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Old 12-05-2003, 09:02 AM
  #21
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I am impatient to see it produced and tested. Another interesting subject is the BMW-Victory Team joint venture. They marinized a BMW 4.4 V8 block and won two Class 2 championships in a row with those engines in their 35' cat. However, now they're talking about working on the 760 motor which is a 6 liter V12. They want to take it closer to the 8.2 liter displacement limitation of UIM Class 1 racing and possibly supercharge it. It produces 445 hp as it is now so it could be quite something with all those changes. I am convinced that with modern tecnology, a gasoline engine can produce 100 hp/liter, rev 6000 RPMs and last for over 500 hours without any problems.

So guys, sharpen your pencils and start writing to Mercury...

And GLH, I asked the same question but ZE GERMANZ from MTU decided to do it that way so better don't ask. Even Seatek use a sequential turbo system on their racing engines. I think it's a performance issue because turbos are driven by exhaust gases which means that if the motor is already spinning 1700 RPM (out of 2350) when the second turbo is let off its leash, it provides a real kick. I've been on a boat powered by four twin-turbo Seateks and the acceleration is better when the second turbo kicks in than anywhere else in the RPM range. However, this moment of force is a source of big problems. I've got a gearbox on my hands where shaft has jumped off the pinion or whatever you call it, because of that sudden boost. I was explained by ZE GERMANZ that they use a special production technique where the casing is closed and sealed and the internals put in place by putting them under 3000 bars of oil pressure. Great! How I'm going to recreate 3000 bars of oil pressure, that I do not know.
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Old 12-05-2003, 09:09 AM
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BTW, the worst thing for longevity is the bang-bang system where turbos are kept spooled up and spinning all the time, even below their activation RPM limit. This is designed to reduce the so called "turbo lag" and provide maximum pressure as soon as you hit the throttle. But it does funny things to engine internals...
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Old 12-05-2003, 11:58 AM
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Aren't Serpentine blowers "a la" Prochargers or Vortec spooling kind of chargers also?
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Old 12-05-2003, 01:47 PM
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Spooling chargers? No, that term applies to compressors whose turbine speeds are not tied to crankshaft speed. An exhaust turbo won't spin very fast at low engine speeds because a) it doesn't have much input energy from the exhaust stream and b) it is pumping against a mostly closed throttle plate. You yank the throttles open and it takes some time (inertia) and then as it begins to build boost, the exhaust stream responds with increased thermal energy which further drives the turbine. The point at which the turbine goes from "mostly coasting" to "pumping like mad" is considered to be the "spool up" point.

Engine-driven blowers have rotational speeds tied directly to crank speed so they have no "spool up". The fact that centrifugal blowers do make more and more boost with increased rotational speed is indeed a characteristic, but is different from a spool up condition.

It is interesting to note that a diesel turbo application will spin the impeller MUCH faster at cruise than a gas turbo application - thisis because the gas motor has physical throttle plates choking the turbo and causing it to spin against a load while the diesel just blows it on thru the motor freely.

As far as why we don't have a gazillion BMW V8 powered boats scattered all over the lake the answer is very very simple. Cost.

Take note that in addition to the ancient cast iron lumps we have in most boats, there have been commercially available:
* ZR-1 Corvette motors, 5.7L 410hp
* Caddy Northstar motors.
* Lexus V8 VVTi Motors.
* Lamborghini V12s
* Torque V12s

All of these have proven to be NOVELTIES.

Claims have been made in this thread that "advanced" technology motors can be made to be reliable and put out 100hp/liter or better in a marine application.

Sure they can, at great cost.

Take, for example, a BMW 4.4 Liter V8 at around 420hp.
Nice damn motor. If I am staring at a 29' deep vee recreational hull and am choosing a motor, what do I need to consider?

Here's the answer: I need to consider TORQUE characteristics of the motors. I am NOT convinced that the BMW 4.4 (at 420horse tune) would be able to easily grunt the boat onto plane (at 2200rpm). I am NOT convinced that it would have adequate midspeed performance. AND I AM NOT CONVINCED IT WOULD PROVIDE 500 HOURS OF CONTINUOUSLY LOADED TROUBLE FREE PERFORMANCE IN A MARINE APPLICATION. I'm gonna choose a 496HO over the BMW motor and buy a spare to put in the shed and STILL save money. I don't expect that I would see any fuel economy benefit worth noting with either choice.

Also, when you get a chance, compare the fully-dressed weights of a BBC (with aluminum heads and intake, since you are comparing against an all aluminum BMW) with a 4.4 BMW. I promise you will be surprised.

