Auto engine marinization

Discussion in 'DIY Marinizing' started by Guest, Jun 10, 2002.

  1. Guest

    Guest Guest

    Hi. Can anyne help me find resources (preferably on the net but any will do) on how to marinize an auto engine. I know of one book that describes the process but it is out of print and difficult to get hold of. Any help appreciated.
  2. Jeff
    Joined: Jun 2001
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    Location: Great Lakes

    Jeff Moderator

    The questions to start with would be gas or diesel, salt or fresh water?

    I'm not a mechanic, but here is a repost of a usenet message which Rod McInnis posted in response to a similar question - there must be a few how-to's on the Internet but I don't have links off-hand - spending an hour or so with Google is probably a good bet:

    Do you want it to be legal? Do you want it to be safe? Do you want it to last a long time?

    The longevity is an issue with the raw water cooling, especially if the boat will ever see salt water. An automobile engine is cooled with, preferably, antifreeze, but even straight water will neutralize itself and stop eating away at the metal parts. On a boat, you have a constant flow of new water, which leads to a higher rate of corrosion. Two areas that are usually "marinized" are the head gasket and freeze plugs. If you are rebuilding the engine anyway, get the marine head gasket, and make sure the freeze plugs are brass instead of steel.

    Safe and legal are mostly fire/explosion issues dealing with the fuel and electrical system.


    The marine carburetor will be a little different, designed so that the float bowls don't vent into the engine compartment, although the differences are rather subtle (at least to my eye).

    The fuel pump has one major difference: it is designed to contain the fuel in the event of a ruptured diaphragm. It is common for a fuel pump to fail by rupturing the diaphragm, which allows gas to leak onto the side where it wasn't intended to be. This gas will then either leak out onto the ground or into the crankcase. For a car, onto the ground is preferred, but on a boat either case is really, really bad! A standard solution to this problem is to have a double diaphragm, with a drain between them. If the primary diaphragm ruptures, the gas will be contained by the second diaphragm and flow out the drain. This drain typically has a hose (usually clear) attached to it which leads up to the carburetor intake. Any gas that leaks is dumped into the carb, and if the leak gets bad enough it will flood the engine, which is a lot better than blowing you to smithereens!


    Starter, alternator: rotating shafts with electrical contacts, they make sparks! Sparks will ignite fumes! To prevent the sparks from blowing up the entire boat, a marine starter and alternator will have flame suppression on the cases. The starter and alternator are NOT sealed, they have what is essentially a flame arrester between the source of sparks and the outside. It is possible for a small amount of gas fumes to enter the starter/alternator and be ignited, but the case will hold the small explosion and the flame arrester will prevent the fumes in the boat from being ignited. This flame arrester may look like nothing more than a small screen, but it is so important!

    Distributor: Same flame arrester idea as the starter. The advance curves for an automobile are usually not the best for a boat, so you are better off with a marine distributor anyway.

    While the fuel system modifications are intended to prevent any combustible fumes from being accumulated, the electrical system is designed to not ignite any such fumes that might be present. You may consider it redundant, but there are other ways to get gas fumes in
    (such as while refueling) and other sources of ignition.

    I highly recommend that you purchase the marine versions of the starter and alternator. You may choke when you see the price tags, but consider this: gas fumes are heavy, they settle to the bottom. The starter is located about as far down as anything can be. Gas fumes are most likely to settle when the boat is idle, which means that the starter is most likely to be the first electrical item operated. Starters, with out a doubt, make sparks. In other words, the greatest hazard comes from the starter.

    Rod McInnis

    And another:


    I had a target engine (off the shelf from a dealer) rebuilt when it spun a bearing. The rebuilders used a different cam (for the nature of the use rather than highway), racing timing gears and chain (usual higher revs than automotive) and brass vs. steel freeze plugs.

    Dropping in the marine electronics (mine was carb, so your application might be different) including the brain and distributor (no spark) completed the deal. Runs like a champ.

    So, there's not all that much different. If you don't already have the exhaust manifolds, that will be extra, but isn't really marinizing the 'engine' - and you'll want the marine alternator and starter, probably, too, for the same no-spark reasons. So, all the "hang-on"s will likely have to be bought new or used, but the engine itself doesn't need much modification.

