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Making A Big Splash In The Marine Market

By Ken Weber

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 of today.

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 bone yard.

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 line.

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 application.

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 and cars.

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 the cam.

Reverse rotation

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 the best.

Component selection

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 trailer.

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.

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