Mercedes V8 & V12 Big Block Conversions

[ATMHC]

I've been dreaming of building a replica of one of the classic 1930's style mahogany runabouts (26' to 32') powered by a beautifully polished big Mercedes 6.9 Litre V8 or one of the newer Mercedes 6 Litre V12 gas engines. The 6.9's are dry sump motors that are virtually indestructible. They produce a huge amount of smooth & reliable horsepower and torque, and are surprisingly inexpensive to come by. The V12's are smoother still, & with polished valve covers & 6 pipes coming out of each side, would be reminiscent of the old Packard & Kermath V12's used in the speedboats of yesteryear.

Has anyone heard of any German companies offering marinizing kits for any of these engines ???

I can't be the first lunatic to think of this... If anyone has had any experience doing this or has any constructive ideas at all I'd love to hear them.

[FAST FRED]

marinizing kits for any of these engines ???

Very little is needed to marinize an engine. The exhaust can be dry and asbestos (or better) wrapped . A keel cooler will handle the cooling loads with minor drag.


But "cheap" Mercedes? How?


FF

[charmc]

You can buy used Mercedes Benz engines here:

http://www.hartsautoparts.com/mercedes/Engine.html

[ATMHC]

Reply to Fast Fred:

The big block gas V8's made by Mercedes for the 600 series limousines, known as M-100 engines were made from the 60's in 6.3 litre size and then in the 70's in 6.9 litre size. Roughly 1800 6.9 sedans were sold in the USA, many of which are now considered junk because of bad body rust problems which are simply too expensive to properly fix in relation to the market value of the cars. The car also suffered from a complex hydro-pneumatic suspension system which often cost owners several thousand dollars to repair & replace.. that factor, plus their rather poor gas mileage, has created a rather large supply of these cars on the market & they can therefore be bought pretty cheap... I have 3 at the moment, one that I drive occasionally, one nice rust free example that I'm planning to restore (the paint is faded pretty badly from being outside in Arizona) and another rust free parts car that I bought for under a thousand dollars... Over the years I've owned about 6 or 7 of these cars, and I've never had a motor failure, even in cars with well over 100,000 miles on the clock. This is largely due to the fact that these engines employ dry sump lubrication systems. Due to the superior lubrication afforded by those systems, these engines simply never wear out. Another reason for their long life is the fact that they were designed to propel a huge limo at speeds of 125mph, and consequently, in a standard Mercedes sedan, which weighs considerably less than the limo, they really are ever called upon to work very hard... A 6.9 sedan is truly a 140 - 150mph car...easily capable of cruising with 4 or 5 passengers at 125mph for extended periods, if you can find a place to do that legally... 9 times out of 10, if you get a 6.9 with anywhere between 100 to 150,000 miles on it, all you would have to do to insure that it will run smoothly for another 100,000 plus miles is replace the timing chain and the timing chain tensioners, (plus other belts, hoses, water pump, etc...) While I've never experienced a 6.9 engine failure, I have heard that a badly stretched or broken timing chain is usually responsible for their failure on the rare occasions that they do fail... If you do not understand why the dry sump feature insures their long life, send me an eMail with your telephone # & I'll call you to explain it... too long to type & explain here...

I understand the marinizing process insofar as the exhaust and cooling is concerned, although I wonder how big a keel cooler would have to be to cool such a big beast of an engine, and especially how one would go about installing one in the belly of an antique wooden speedboat... Since the boat wouldn't be used much, I was thinking that direct salt water cooling would be OK as long as the cooling system was flushed out with fresh water after each use.

What I don't know about is mating the engine up to a proper marine transmission, and, as the fuel injection system on these engines is a bit complex, I'd love to find out if anyone makes a manifold capable of converting these engine to carbueration... I think a polished block with four big dual throat Weber carbs on top would really look great and probably, with the help of a free flow exhaust system, increase their power output by a good margin... I suspect that there must be high performance accessory companies in Germany, similar to our Edelbrock etc, that make high performance goodies for these big engines... I have no idea how to find out who they are and where they are however...

