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The average individual that would have owneda performance car in the 1960s, and the baby boomers that did,in many cases no longer have a modern affordable toy they cantweak to their own satisfaction. Serious performance today isoften available to only a few with large checking accounts orextra good credit, and even for those that can afford it, thehigh tech "compucar" is beyond the ability of many whenit comes to performance enhancements.

Computer controlled everything, intertwinedlike a grapevine, often makes it difficult for all but the mostdedicated gear heads to make modifications that suit personaltastes. 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 starkcontrast to the emission-restricted performance street vehiclesof today.

Most importantly for machine shops and enginerebuilders, a major part of the marine market uses automotive-basedengines. The growing interest in rebuilt marine engines, bothstandard and high performance, has expanded the need for machineshops and production engine remanufacturers (PERs) serving thismarket. It’s a market that includes engines ranging from productionremans to super exotic, i.e., cost as much as a house, to 1,000hp-plus monster motors.

Based on information provided by aftermarketgasket suppliers, marine engine OEMs and others already supplyingthis market, it is estimated that the total demand for replacementmarine engines represents more than 20,000 units annually. Thetwo largest areas of this market demand involve engines that weren’twinterized properly where the blocks, heads and manifolds sufferedfreeze cracks (many first time boat owners are under the impressionthat when the boat’s out of the water, the water is out of theengine); and engines run in salt water that over five to 10 yearshave rusted from the inside out.

In either case, the cores are often not rebuildableand you have to include a core in the price of your rebuilt engine.Surprisingly, only a small percentage of the engines replacedevery year are actually worn out from use. In boating, 100 hoursa 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-basedengine costs a boat dealer about $2,000 and retails for about$3,100, while the Ford 230 hp-based engine costs about $2,400and retails for about $3,200, there is plenty of room to saveyour customer money and still make a good profit on your work.

Why shops stay away

Many shops shy away from marine work, particularlycomplete engines, because they feel the liabilities are too great,or because of misinformation on the design and operation of thetypical inboard marine engine. The misconceptions that marinehardware is limited production stuff that can’t be found in thenormal automotive market, that the blocks and heads are high nickelcastings, and that if you install an automotive engine in a boatit won’t last, are nonsense.

These untruths are often spread by OEM marineengine manufacturers, and others to discourage their dealers fromseeking more cost effective alternatives in the automotive aftermarket.The special equipment for marine use is mostly limited to coastguard approved electrical and fuel systems designed to preventexplosions and fires, as well as for marine water-cooled exhaustsystems. However, the basic engines, Chevy, Ford, and Chrysler,are for the most part, the same cores you’ll find at your localbone yard.

When Mercruiser, OMC, Volvo Penta, Crusaderand others develop a marine engine, they start with what is knownas 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 installsthem into new boats.

These engines include the Chevy 181 cid infour cylinder, a derivative of the Chevy II 153 engine; the 3.8Land 4.3L V6; the 305, 350, 454 and 502 V8s; the Ford 302, 351Windsor and 460; and the Chrysler 318, 360 and 440 V8s. The 350Chevy represents about 70-75% of the market; the Chryslers arenot in production anymore. Very few of these engines run above5000 rpm, so a quality job of engine building will produce anengine that will last a long time.

In Chevrolet, the 3.0L/181 cid in four cylinderis externally similar to the 153 four used in the early ChevyII Nova. It’s now made in Mexico, and there are no automotiverelated parts in it. The block, crank, rods, head and pistonsare all different. Finding a core other than the original is unlikely.

The 4.3L/262, 5.0L/305, and 5.7L/350 are thesame castings used in the automotive market. These engines aretwo-bolt main, cast crank, cast piston, 9.0-9.4 compression ratioengines. However, they do not use the ’86 and later swirl portheads. The standard 4.3L/190-205 hp and 5.7L/250-260 hp engineshave 1.94 non-swirl heads. If you use the swirl ports, the enginewill 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 thesmall oval port truck heads. It’s an 8:1 motor with cast flattop pistons. This engine is rated at 300-330 hp. Slightly higherperformance versions of these engines are available in what Mercruisercalls its Magnum series engines.