  3. Jeff
    Joined: Jun 2001
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    Location: Great Lakes

    Jeff Moderator

    And some other on-topic posts from over the past year:

    From: John

    It can be done since Merc, OCM and Volvo do it all the time. Remember to:
    1. Change to Brass freeze plugs
    2. Change the Alternator, Starter and Distributor to their respective Marine Versions
    3. Change the Air Filter to a USCG Flash suppression type.

    From: Bryon Kass

    Also add change camshaft, circulator pump, head gaskets, thermostat, carb, intake and exhaust manifolds, bell housing, flywheel, and anything else I forgot. Bryon Kass webmaster and Custom Design
    150 Mechanic St. Foxboro, MA 02035
    508-543-9068 or fax 508-543-5127, Foot yard 508-384-2415 in THE ENGINE ROOM

    From: Stephen G. Lusardi

    Justin, I'm not sure of you're engine knowledge or skills, but be advised that this task can only be done by very knowledgeable, experienced people or you will have lots of trouble. The following points must be observed.
    1) A car engine is a LIMITED duty engine and a marine engine is a continuous duty engine.
    2) There are many differences in the following: a. Ignition advance curve b. Valve timing (camshaft) c. Oiling system d. Cooling system. e. Exhaust system f. Carburetor g. Air cleaner h. Alternator I. Starter Please remember when it breaks, you cannot call AAA for service. You become a burden on others, give boating a bad name and risk lives unnecessarily. Please be responsible and do this correctly. Steve

    From: Augusto Queiroga Valentim If you do you will regret it........sooner or latter! Probably rather soon. Boats demand a lot of power, and automobile engines are not engineered for continuous full power duty, as marine engines are.

    From: Vacuo

    It is always assumed that the auto engine installed in a boat is going to be operated at WOT ( wide open throttle) since this fits the behavior pattern of most boaters. But there is no reason why an oversized engine cannot be installed instead, say 2 or three times the displacement. Thus the auto engine can loaf along at 2500 rpm which is near the peak of its torque curve, and thus enjoy maximum fuel efficiency. With the right choices the available power at this rpm will be just what the boater requires.

    Thus, a Rabbit diesel is the equivalent of a 20 to 25 hp marine engine- no more. Fine for propelling a sailboat or other displacement hull.


    From: Marcus G Bell

    Right. When an auto engine is marinized, it's peak HP rating is derated by a fraction. Also, many boaters "cruise" at less than WOT.

    The auto engine uses something like 25% of its rated HP to keep the car moving at steady highway speeds. The marine engine very often is cruised at 50-75% of its rated power, which corresponds to something like 33-50% of the peak power of the "same" engine rated for land use.

    So a marine engine works harder than a car engine, but it is more steady work than experienced by the auto engine upon which momentary high loads are placed.

    -- -- Marcus.

    From: John

    Marcus Iam trying to figure this out, What is the exact difference between a Marine engine and an auto engine of the same displacement by the same manufacturer other than the obvious (Freeze Plugs, Starter, Distributor ect.) Lets take the Chevy 305 V8 which is used by Merc and Volvo. What are the other difference? If I had to guess I would say the cam is different maybe the heads but what else? In addition I believe that the blocks used are base on truck blocks rather than car blocks.

    From: Stephen G. Lusardi

    Marcus, There are many differences between a limited duty engine and a continuous duty one. As an example , it is necessary to understand the difference between an SAE work test and a standard BRAKE test. Both tests are performed on the same device called an engine brake or engine dynamometer. Essentially the engine is run up against a variable load. This load device is mounted in bearings so it can rotate, but it is prevented from rotating by a lever which is attached to a scale. This scale will read out in ft. lbs.. So at any engine speed the maximum torque can be read. Because torque is one component of horsepower and speed being the other, horsepower can be calculated as well as fuel consumption, brake mean effective pressure and a number of other items. The important thing is the test program. A BRAKE test is where the engine is warmed to normal operating temperatures and then run up to maximum power and that's the end of the test. An SAE test, on the other hand is run up against the load for a sustained period (maybe 4 hours) until the maximum power is reached that DOES NOT exceed acceptable manufacturers operating parameters like oil, water, exhaust and head temperatures and pressures. In your example you mentioned the Chev. 305. This engine will brake somewhere around 220 to 280 HP depending on state of tune. The maximum SAE rating of this engine is 55 HP.