If you've never experienced the performance of a Mercedes 6.3 or 6.9 I highly recommend them.. As a toy used only occasionally their fuel consumption should not be a problem. With their enormous torque, they would also make a great vehicle to use to tow an antique speedboat on its trailer.

[Ike]

The Mercedes 450 SEL 6.9 produce in the 1975 was my dream car. Never could afford one.

[mydauphin]

AS someone said...
Marineizing exhaust, cooling, etc... not problem

Custom hookup to marine transmission capable of handling torque. Perhaps if you got one with a standard transmission ma be it could be adapted.

May be you can get older model with simpler computer that handled just basic ignition and fuel control.

All things considered... not a fast or cheap project... but may be fun. What is weight of one of these engines...

[ATMHC]

The M-100 Mercedes engines ONLY came with automatic transmissions, and one generation of fuel injection components. Switching to carbueration is not absolutely required... In fact the engine would probably run smoother without it... but in order to maintain the visual appeal of a "race boat" under the hood so to speak, it would look cooler...

These engines are not light.. I don't know the exact weight but a mechanic friend of mine assures me that they are no heavier than a big block Chevy V8 and probably much lighter than the old Packard V12's...

[mydauphin]

I thought these engines where Aluminum block and heads. I would think they are lighter than Chevy. You need to know weight to know how to mount engine and where. Also exact HP and torque figures are good to setup tranny and prop. I dont think Auto transmission would last long. But worth a try... for fun. A 23 foot boat is marginal with 2 engines this size. I would go with single engine with Levi Drive or Duo-prop

[ATMHC]

Mercedes didn't switch to Aluminum blocks until the 80's, the M-100 big blocks were cast iron.

If anyone's interested, there's an excellent website all about the old Mercedes big block engines:

http://www.m-100.cc/

Frankly I'm surprised that these haven't already found there way into the high performance boating arena. They are far superior to their American big block cousins which still reply on push rods rather than the overhead cam design of the Mercedes. With proper maintenance they virtually last forever, and I believe that you could probably get an easy 600-700 horsepower out of them if you were sufficiently motivated...

[marshmat]

Frankly I'm surprised that these haven't already found there way into the high performance boating arena. They are far superior to their American big block cousins which still reply on push rods rather than the overhead cam design of the Mercedes. The boating industry's not one to adopt anything different with regards to power, not without a fight. The standard gas engines that just about everyone uses - 4cyl 3.0, 6cyl 4.3, 8cyl 5.0, 8cyl 5.7, 8cyl 7.4- are all ancient designs, that have been in use more or less forever (at least from my perspective at the younger end of the boatowners' scale). They work, spare parts are everywhere, so why bother digging out something new and different that might be better, but isn't an absolute 100% certainty? This is the philosophy that keeps new and possibly better options out of the mainstream.
As to the big Mercedes motor:
The engine might be able to handle boat-type loading conditions with relatively few mods- I'm not that familiar with it. But being in an enclosed environment (the bilge of a boat) it will need to have proper marine flame arrestors, spark-proof starter/alternator/other electrics, etc. or there's a good chance you'll blow the engine fifty feet in the air when you turn the key after it's been sitting for a while.

[ATMHC]

Reply to Marshmat;

I didn't mean that I expected the big block Mercedes to make a serious dent in the performance boat market.. but rather that I was surprised that those few lunatics out there with unlimited funds, who put Ferrari & Lamborghini engines in their boats, haven't tried these because by comparison to the Italian exotica, they are very cheap indeed. They also put out far more torque.