Until recently, the small block was only availableas the basic 260. Now a 300 hp version is available, and I suspectthe principle improvements are the multipoint EFI, a better exhaust,and possibly a slightly more radical camshaft combined with thenew vortec cylinder heads.

In the big blocks, the Magnum version of the7.4L/454 is essentially a 1970 LS-6, with steel crank, 7/16 boltrods, four-bolt block, forged pistons, and square port heads.It’s rated at 350 hp carbureted, or 385 hp fuel injected. The8.2L/502 Magnum EFI is rated at 415 hp and is just a bigger boreversion of the 7.4L. Keep in mind that ’94 and later big blocksare Gen. V versions.

Ford and Chrysler engines follow the same basicparameters as Chevrolet in that they use the larger valve productionheads; the lower ends are basic light truck components. When Chryslerwas still building the 318 and 360, but had stopped productionof the 440, it bought 460s from Ford to round out its productline.

The various marine engine manufacturers alsooffer a variety of high performance engines. For example, for1997 Mercruiser’s highest horsepower regular engine is the 415hp 502 Magnum, but its high performance line includes engineslike its supercharged 572 cid big block Chevy that makes about900 flywheel horsepower. These are limited production engines,built with OEM and aftermarket parts, and are not the subjectof this article because of their limited market and very highcost. For 1997, Mercruiser’s SC 800 sells for $55,125; you evenget a transmission with it!

Even though these engines are based on automotiveproduction engines, and are built in the same factories, thereare some similarities and some differences that you need to beaware of. Horsepower ratings are in accordance with NMMA (NationalMarine Manufacturers Association) and are rated at the propellershaft, which will be from 10 to 30 hp less than a flywheel rating.Head gaskets are embossed stainless steel or stainless core forsalt water application. Camshafts are more radical than the profilesnecessary for emissions-controlled automotive applications.

If you rebuild marine engines, you will eventuallyrun into an opposite rotation version. No big deal. Several aftermarketgasket suppliers offer marine gaskets, and Wolverine makes a completeline of standard and reverse rotation cams. I always add an extra.001" to the piston minimum clearance, because the blocksgenerally run cooler and the pistons hotter than a typical automotiveapplication.

Marine specs are the same as automotive onbearing clearances, and I make sure the rod side clearance isto spec. Again, factory numbers work well, but I’ve seen mismatchedsets 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 notgood, particularly on the exhaust side. The use of .060"to .080" wide seats helps cool the valve and there isn’tany significant penalty in flow. Stainless steel valves are agood idea too. I’ve seen stock exhaust valves get so hot theylose their heads under continuous full throttle use. With theunleaded situation at the fuel dock, hard seats under the exhaustvalves are mandatory. GM even puts them in production marine headsinstead of just induction hardening them like it does in its trucksand cars.

Since these engines generally don’t see seriousrpm unless the driver jumps a wave with the throttle forward,a lot of valve spring pressure is not needed. Just be sure thatthe higher lift cam won’t coil bind the springs or bang the retainerson the guide or seal. Big block Chevy stock passenger car springswon’t work on the marine cam. I usually use a Crane 99839 in thisengine with the stock flat tappet cams. I use Pioneer RV 1011,RV 1086, or Sealed Power VS 707, in small block Fords, and a Crane99833 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 ofthe cam.

Reverse rotation

If you build a reverse rotation (right handrotation) engine, remember to use the proper rear main and timingcover seals. If the pistons have offset pins, install them withthe arrows, dots or whatever to the rear of the engine. Use thecorrect cam and timing set (most right hand rotation GM enginesuse a two-gear setup instead of a chain). For the record, standard/lefthand rotation is the same as automotive, and reverse/right handrotation is the opposite of automotive.

Also beware of the DIYer or the mechanic thatdoesn’t know what he’s doing. I’ve had more than a few enginesruined by someone that put a left hand engine in where a righthand had been and by cranking the engine backwards sucked lakewater up the exhaust. They get suspicious that something is wrongwhen water starts flowing out of the carburetor. As I’m sure youcan imagine, it’s never their fault!

Today, most if not all marinizers and boatmanufacturers use the oiling system provided on the base engines,but some early boat manufacturers had their own set ups, suchas Chris Craft’s cast aluminum pans on some early models. In thecase of stock engines the best policy is to reuse or duplicatethe original set up.