    I suggest that if you were flying on a plane, or on an ocean cruise ship, you would want the engines tested under an SAE test program. The differences in design and build are many. Intelligently, you have to factor the type of usage you need from the engine and then modify the automotive engine accordingly. The greater the durability, the greater the cost. Nothing is for free and when a marinized automotive engine costs are comparable to the standard automotive variety, you must question it's durability. Steve

    From: bro

    i have a 1972 buick 455 that i plan to put in a 18 ft flat bottom v-drive so far i have chnaged the freeze plugs to brass and i am changing all bearings and gaskets but what should i do on the camshaft ??? thanks jon

    From: Stephen G. Lusardi

    Jon, The Camshaft should be the least of your concerns. If you intend to to be able to run this engine at more than 1/2 throttle for any length of time, your biggest problem is cooling. Automotive engines do not cool evenly when under heavy load. If you check the water flow diagram for your engine you will see that cool water enters the engine in front by the pump, proceeding rearward gaining heat eventually exiting the block through the steam riser holes into each head between each cylinder. Then the water runs forward within the head exiting to the intake manifold, then the thermostat housing and then back to the radiator. The net effect is that the front cylinders get more cool water than the rear. The two center cylinders have less surface area for cooling as well, so run hotter than the ends of each bank. Continuous duty engines and long track NASCAR engines are modified so that there is a water distribution log mounted on each bank in the lifter valley, under the manifold in an attempt to even the cooling a bit. They run forged crankshafts, cored con rods for spray oil cooling of the bottom of the pistons and many other refinements that have little value when running in a limited mode, but have extensive value when running in a continuous mode. They have high temp. resistant stainless steel valves, stellite valve seats, better guides and oil seals. They use low cam lobe acceleration rates, wider valve centers typically 112 degrees as opposed to performance cams at 106, lighter valve springs to save effort and stress on the valve train. They use thermostatically controlled oil coolers, larger volume oil pumps, larger oil filters that are also incidentally full flow and the list goes on. If you are going run in circles on a lake, carry a set of oars and have little regard for repair costs, I guess these changes are of little value to you. If however your needs are a bit more stringent, please consider a proper marine engine.

    From: SAIL LOCO

    <<<<<<<The Camshaft should be the least of your concerns. If you intend to to be able to run this engine at more than 1/2 throttle for any length of time, your biggest problem is cooling. Automotive engines do not cool evenly when under heavy load. If you check the water flow diagram for your engine you will see that cool water enters the engine in front by the pump, proceeding rearward gaining heat eventually exiting the block through the steam riser holes into each head between each cylinder. Then the water runs forward within the head exiting to the intake manifold, then the thermostat housing and then back to the radiator. etc. etc.>>>>>>>

    I have never seen any engine where the water flows to the heads last. Water always goes to the heads first since that is the hottest part of the engine. The water in every engine enters at the water inlet on the intake manifold and imediately enters the heads water passages.

    From: Marcus G Bell

    Many, if not most auto engines have the water leaving the bottom of the radiator and entering the pump first. The pump then delivers the coolant to the bottom of the block. Half of the pump volute is often cast integral with the block, and the main pump outlet is then a passageway cast directly into the block's water jacket. A small hose delivers some flow to the intake manifold and the manifold drains into the head, but the bulk flow to the head comes upwards from the block. The thermostat is in the top of the head and the hot fluid leaves the engine through the thermostat.

    The flow of coolant through the engine and radiator follows the direction of natural convection. Hot fluid comes into the top of the radiator where it cools and falls, then flows into the bottom of the engine where it heats and rises. The pump assists the convection. It is the rare consumer-grade automobile engine which operates in opposition to this convection, and I know of none of the top of my head. So, I find the statements "Water always goes to the heads first" and "water in every engine enters ... the intake manifold" to be misleading and/or incomplete.

    -- -- Marcus.

