,
RV 1086, or Sealed Power VS 707, in small block Fords, and a Crane
99833 in 460s; VS 1120 Mellings work in the small block Mopars,
with no rotators. Of course, if you’re using performance cams,
you should use the springs recommended by the manufacturer of
If you build a reverse rotation (right hand
rotation) engine, remember to use the proper rear main and timing
cover seals. If the pistons have offset pins, install them with
the arrows, dots or whatever to the rear of the engine. Use the
correct cam and timing set (most right hand rotation GM engines
use a two-gear setup instead of a chain). For the record, standard/left
hand rotation is the same as automotive, and reverse/right hand
rotation is the opposite of automotive.
Also beware of the DIYer or the mechanic that
doesn’t know what he’s doing. I’ve had more than a few engines
ruined by someone that put a left hand engine in where a right
hand had been and by cranking the engine backwards sucked lake
water up the exhaust. They get suspicious that something is wrong
when water starts flowing out of the carburetor. As I’m sure you
can imagine, it’s never their fault!
Today, most if not all marinizers and boat
manufacturers use the oiling system provided on the base engines,
but some early boat manufacturers had their own set ups, such
as Chris Craft’s cast aluminum pans on some early models. In the
case of stock engines the best policy is to reuse or duplicate
the original set up.
"I really love my boat but I want just
five more miles per hour," is a common refrain heard annually
from many boat owners. It seems that anyone that owns a boat larger
than a canoe wants to go faster, and the guy that wanted five
more mph last year wants another five this year.
Marine rpm is different
While marine performance has many parallels
to other markets, the one thing that is not the same is rpm. For
instance, in drag racing, the common practice is to rev the engine
as far above the power peak as the next gear will drop it below
the power peak, giving the highest average horsepower. In any
situation where the highest top speed is required, the rpm where
maximum horsepower occurs will generate the highest speed.
The higher the rpm that you can generate any
given quantity of torque, the more horsepower the engine makes;
300 ft. lbs. of torque at 3000 rpm is about 170 hp, but if you
make the same 300 ft. lbs. at 6000 rpm, you have 340 hp. Twice
the rpm twice the horsepower. Simple enough, that’s why racing
engines are typically revved to their structural limits.
The problem with that concept in boats is that
many of the I/O drives will not live for extended periods above
5000 rpm because gear oil temps go out of sight. Even with additions
such as drive showers to cool the oil, the practical maximum is
around 6000 rpm. Of course, this varies with the amount of torque
applied to the gear train, but it’s a pretty good rule of thumb,
and cheaper, to stay on the conservative side (an overhaul on
a burnt up drive can cost more than your engine did).
Jet boats, V-drives and straight inboards are
not as critical in this area. If you have the experience to know
what your doing and your customer understands the risks and potential
costs associated with high rpm engines, there is more horsepower
available upstairs. Of course high rpm engines sacrifice low rpm
performance and flexibility, and they tend to be temperamental.
Any engine that makes peak horsepower above
6000 rpm is going to have a very nasty, lopy idle, be hard to
maneuver in tight areas or when loading on the trailer, and will
require carb adjustments every time the weather changes. And,
it may not idle slow enough to observe the no wake areas around
marinas and loading ramps without constantly shifting in and out
of gear. This means in marine applications, volumetric efficiency
is the name of the game, and not high rpm.
A few years ago, I spent a couple of hours
thrashing a 260 hp 350 Chevy on the dyno, looking for an inexpensive
performance kit that could be installed on an engine in the boat.
The goal was to produce more than 300 hp without exceeding 5000
rpm, with nothing more than a cam and intake/carb change.
I started with a stock fresh rebuilt engine
with stock 1.94 valve heads, fitted with stock marine center riser
manifolds, 3" risers, dry exhaust, stock marine cam, and
a stock cast iron intake with a marine quadrajet. After the initial
break in, the engine produced 249 hp on a 600 rpm/second acceleration
pull, and 269 hp on steady pull, at 4500 rpm. I was surprised
to discover that at 5000 rpm, horsepower increased to 273. That
got me thinking.
After 25 additional pulls to evaluate various
cams up to 284°/.469" lift (218° at .050"),
carburetor and intake manifold combinations, and a change to 4"
risers on the exhaust manifold, the engine finally made 302 hp
at 5000 rpm with a Cam Dynamics 272 hydraulic, 14096011 Chevrolet
intake ñ a cast iron version of the Z-28 aluminum high
rise, stock Q-jet and 4" risers.
A wolverine WG 1159 dual pattern cam with 280
int/290 exhaust duration (214/224 @ .050") and .465"
lift out pulled the Cam Dynamics 272 in the 2500 to 3500 rpm range,
but by 4000 rpm was falling behind and only made 295 at 5000 rpm.
A Cam Dynamics 278 made 310 hp at 5000 rpm and went to 319 hp
at 5250, but was unacceptable below 3000 rpm and would make a
boat harder to get on plane.
I tried 1.6 rockers on most of the cams, and
although probably a nice tuning tool, offered no startling improvements.
Fuel specifics for any of these combinations which included a
Holley 4781 (850 double pumper) and an 84018 (750 marine) carburetor,
were terrible, as high as .75 lbs/hp/hr, indicating that the engine
was at it’s limit in the breathing department.
Fuel specifics remained poor throughout, in
spite of efforts to rejet the carburetors to improve the situation.
The rejetting usually lost horsepower or made no significant change,
and was undesirable from the point of trying to use off-the-shelf
components. The cams were installed as ground, to minimize the
technical abilities of the installer.