"I really love my boat but I want justfive more miles per hour," is a common refrain heard annuallyfrom many boat owners. It seems that anyone that owns a boat largerthan a canoe wants to go faster, and the guy that wanted fivemore mph last year wants another five this year.

Marine rpm is different

While marine performance has many parallelsto other markets, the one thing that is not the same is rpm. Forinstance, in drag racing, the common practice is to rev the engineas far above the power peak as the next gear will drop it belowthe power peak, giving the highest average horsepower. In anysituation where the highest top speed is required, the rpm wheremaximum horsepower occurs will generate the highest speed.

The higher the rpm that you can generate anygiven quantity of torque, the more horsepower the engine makes;300 ft. lbs. of torque at 3000 rpm is about 170 hp, but if youmake the same 300 ft. lbs. at 6000 rpm, you have 340 hp. Twicethe rpm twice the horsepower. Simple enough, that’s why racingengines are typically revved to their structural limits.

The problem with that concept in boats is thatmany of the I/O drives will not live for extended periods above5000 rpm because gear oil temps go out of sight. Even with additionssuch as drive showers to cool the oil, the practical maximum isaround 6000 rpm. Of course, this varies with the amount of torqueapplied to the gear train, but it’s a pretty good rule of thumb,and cheaper, to stay on the conservative side (an overhaul ona burnt up drive can cost more than your engine did).

Jet boats, V-drives and straight inboards arenot as critical in this area. If you have the experience to knowwhat your doing and your customer understands the risks and potentialcosts associated with high rpm engines, there is more horsepoweravailable upstairs. Of course high rpm engines sacrifice low rpmperformance and flexibility, and they tend to be temperamental.

Any engine that makes peak horsepower above6000 rpm is going to have a very nasty, lopy idle, be hard tomaneuver in tight areas or when loading on the trailer, and willrequire carb adjustments every time the weather changes. And,it may not idle slow enough to observe the no wake areas aroundmarinas and loading ramps without constantly shifting in and outof gear. This means in marine applications, volumetric efficiencyis the name of the game, and not high rpm.

A few years ago, I spent a couple of hoursthrashing a 260 hp 350 Chevy on the dyno, looking for an inexpensiveperformance kit that could be installed on an engine in the boat.The goal was to produce more than 300 hp without exceeding 5000rpm, with nothing more than a cam and intake/carb change.

I started with a stock fresh rebuilt enginewith stock 1.94 valve heads, fitted with stock marine center risermanifolds, 3" risers, dry exhaust, stock marine cam, anda stock cast iron intake with a marine quadrajet. After the initialbreak in, the engine produced 249 hp on a 600 rpm/second accelerationpull, and 269 hp on steady pull, at 4500 rpm. I was surprisedto discover that at 5000 rpm, horsepower increased to 273. Thatgot me thinking.

After 25 additional pulls to evaluate variouscams 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 hpat 5000 rpm with a Cam Dynamics 272 hydraulic, 14096011 Chevroletintake ñ a cast iron version of the Z-28 aluminum highrise, stock Q-jet and 4" risers.

A wolverine WG 1159 dual pattern cam with 280int/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 hpat 5250, but was unacceptable below 3000 rpm and would make aboat harder to get on plane.

I tried 1.6 rockers on most of the cams, andalthough probably a nice tuning tool, offered no startling improvements.Fuel specifics for any of these combinations which included aHolley 4781 (850 double pumper) and an 84018 (750 marine) carburetor,were terrible, as high as .75 lbs/hp/hr, indicating that the enginewas at it’s limit in the breathing department.

Fuel specifics remained poor throughout, inspite 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-shelfcomponents. The cams were installed as ground, to minimize thetechnical abilities of the installer.

"Holy cylinder heads Bat Man!"