    From: KPB314159

    I don't know where this thread started, but I can tell you I have seen many converted auto engines spread out on a dock, waiting for delivery of some replacement frammitz. Most of the problems that could be categorized fell into the cooling area: cracked manifolds, cracked heads, carbon and other problems from running too cold, etc. One common problem is that if things are misadjusted it is possible to shoot very cold lakewater or seawater directly to a hot engine which would never be expected by the designers of an automotive engine. Ken Bowen

    From: Wallace Waggoner

    Original thread revolved around the differences auto vis marine engines. Does anyone really believe GM has a seperate dision building differnent components for its 5.7 sold to Volvo and Mercruiser? Of course not. You can purchase a parts list for any Ford or Chevy based Marine engine from your local car/truck dealer. Check it out for yourself and see if you can justify the price charged for your boat engine. Marine manufactures have a sweetheart deal with Ford/Chevy. You and I can not go to a dealer and purchase one of their marine longblocks for $2200. You must purchase in the quantity of Redline et al and be a "certified" OEM marine engine builder.

    The Marine Industry has been pulling the wool long enough. In the are Its even worse regarding diesel and outboards.


    From: Wallace Waggoner

    Outside water-cooled exhaust and the optional FWC Volvo and Mercruiser by a GM engine changed very little from the new engine you purchase from a dealer to put in your car.

    Talk to any performance engine builder in your area. He has catalogs for any parts you need for a long block put to marine use. Stellite seats will cost you abbout $8 and stainless valves another $8 a piece. Another $20 for better grade of Clevite bearings.

    A marine engine needs low end torgue. You get this by NOT spending huge quantities on high performance heads and trick cams. Standard reliable parts and machining are key. Obviously a few more dollars in incresed cost of Coast guard approved and mandated parts.


    From: krulik

    This is all well and good but what are the differences in the construction of the engine. Using that Chevy 305 again, Now, If I change the rear end gear from a 3:23 to a 4:11 that will increase the amount the engine will have to work to maintain the same speed what other changes are needed to the engine? If marine engines can sustain more revs with a greater load they should be used in auto racing? Seems that this would be the next logical step.


    I've found this thread to be especially interesting, especially the parts of it that deal with the power ratings of the engines. I'm much more familiar with diesel engines than with gasoline ones, (such that I can quote the spec's of some of the more common ones without having to look them up). So, the examples that I will site pertain directly to diesel engines, but the exact same principles apply to gasoline engines. In fact, I?ll use the CAT 3208 as an example, since it is a V-8 diesel very similar to a large gasoline engine. (636 cid)

    The harder you run an engine, the faster you will wear it out. It really is as simple as that. Every engine therefore has many different power ratings, depending upon how hard you plan to run it and how long you want it to last. If I were to tell CAT that I was going to put the engine into a small commercial fishing trawler that was going to run 3500 hours pre year, for example; then they would tell me that the 3208 was good for 150 hp. They would derate the engine so that I could not get more than that much power out of it. If you were then to ask them for an engine for a high performance recreational boat that was not going to be used more than 300 hours per year, then they would tell you that the same engine was good for
    435 hp.

    What?s the difference between these two identical engines, that they would have such a different rated power? Chiefly this: In both cases CAT wants for the engine to last at least as long as the warranty. Since I?m going to put a whole lot more hours onto my hypothetical boat than you are, they will derate mine in order to achieve that objective. In another example, I was once going to put a CAT 3412 into an air boat. My customer wanted the most power for the weight and the cost, but was happy with an engine life of at least 1800 hours. This is a very unique case, in which CAT was willing to rate the engine at 1000 hp. On the other hand, a friend of mine maintains a fleet of work boats with this same engine in them. He runs them at about 500 hp and gets 50,000 hours between overhauls.

    CAT has five different power ratings published for each engine. (If you present them with a special case, you will learn that they actually have more ratings than that.) These ratings go from "A" for continuous duty to "E" for highly intermittent duty. In this example, the A rating for a 3208 is 150 hp; whereas the E rating is 435 hp. Gasoline engines have a similar ratings system, except that the DIN and ISO standards for "automotive power" ratings will give you a slightly higher number than most "highly intermittent" ratings. In other words, it is the peak power you might use if you were passing uphill. It is certainly not the amount of power that you can expect the engine to put out for any significant period of time.