Mercedes, through it's MTU division, already has a big chunk of the market for Marine diesels from roughly 800 to 12,000hp. I'm surprised that they haven't gone into the smaller end of the marine diesel market with the excellent 6 cylinder CDI car diesels they make as a starting point. Mercedes makes a really small state of the art 1.7 litre (102 cubic inch) diesel for some of the really small cars that they sell outside of this country. That small diesel is so good that it's already been converted (by a company called Theilert) for use in airplanes, in fact you can buy 4 seat twin engine turbo diesel that outperforms the best twin gasoline engined counterpart for less than half the cost & with operational costs of considerably less than half per mile flown. If you want to see it, here's a link.

Go to: http://www.diamondair.com and select the DA42 Twin Star

Volkswagen is now marketing it's automotive CDI V6 diesel to the marine marketplace, and I suspect others will follow..

As to whether or not it's a 100% certainty that the overhead cam Mercedes engines are vastly superior to the outdated pushrod V-8's that Detroit is still pumping out, that's easy... It's 110% certain... One of my neighbors drives a 1984 500SEL Mercedes that he bought new and it currently has close to 400,000 miles on the clock with no major engine repairs ever... Did you ever see a Cadillac on the road with more than 150,000 miles on it that has not had an engine rebuild ?

[Ike]

Yes you would have to do some marinizing. As was said, a flame arrestor, the alternator and starter would have to be igntion protected, the wiring and hoses would all have to be replaced with stuff that meets Coast Guard standards. Even the fuel pump would have to be changed. Perhaps this is why no one has ever done it.

However, if it was in a completely open boat, that is the engine is sitting out in the open, about the only thing you would have to install is a flame arrestor or some sort of ram air induction that would direct backfires away from the interior and passengers. It would be one hell of a ride.

[Northwester]

Almost everything about a marinized gasoline engine is different from their land based cousins.

Here's a short list of most everything that is different:

-carburetors
-crankshafts (usually forged)
-cam shaft profiles
-ignition advance method (centrifugal only)
-ignition advance profile
-exhaust manifolds
-vapour/explosion proof starter, alternator, distributor
-lower compression ratio
-valves and valve seats
-waterpump capacity and thermostat
-frost plug and head gasket materials

Even if you did find the a set of marine manifolds for your engine, you would likely suffer from major detonation/overheating/reliability problems without making a lot of modifications. Most auto engines are not designed for the severe/continuous duty cycle of marine service in a planing hull vessel. The conversion would probably work for a while in a small displacement hull where the power demands and loading of the engine are much lower.

[marshmat]

Good points, Northwester.
An approach to modifying engines that may help to clarify matters is to look not at what type of vehicle the engine is propelling, but instead to look at what it will be expected to do with its output shaft. After all, it just sits there spinning a metal stick, not knowing or caring what that stick is connected to in the end.
The spark-proof electric auxiliaries are mandatory for a boat, unless you like fireballs in your engine room.
How much of the other mods are required depends on what the engine was originally built to do.
A typical car engine's duty cycle is mostly loafing around at about 1/4 to 1/3 of max RPM, with most of the remaining time being idling. Only once every few minutes is it expected to come anywhere close to its rated power, and then only for ten seconds or so at a time. So although it's tuned to be able to produce that rated power if asked to, most of its internals are optimized to run reliably and efficiently at the low-speed cruise.
Stick the engine in a boat, and it's now facing a completely different duty cycle. Now it's being asked to output 80% of full power on a constant basis. Hence why modifying a car engine for serious boat duty might involve beefing up the innards, changing cam and ignition, etc.
But wait- look at a truck engine. Nobody expects a truck to accelerate like a bullet, but it has a hell of a lot of drag. Its engine is going to be running at near-maximum power on a regular basis, and its owner expects it to last for close to a million kilometres before finally kicking the bucket. Put it in a boat, and the duty cycle hasn't changed that much. Same deal with a car engine that was originally built with track/racing work in mind; it was originally engineered to run constantly at near-full power and it will be happy to do so. But try running a Windstar's V6 at WOT for eight hours and you'll have problems. It all depends on the duty cycle for which the engine was originally designed and built.