"Holy cylinder heads Bat Man!"
At the conclusion of the cam tests, I installed
a set of 74 cc Dart/World Products heads which I had done minor
pocket porting on, with 2.02" and 1.60" valves. With
the Cam Dynamics 278 still in the motor, and the Chevrolet high
rise intake and Q-jet carb, horsepower jumped to 340 at 5000 rpm,
and the fuel specifics went from .73 to .58.
The substitution of the 750 Holley marine carb
added another 10 horsepower. Best yet, the horsepower at 3000
jumped from the stock 208, up to 223. A total of 44 runs was put
on this little mouse during the thrash. I feel confident that
optimizing this combination by decking the block or installing
the marine .018" stainless head gaskets, and surfacing the
cylinder heads to get the true compression up in the area of 9.5
to 9.75, advancing the cam a couple of degrees, and perhaps the
addition of 1.6 rockers, carb jetting, timing adjustments, etc.,
and this combination would be good for 370 hp or better.
That’s 100 hp over the stock engine with no
bottom end changes. A well done 377 could make well over 400 hp,
and the longer stroke would be a real kick in getting the boat
on plane. Hydraulic roller cams offer the advantage of faster
lift rates and higher lift for any given duration, which translates
into a broader power band and improved overall performance. Although
pricey, they are worth considering for the individual that wants
It’s my opinion that attempting to achieve
significant increases in horsepower without the attending increase
in rpm requires a conservative approach to camshaft selection
and a radical approach to cylinder heads, intake manifold and
exhaust systems. Currently, there is a proliferation of aftermarket
cylinder heads from Edelbrock, Brodix, Dart, World Products, Trick
Flow, Chevrolet and Ford, and maybe others that I have missed.
All of these companies offer aluminum heads
that are economical and will produce significant increases in
horsepower when installed on an otherwise stock engine. They are
available from the manufacturer already ported, and when combined
with other sensible modifications, make major increases in horsepower.
But be careful ñ aluminum and salt don’t get along well.
Aluminum heads will work fine in fresh water but unless the engine
is flushed with fresh water after every use, they won’t last long
in a salt water application.
Keep in mind that aluminum heads can handle
about a half point more compression than their iron counter parts.
The production heads on small block Fords are pretty poor when
it comes to making good horsepower; these engines really respond
to a good set of heads and intake.
For the customer who can’t afford these aftermarket
cylinder heads, a good porting of the stock castings is the next
best thing. Most production heads benefit from slightly larger
valves that allow the bowls and the approach to the seats to be
more favorably shaped. If you aren’t experienced and don’t have
a flow bench to evaluate your changes, it’s probably a good idea
to sublet this work, or order heads from a recognized racing head
shop. If you do it wrong, you may be worse off than if you just
did a good job reconditioning the heads.
Good marine exhaust systems are expensive.
A set of four-tube, double-wall stainless steel headers for an
offshore racer could set your customer back $12,000 or more. However,
most applications can use one of the variety of cast aluminum
manifolds available for about twice as much as stock ones cost.
Performance modifications will dictate through the transom exhaust
in most cases, because the 2" passage through the drive is
just too much of a bottle neck.
The primary consideration for aftermarket exhaust
systems are, of course, increased exhaust scavenging. But just
as important is to dump the water into the exhaust as far down
stream as possible, and to be sure the outlet is significantly
below the top of the riser portion. Longer duration cams have
a lot more reversion at low rpm, and with stock manifolds, they
will suck water back into the engine. If you have an unexplained
problem with the oil turning milky, this could be your problem.
If you are building a replacement for a freeze-cracked engine,
there is a high probability that the manifolds are junk too, so
why not solve two problems at once?
I purposefully avoided subjects on supercharges
and the like. I am not a fan of the Roots blower. Granted, it’s
a cheap way to get a substantial increase in power, and it looks
neat, but, in my opinion, the attending problems in engine durability
offset the advantages. The new generation of centrifugal blowers
and the old standby Paxton are another matter; I feel they have
potential. I think that the basics should be attended to first,
and then the blower added afterwards. An engine that makes good
power naturally aspirated, will make more power blown compared
to one that just has the blower bolted on. But that’s another
article in itself.
Sadly, the EPA is starting to have it’s effect
on the marine market, too. By 2006, marine engines must meet new
emissions specs. The good news is most of the changes will center
around two-cycle engines. In the inboard market we will see more
electronic engine controls and fuel injection systems, but things
like EGR valves, cats, and the multitude of other automotive controls
seem unlikely, at least in the near term.
I find it hard to imagine emissions tests for
boats, although I guess it could happen. Recent issues of Hot
Boat Magazine ran a series of articles on modifying a Mercruiser
502 Magnum, where about 80 hp was added to the stock 415. This
would be good reading for those interested in this market as the
502 Magnum is computer controlled EFI, and the article addresses
the problems of dealing with these computer controls.
If you are just getting into the marine market,
my suggestion is to go to boat dealers, boat shows, look at engine
installations, and read everything you can find on the subject.
In the performance side of the market be sure to consider the
ability of the boat owner to live with the package you sell him.
Some boaters get along fine with really radical stuff, but a far
larger percentage are over their heads before the boat’s off the
Ken Weber is former owner of Marine Engine
Service, Inc., a production engine rebuilding business that specialized
in inboard marine engines. Currently employed as an automotive
extended claims adjuster for General Electric Capital Corp., Denver,
CO, Weber builds six to eight marine performance motors annually.