    We are currently building two boats, both commercial fishing work boats; and are about to buy an engine for one of them. It will most likely be a Cummins B5.9 in one of its many versions. This is the same engine Ford used to offer in their pickup trucks, and Dodge currently offers. Cummins is telling me that they will rate it for
    150 hp in our boat, but it is rated at 220-250 in its various automotive applications, and it is offered in a 300 hp version for recreational marine uses that do not exceed 300 hours per year. To put this into perspective, a pickup truck running flat and level at 75 mph without a trailer will require about 50 hp. The same truck with perhaps a 10,000 lb. gross load would require most of the 220 hp. The same engine in a 25 foot sport fishing boat would probably cruise at about 200-230 hp.

    There is a difference between the way commercial truck engines and car engines are rated. (A pickup truck is a car for the purposes of this discussion.) In the case of a diesel truck engine, they are rated pretty much at the power they are operated at. In a gasoline car engine, however; they are rated much higher than you would ordinarily ever use them. I know of another example that illustrates that point nicely. They are two almost identical 35 foot sport fishing boats that typically run over a 100 miles off shore together, where they troll for deep water fish. One has twin Cummins 6B5.9 engines salvaged out of pickup trucks and converted to marine use. The other has twin 454?s, also salvaged out of automotive service and converted. All four of these engine are rated at 250 hp, or within five percent of it. These boats normally stick close together all weekend, until it is time to run home; at which time the diesel boat will beat the gasoline boat home by about six hours. The difference is that Cummins recommends that the diesel boat back off of maximum rpm by only 200; whereas no one is going to run a gasoline engine that hard for that long. That captain backs off about a thousand from maximum rpm. To exceed that speed for long periods of time causes cooling problems. This is very consistent with the way the engines were designed to operated during their first lives as automotive engines.

    To sum it all up, an automotive engine will typically run at 20-40 percent of its rated power. (In this case, I?m using "automotive power ratings.") It will only exceed these limits under highly unusual circumstances. If you put the same engine into a recreational boat, it will typically run at 60-80 percent of its rated power. A commercial diesel truck engine typically runs at about 60 percent of its rated power. (Flat, level, 75 mph, maximum legal gross load.) That same diesel engine installed into a recreational boat will often run at up to 95 percent of its rated load, with bursts perhaps as high as 105 percent. If these same engines are installed into commercial work boats, then their service lives would be more similar to the truck or the car. It is all a matter of how long you expect to run your engine before replacing it or overhauling it.

    All the numbers I quoted in this article are from my memory. If I were at work, where I have all my reference books, I would have checked them more carefully. They should be fairly accurate, and are certainly good enough for the comparison purposes for which they were intended. Since the same engine is sold in so many different versions, you would certainly want to check the OEM specifications on your particular engine before making any critical decisions based upon these numbers.

    From: Rick Morel The above really says it all. I'm more familiar with auto engines used in aircraft, but this is very much like marine use. Except it's a lot easier to drop the hook and look for a tow than start looking for a possible landing site! Know what the prop on an airplane is for? To keep the pilot cool -- turn it off and watch him sweat!

    Aircraft engines are much derated for reliability. The old Continental
    65HP was used in racers at about 120HP, for a life of a couple hundred hours instead of a couple thousand.

    VW engines have been used a lot. In the car, they're rated at about
    60HP for the 1,600cc. In planes, if they're derated to 40-45HP, they seem to last forever. If used at 60HP a few hundred hours. Then there are the "high HP" conversions, claiming 85 and more. The life of these seem to be in minutes!

    My brother used to build dragsters years ago. He'd get 1,800HP out of Chevy 454.... for three drags. About 30 seconds.

    I think someone mentioned a Subaru engine in this thread. The
    4-cylinder and 6 have been used on gyroplanes with good results. I forget the spec HP rating for the 4, but used at about 50HP makes for a very reliable and long-lived engine.

    To maybe put things in some perpective, the VW is rated at 5,200 RPM, if I recall right, but is set up in aircraft for 3,800 RPM take-off and about 3,600 RPM cruise. The Subaru 4 has I think the same spec RPM, but is used at 4,000 and 3,800.

    One more question I remember was how much HP does an average sedan take for 60 MPH? Now, getting to my EV (Electric Vehicle) period. My Electric Ford Escort Wagon took 12.5 HP for 55 MPH. A Ford Ranger pick-up requires 19.2 HP for 55 MPH. Less than we would think. The big difference in HP required (and gas/electron milage) is due almost all to aerodynamics.