[ATMHC]

Thanks to Marshmat & Northwester for their comments.. I'm sure that all of their points are valid.... Marshmat's comparison of a car engine to a truck engine actually applies very well to my original question, as the Mercedes 6.9 litre V8 has attributes of both.

The big block Mercedes V8's (used in the Mercedes 600 Limo, the 6.3 & the 6.9 sedans) were originally designed to propel a 7,000 + pound car (the big limo) at speeds of 125 mph plus. These cars were in fact used for extreme high speed cruising on the German Autobahns which had no speed limits... In its final iteration, enlarged to 6.9 litres for use in the 450SEL 6.9 sedan, it produced enough power to propel this 4,500 lb car to 60mph in 7.4 seconds and a top speed of over 140mph. The engine produced over 400 lbs of torque.

My experience over several long distance highway jaunts out west, where the car loafed along at 100mph at about 3,000 RPM, makes me think that given the proper marine specific modifications mentioned above, it would be ideally suited to powering a traditional narrow beam speedboat at cruising speeds in the 30 to 35 knot range, with the potential for significantly higher speeds if called for.... I was not thinking of using it in modern high performance boats where speeds are significantly higher.

What you have to keep in mind in order to properly evaluate this is the extraordinary quality of this engine's design and the high tolerances to which it was built. These were hand built engines, made for the most expensive car in the world in the late 70's. The 6.9 engine option added 42% to the base price of the top of the line S Class sedan made back then... in today's dollars, it would probably be a $125-150,000 car.

The dry sump lubrication system, holding 12.7 quarts of oil, insured that the engine was always properly lubricated, and the use of an oil cooler as standard equipment helped insure that the beast didn't overheat... Even with the oil cooler however, it didn't idle smoothly with the A/C running in downtown Phoenix traffic unless it was moving along... As long as air was entering the grill it was OK, but when it was stopped in bumper to bumper traffic, the temp guage went straight up real fast... even with the aux fan running.

The only thing that really concerns me about using this engine in a boat is the cooling system.. since I doubt that there are stock fresh water cooling marine manifolds that can be bought off the shelf, my thought was to go with a simpler salt water cooling system which I think would be OK given the fact that the boat wouldn't be run very often, would be kept on a trailer in my barn when not in use, and would always be flushed out with fresh water after each use. Perhaps more complex a problem would be the choice of whether to try to use the original Bosch fuel injection system or switch to carbs...

I'm still hoping that I'll find a marine performance equipment manufacturer in Germany who has already solved these problems and who has all the parts needed for the conversion for sale... If anyone reading this thread has any contacts in Germany, I'd appreciate it if you could pass this question along and post any replies you may receive..

Thanks to all...

[Northwester]

I own a '91 BMW ///M5. It comes from the factory equipped with a 3.6l inline 6 cylinder DOHC engine that develops 310 HP @ 6900 R.P.M. You can run the engine all day @ 6000 R.P.M. if you want as it is basically a detuned racing engine designed for that kind of duty cycle. Great German engineering but I digress.....

Back to your project. Your concept is neat and I appreciate what you're trying to accomplish. However unless the following details are considered and reengineered, your engine will probably not last very long in service.

-at minimum, you will need stainless exhaust valves and hardened exhaust valve seats otherwise the stock seats and valves will probably burn, the valves and seats are probably going to be very difficult to source
-a thicker head gasket made of stainless steel to lower the compression ratio and provide the required corrosion resistance
-a custom fabricated water cooled stainless tubular exhaust system
-if the cylinder head(s) or water circulating pump impeller are made of aluminum, raw water cooling is out of the question so add a raw water pickup pump which you'll need anyhow and a heat exchanger from big block chevy marine engine
-you'll need a different thermostat which is probably tough to source
-don't forget the vapour proof starter and alternator
-aftermarket programmable fuel injection system that allows removal of distributor and uses coil packs to fire the plugs
-replace all the frost plugs with ones made of brass
-replace the oil cooler with one made for marine use

If Mercedes engineered all of the cooling passages properly and all of the heat that is generated can be carried away, your engine has a chance of lasting provided that you do lower the compression ratio to a modest 8.0:1. Otherwise as I said before, the engine will likely suffer serious damage from detonation unless you plan to run high octane gasoline.