At the conclusion of the cam tests, I installeda set of 74 cc Dart/World Products heads which I had done minorpocket porting on, with 2.02" and 1.60" valves. Withthe Cam Dynamics 278 still in the motor, and the Chevrolet highrise 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 carbadded another 10 horsepower. Best yet, the horsepower at 3000jumped from the stock 208, up to 223. A total of 44 runs was puton this little mouse during the thrash. I feel confident thatoptimizing this combination by decking the block or installingthe marine .018" stainless head gaskets, and surfacing thecylinder heads to get the true compression up in the area of 9.5to 9.75, advancing the cam a couple of degrees, and perhaps theaddition 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 nobottom end changes. A well done 377 could make well over 400 hp,and the longer stroke would be a real kick in getting the boaton plane. Hydraulic roller cams offer the advantage of fasterlift rates and higher lift for any given duration, which translatesinto a broader power band and improved overall performance. Althoughpricey, they are worth considering for the individual that wantsthe best.

Component selection

It’s my opinion that attempting to achievesignificant increases in horsepower without the attending increasein rpm requires a conservative approach to camshaft selectionand a radical approach to cylinder heads, intake manifold andexhaust systems. Currently, there is a proliferation of aftermarketcylinder heads from Edelbrock, Brodix, Dart, World Products, TrickFlow, Chevrolet and Ford, and maybe others that I have missed.

All of these companies offer aluminum headsthat are economical and will produce significant increases inhorsepower when installed on an otherwise stock engine. They areavailable from the manufacturer already ported, and when combinedwith 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 engineis flushed with fresh water after every use, they won’t last longin a salt water application.

Keep in mind that aluminum heads can handleabout a half point more compression than their iron counter parts.The production heads on small block Fords are pretty poor whenit comes to making good horsepower; these engines really respondto a good set of heads and intake.

For the customer who can’t afford these aftermarketcylinder heads, a good porting of the stock castings is the nextbest thing. Most production heads benefit from slightly largervalves that allow the bowls and the approach to the seats to bemore favorably shaped. If you aren’t experienced and don’t havea flow bench to evaluate your changes, it’s probably a good ideato sublet this work, or order heads from a recognized racing headshop. If you do it wrong, you may be worse off than if you justdid a good job reconditioning the heads.

Good marine exhaust systems are expensive.A set of four-tube, double-wall stainless steel headers for anoffshore racer could set your customer back $12,000 or more. However,most applications can use one of the variety of cast aluminummanifolds available for about twice as much as stock ones cost.Performance modifications will dictate through the transom exhaustin most cases, because the 2" passage through the drive isjust too much of a bottle neck.

The primary consideration for aftermarket exhaustsystems are, of course, increased exhaust scavenging. But justas important is to dump the water into the exhaust as far downstream as possible, and to be sure the outlet is significantlybelow the top of the riser portion. Longer duration cams havea lot more reversion at low rpm, and with stock manifolds, theywill suck water back into the engine. If you have an unexplainedproblem 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, sowhy not solve two problems at once?

I purposefully avoided subjects on superchargesand the like. I am not a fan of the Roots blower. Granted, it’sa cheap way to get a substantial increase in power, and it looksneat, but, in my opinion, the attending problems in engine durabilityoffset the advantages. The new generation of centrifugal blowersand the old standby Paxton are another matter; I feel they havepotential. I think that the basics should be attended to first,and then the blower added afterwards. An engine that makes goodpower naturally aspirated, will make more power blown comparedto one that just has the blower bolted on. But that’s anotherarticle in itself.

Sadly, the EPA is starting to have it’s effecton the marine market, too. By 2006, marine engines must meet newemissions specs. The good news is most of the changes will centeraround two-cycle engines. In the inboard market we will see moreelectronic engine controls and fuel injection systems, but thingslike EGR valves, cats, and the multitude of other automotive controlsseem unlikely, at least in the near term.

I find it hard to imagine emissions tests forboats, although I guess it could happen. Recent issues of HotBoat Magazine ran a series of articles on modifying a Mercruiser502 Magnum, where about 80 hp was added to the stock 415. Thiswould be good reading for those interested in this market as the502 Magnum is computer controlled EFI, and the article addressesthe 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 engineinstallations, and read everything you can find on the subject.In the performance side of the market be sure to consider theability of the boat owner to live with the package you sell him.Some boaters get along fine with really radical stuff, but a farlarger percentage are over their heads before the boat’s off thetrailer.

Ken Weber is former owner of Marine EngineService, Inc., a production engine rebuilding business that specializedin inboard marine engines. Currently employed as an automotiveextended claims adjuster for General Electric Capital Corp., Denver,CO, Weber builds six to eight marine performance motors annually.

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