In ALL honesty, we may be seeing the development of the perfect high performance marinemotors happening already, and in an environment FAR from Bavaria's Autobahn. BOATS HAVE DIFFERENT PERFORMANCE/TORQUE REQUIREMENTS THAN AN M5. Where, you ask, are these "perfect" marine motors being secretly developed???

Look on the ass of a new center console. Don't you see a big honking fourstroke? They are up to 250 horsepower now, and are climbing rapidly. I predict that if the market demands are strong for it, that these "developed for marine performance and environment" beauties will continue to get larger, and will be naturally altered to be rotated into a sterndrive configuration.

300 hp from 3 liters? No biggie.
400 hp from 4 liters. Sure.

Stop wishing. The future is near.

In the meantime, take a good look at what you get today for your dollar. The 496HO is a good example of good performance for he dollar, and good longevity, and excellent torque characteristics that fits the needs of boaters.

I'll put your magic Bimmer motor up against one any day, especially if you allow the score to be adjusted by "entry cost".
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Old 12-05-2003, 03:51 PM
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Thanks Mccollinstn, that was a good explanation of the difference between turbos and superchargers and it also explains why turbocharging is so effective on diesel engines. However, I would like to add one distinction within the family of superchargers. There are centrifugal superchargers and positive-displacement superchargers like the Lysholm screw type, Eaton, Roots... While it's true that the rotational speed of any type of supercharger will be related to the crankshaft speed, only positive-displacement superchargers will exhibit a linear boost-RPM relationship, ie. if you peak at 10psi at 6000 RPM, you will have 5psi at 3000 RPM. The centrifugal supercharger's boost-RPM relationship will depend on the configuration (mostly size) of driving pulleys and usually they are set to produce maximum boost at max RPM but you will have less than the relative max boost at lower RPMs. For example if you have 10psi at 6000 RPM again, you will have 3psi at 3000 RPM or something like that, instead of 5psi. Just a little distinction...

Concerning your comments about engines, I suppose you're talking about 4-stroke outboards and I agree 100% with you. But how is this any different from what I've been saying? Honda is the technology leader in this sector and they are an automotive company which is based on a strong engineering culture. They produce the highest specific output atmospheric engine on the market which is the S2000 motor, producing 120hp/liter. They also produce the highest revving production motor on the market, the Civic Sport which revs to 9200 RPM (at least in the Euro market). They are on the cutting edge as far as engine design is concerned. They were the first ones to try variable valve control and lift mechanism (V-TEC) and among the first ones to go to 4 and even 5 valves per cylinder. And they are applying this to their marine engines: aluminium blocks, DOHC, 4 valves per cylinder... And the results are impressive and include cleanliness, high performance and longevity. And this is exactly what I was talking about: application of modern technologies to marine engines to produce a better engine in every respect. BMW was just an example and you're right, perhaps Honda was a better one. Sure, they used to be insanely overpriced but have come down and have become affordable.

As far as the 496HO is concerned, I have to disagree. Under heavy load factors and continuous operation at 95%, such as when 4 are mounted on a 22 000 lb patrol boat, they last on average 50 hours. The only difference between a 502 and a 496 is that 496's electronics often stop you before major damage has been made so rebuilds are easier, whereas I used to see loads of fireworks with the 502... And I'm being kind by saying 50 hours...
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Old 12-05-2003, 03:56 PM
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BTW Mccollinstn, you're right about the main requirement for recreational boating: torque. But then a 496HO is far from being the best answer. Get a Yanmar diesel instead...
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Old 12-05-2003, 04:15 PM
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Quote:
Originally posted by super termoli
BTW Mccollinstn, you're right about the main requirement for recreational boating: torque. But then a 496HO is far from being the best answer. Get a Yanmar diesel instead...
Yea but they smell bad and sound worse

The main thrust of the Sterling/Torque program is industrial not marine.
 
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Old 12-05-2003, 04:24 PM
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FOR WHAT TYPE OF INDUSTRIAL APPLICATIONS??
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Old 12-05-2003, 04:32 PM
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The engine is being converted to NG and propane and will target power generation (standby) and perhaps bus/rv engines.
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Old 12-05-2003, 05:46 PM
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Termoli you are forgetting that the air flow capacity of the restriction after the blower (the engine) is closely related to RPM, not exactly linear but close, actually moves less air per revolution (therefore more restriction) as the RPM goes up. In my experience on the dyno assuming full throttle the boost does not change all that much from 2500 RPM up with a belt driven blower.
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