A crate big block chevy marine is probably going to cost less than it will cost you to marinize the 6.9l Mercedes engine in the end. For the little guy, it's seldom cheaper to do-it-yourself marinize because you don't have the volume purchasing power the big corporations have.

[marshmat]

The only thing that really concerns me about using this engine in a boat is the cooling system.. since I doubt that there are stock fresh water cooling marine manifolds that can be bought off the shelf, my thought was to go with a simpler salt water cooling system
I don't like the thought of such a special motor getting raw seawater rammed through the block. You shouldn't need many custom parts to convert a stock freshwater cooling heat exchanger, perhaps one meant for the popular 7.4 V8.
What's wrong with the fuel injection system that you wouldn't want to use it? That's as much a part of the engine's character as anything else...

[ATMHC]

I simply don't know enough about the mechanicals to answer your question.. If I put the boat in the water 10 times a year, for no more than a half day at a time, and then flushed it out thoroughly with fresh water.. how could it really be damaged by the salt water..? I assume there would be a strainer on the intake to prevent anything bigger than plankton from getting in the engine...correct ?

The only reason I'd consider switching from F.I. to carbs would be to achieve more of a vintage race boat look...

[marshmat]

It probably wouldn't be damaged by the saltwater in that kind of service. But if it were my boat (your priorities may differ) and I were the one spending the thousands of dollars to marinize a special engine, I would think the peace of mind and the knowledge that I didn't have to flush, would outweigh the extra few hundred bucks and few hours of routing coolant hose involved in adding a separate, generic (not engine mounted) heat exchanger, and piping corrosion-resistant coolant through my motor instead of nasty filthy seawater.
I agree with Northwester that the spark-proof starter, alternator etc. are essential; however, I'm not convinced that so much internal reworking is needed, given the duty cycles you've described for the engine (hauling really heavy, really fast cars at supralegal speeds) and the boat (leisurely loafing around in the mid-planing speeds with the occasional quick flyby past the Donzis). Someone who knows this engine would be better suited to comment than I, though.

[ATMHC]

If it is indeed that easy to create a safe & reliable fresh water cooling system, then I'd probably do so... I've just been under the perhaps mistaken impression that it isn't that simple to do...

[ATMHC]

For more detailed info on the 6.9 Mercedes engine, check out the following link:

http://www.m-100.cc/6point9/brochure/engine/index.html

[old750]

I know this is an old topic, but has anyone seen a modern mercedes 3.2L or 4.0L CDI (210-250hp) in a boat? I'm thinking it would be great on gas and fast enough for a 20' runabout. I've been searching all day for an engine source and so far only found the one give on this thread

(http://www.hartsautoparts.com/mercedes/Engine.html)

Anyone in Germany have anything?

[FAST FRED]

extra few hundred bucks and few hours of routing coolant hose involved in adding a separate, generic (not engine mounted) heat exchanger, and piping corrosion-resistant coolant through my motor instead of nasty filthy seawater.

All you need is a thru hull, water circ pump heat exchanger and water outlet.

The heat exchanger Mfg will direct you to correct sized unit.

FF

[TollyWally]

I realize this is a bit flippant but if one wants a mercedes v 12 diesel in a boat why not use a M.A.N. ? A wee bit spendy but... just asking.

[Jimbo1490]

I know 400 Lb-ft seems like a lot of torque to you, but remember that a stock Chevy 502 makes well over 500 Lb-ft. and is probably within 50 lbs dry weight if the M-B 6.9 V8. With the plethora of aftermarket high performance and marine parts available for the big block Chevy engine, it's hard to justify committing resources to something different that is highly unlikely to be better than the current standard.

Jimbo