    [much good aviation comparisons snipped]

    A good way to approximate the amount an engine puts out under any given set of circumstances is fuel consumption. Figure a diesel engine burns about one gallon per hour per 20 hp. The number for a gasoline engine is about 15. These numbers can vary quite a lot for certain applications, but they are good general numbers.

    By them, my Honda Civic requires about 22 hp @ 60 mph, and 34 hp @ 75 mph. My dad's F250 (3/4 ton Ford pick up truck), requires 60 hp @ 60 mph when running empty; and 104 hp at the same speed when fully loaded with his 30 foot RV trailer.

    I know a heavy recreational passagemaker-trawler (49 ft) that requires
    60 hp at 7.5 knots. By the same reckoning, a 25 foot sport fishing boat running at full speed with the same engine requires 300 hp. I've got the same engine, a CAT 3208, in a piece of heavy equipment at work, and it averages about 175 hp. Message 36 in thread From: Mike Goodwin ( Subject: Re: car engine conversion Newsgroups: View this article only Date: 1999/05/26

    I take it that this is done with the governor on a diesel to limit RPM's , how is it done in a gas engine?


    Actually, that is not how it is normally done in a diesel engine. Rather, you will likely find different injection pumps, different injectors, and different computer settings in different engines of the same type that are rated at different power levels. Most often, you will find two engines rated at different power levels to actually run at the same rpm shaft speed, but sometimes the higher rated engine will run a little faster. In some such cases, the moving parts will be better balanced in the faster turning engine; and may even be made of a lighter alloy; but in most cases nothing is done inside of the engine when they are rated at higher shaft speeds.

    Another way that is often used for both gas and diesel engines is to control how they are used. A particular boat may be geared and proped such that it can only put a 200 hp load onto an engine at 2800 rpm, for example; whereas the same boat owned by someone else could be geared and proped to place 300 hp on the same engine.

    As for how to "dump down" a gasoline engine, I guess that the carburetor or the fuel injector would be the easiest place to do so without putting a higher parasitic load onto the engine. If the engine is computer controlled, then that may also be used, just like with some diesel engines.


    They were fairly standard conversions; basically the same thing that you would have had if you where to buy the marine version of either one of these engines. They both had wet marine exhaust manifolds and heat exchangers fresh water cooling. The gasoline engines had the "fire proof" marine carburetor, distributor, alternator, and starter; as well as a flame arrestor on the carburetor. I don't know what cams they might have had in them; and I'm pretty sure that the heads and pistons were original.

    If you have a high interest in this, then I'd suggest picking up a copy of "Inboard Motor Installation," by Glen L. Witt and Ken Hankinson. It is available through Glen-L Marine Designs, 9152 Rosecrans, Bellflower, CA 90706. The ISBN is 0-939070-01-4. They cover the subject in good detail that is easy to understand. This includes not only the engine itself; but also every aspect of how to install both it and the transmission.

    From: Credence Vision Systems LLC

    Truly 'marinizing' motors starts on the design table. The differences go right through the whole engine: Large (sometimes roller type) main bearings on the crank shaft between every 2 connecting rods, different stroke on the motor (more torque at lower rpms), different compression ratio (lower), different cam, different carburetor etc. They take the same basic motor as what is produced for a car, beef up the bearings and make small adjustments to bring the horsepower and torque curves a little lower on the rpm curves. Externally, there are tons of differences intended to make the motor fit in a tight compartment, sometimes use a generator instead of an alternator, and the cooling system is redesigned around the new motor. Go to a boat show and look at the 'Vortec' Chevy engines designed for marine use. Nothing like the 'Vortec' Chevy engines that go in cars, except maybe the block/heads/valve covers and the like are the same.

    I'm not sure what 'marinizing' would mean after the fact on a motor, e.g. after a motor was built for car use. Car engines do work fine, but they don't last as long. Using a motor in a marine application is equivalent to running a car at full throttle up steep hills for a long time. They just don't last as long like that. Same problems exist for converting car engines for homebuilt airplane use. It's not done much because they become unreliable after a short time, including all those Volkswagon engines that people have used in airplanes. I guess what it comes down to is what kind of a good deal you got on your automotive engine versus the price of the marine engine, and whether or not the ongoing replacement costs and what not work out to your advantage or not. If you don't hotrod your boat but instead drive it more reasonably and spend long hours fishing or cruising more slowly, then your automotive engine may last just fine. Rule Number One: Change the oil like you change your socks, and use top quality brands
    (Castrol) or synthetics (anybody's.) Buy a new crankshaft and put it, along with new main bearings, into the motor before first installation, then follow Rule Number One.


    From: Ron Eike

    A year or so ago one of the boat magazines (it may have been WoodenBoat) ran an article on marinizing a Suburu diesel. Maybe you could get some help here.


    From: Steve

    One of the major problems of putting a car engine in a boat is the need for water cooled exhaust manifold and the clutch/reverse gear. First, a large part of the heat generated is going to go through the exhaust manifold. You need to build a water jacketed manifold. I've tried insulating them but it doesn't last long. Second, the clutch and transmition from a car are totally in appropriate for marine manuevering. The reverse is geared way to low to be usefull. A automatic doesn't solve that problem and also needs a cooler since there isn't any air flow around it. Also you need a thrust bearing which a car transmitions doesn't have. The prop shaft will be pushing against the output shaft on the transmition and will distroy the ball bearing in the final dive.

    My experience and opinion, FWIW.

    Steve s/v Good Intentions

    From: Craig M

    Ok, here goes. First let me say I am a marine mechanic and I only use webtv for the newsgroups. It`s easier and I can`t get a virus. You can use a car engine in a boat, but it won`t last long. Pay attention now, there will be a quiz later. A marine engine has a stainless head gasket. Raw water will rust yours out. Marine engines have different cams, they perform from idle up, a car starts making power around 2 grand. A boat has different pistons, they have more silicone as not to expand as much due to long periods at high rpms. Electronics are sealed cause the spark factor. Exhaust is water cooled so you don`t burn up your boat. Now, think of this: A boat is on 80% load 90% of the time, a car is on
    20% load 90% of the time. A car will never run wide open all day, yet a boat will. It`s all cause of the above. Of yeah, if you still use the escort engine, don`t let the coast guard inspect your boat. You will get busted cause of the solenoid not being marine also the started and alternator.
  4. Jeff
    Joined: Jun 2001
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    Jeff Moderator

    The book you referred to was Marine Conversions by Nigel Warren ISBN # 0229116787 or ISBN # 0229117708 (1982)?

    Maybe someone else will jump in and have some better links for you as well.
  5. Guest

    Guest Guest

    Thanks for all the info. Am I to take it from this, that most people think it is a bad idea to use a marinized auto engine and just raise the extra cash for a purpose built marine motor?
  6. Portager
    Joined: May 2002
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    Location: Southern California

    Portager Senior Member

    That Depends

    That depends on two things.

    How far are you going off shore and how far can you swim?

    If the first exceeds the second, then spend the money on an engine you can rely on.

    Just my 2¢

    Mike Schooley
  7. Jeff
    Joined: Jun 2001
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    Location: Great Lakes

    Jeff Moderator

    I wouldn't go quite that far... then again, I'm thinking of a twin installation so even if one fails you can limp home on the other ;)

    I bought an old Wellcraft with twin 351's 9 years ago because it was all I could afford at the time - I've used it mostly for island hopping and short day trips - the longest about 50 miles, and for that the converted automotive engines are ok. The first month I had the boat, I did end up with a cracked engine block due to a very small amount of water which found its way into the carburator somehow (no shield over the carb itself - just a Holley flame arrestor and the engine hatch) and that was quite a frustration. I also went through a waterpump and when I had to replace a starter (three times!) I wished it was in a better location (which it would have been if it was a marine engine rather than on the very bottom where you could only feel your way around rather than actually being able to see it.

    Just depends on your budget, use, skill, and how reliable you require it to be. Mercruisers are also based on automotive blocks - so if you are a skilled mechanic, it's not an impossible task to create a good marine engine. But if you go far enough to be as good, I'm not sure what the cost difference would be (negative or positive.) As Mike says, if I had been going further offshore or if my budget at the time would have allowed, I would go for the real deal if at all possible.
  8. Portager
    Joined: May 2002
    Posts: 418
    Likes: 13, Points: 0, Legacy Rep: 325
    Location: Southern California

    Portager Senior Member

    Auto Conversion Engines

    In retrospect I think my response sounds a little harsh.

    My interest is long range "Passagemaker" boats which are almost always single engine diesels. Auto conversion engines don't make sense in this application.

    OTOH as Jeff pointed out, they are fine for twin engine coastal cruising applications. Now that I think about it, maybe that is why so many gas powered boats have twins and so many diesel powered boats are singles.

    Personally, I think one high reliability engine would be lower cost and much less maintenance than two low cost, low reliability engines, but to each his own.;)

    Mike Schooley
  9. Guest

    Guest Guest

  10. Guest

    Guest Guest

    There exists a book on the marinisation of engines.
    This book is not available. But some libraries have it, and there you can copy the relevant passages.
    In Germany the Library of the University of Hamburg has it.
  11. gonzo
    Joined: Aug 2002
    Posts: 15,877
    Likes: 1,249, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Marine blocks have a high chromium content for corrosion protection. The crankshaft is hardened. Also the camshaft is different from an automotive because the load and rpm usage are different.
  12. Guest

    Guest Guest

    Stainless Steel Heat Exchangers

    Who can supply Stainless Steel Heat Exchangers to fit a GMC 6.2L
    Diesel V8
  13. gonzo
    Joined: Aug 2002
    Posts: 15,877
    Likes: 1,249, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Heat exchangers are made of bronze or monel. Stainless steel will corrode. What configuration of heat exchanger do you need? It is necessary to know shape, size, hose connection positions and bracket type.
  14. Gypsy72
    Joined: Mar 2004
    Posts: 9
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Naples, FL

    Gypsy72 Junior Member

    regardless of gas or diesel, one thing you can not forget is ventilation,
    ventilation, ventaltion.
    the ambient air temp in the engine room must not get too high.
    this will cause loss of power and possibly engine damage.
    as for gas installs, fumes of course is the issue.
    make sure that your natural ventilation does the job completely on its own.
    blowers are there for other reasons.
    the engine manufacturers will have the numbers your looking for concerning this matter.
    Also be concerned,when converting automotive to marine (gas or diesel), with coolers and there placement in the system.
    having a oil cooler or a fuel cooler in the wrong sequence could produce temp problems.
    all in all, converting is more hassel then its worth when your talking gas. marine engines are plentiful and affordabale.

  15. GizmoStang
    Joined: May 2004
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Indianapolis, IN

    GizmoStang New Member

    I look of good points here for the electronics...

    But a few issues about the use of Automotive Engines... Mercruiser and OMC both utilitzed late 70's early 80's GM Small Blocks that are if anything weaker than installed and any GM Truck.

    They had the same factory Teflon coated Timing Set that was a major downfall to GM Automotive engine for years.

    With the Price Merc wants to charge for "Std Marine" engine components you can purchase Race Quality parts ran out at the max redline you will ever dream of running a boat engine at for a fraction the cost and have a much more solid engine then Merc or OMC ever made, especially since neither ever even bothered to use a 4 bolt main block to strengthen the bottom end of their motor.

    Sorry but if an SBC can handle 10,000 - 12,000 rpms tasked of it in drag cars or long distance circle track driving it will be more than enough to run 4500 - 5000 rpms in a boat all day long. Anything over that range you put your lower unit in serious risk of anyways. By the Way Pre-OD Tranny Cars & trucks cruise indefinately @ 4500 rpm's for well over 100,000 miles...

    Use Graphite Race Head Gaskets, High Quality (Clevite or Michigan) Bearings, find a good Comp or Crane Marine Cam and put it together and have no worries of the engine being the cause of your problems

    Use the Marine Water Pump, Brass Freeze plugs... You can even pickup up used Marine starter/Alternator on Ebay and fully rebuild for 1/2 the cost of new ones, 90% are Delco Products and can be rebuilt with standard Automotive Brushes, Bearings and such which will still retain the flame protection and run like new.

    Personnally I'd go with a stock GM Hei distributor and simply substitute the advance weight springs, its a much more reliable system and will never fail.
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