Question for you Detroit Guys

[67hat34c]

Moving this to the tech side.

I know very little about DD engines but was quite impressed with the 12v71 N that worked in Freebird. I know it is approx 485 hp but how much torque does this thing have?

From seeing the innards(redneck term) of the other one i have a better understanding of how the 2stroke diesel works, also saw an explanation on Yachtsurvey. Also noted how clean the internal parts of the dead engine were, expected some build up due to the nature of diesel oil but thata was clearly not the case.

 

[neosin]

When burning dinosaur bones in a 2 stroker DD "torque" doesn't really matter.

To all who's gonna tell me there is no such thing as horsepower there is only "torque" yes i know i build race engines... lol know all about it.

HOWEVER, it's a rating that better helps you understand what the engine does for you. The rule is "torque = gets you moving ; Horsepower keeps you moving"

The holds very true in boats, Really unless your gonna spend 90k in a repower to get 2kts more, you don't care about torque in a old hatteras yacht, what you need is horsepower to "keep you moving" at a given speed.

Most diesels make loads more torque than horsepower anyway, 300hp engines like a duramax in the truck makes around 600foot pounds of torque. I've seen a few 180hp diesels making 300 foot pounds of torque so it just depends on how the engines was built.

 

[Boatsb]

I guess all them enginerds is rong since there be no thing as Turque. I was thunking that the turque from them engines was a measure of work but since you knowed better I will leave it at that.

 

[krush]

The only thing that matters is HP. Tug boats are rated in HP, gensets are rated in power (kW, which is metric for HP), and turboshaft motors are rated in HP.

The only reason one worries about torque is to insure that the shafts are properly sized to handle the torque...HP does work, tork breaks stuff.

HP is the result of torque and RPM. To make an analogy, think of torque as current, RPM as voltage, and Power as Power (HP as watts, cuz it is the same thing).

/waiting for the discussion to start and to be told I'm wrong haha.


edit: and to appease the fundamentalists--torque is a force, HP is power (force*distance/time)

 

[MikeP]

Power is power. You can call it anything you want. A 435 HP gas engine produces the same amount of maximum power as a 435 HP DD. You can say that the DD produces more torque. But it doesn't really produce any more power it just produces it's power lower on the RPM scale and we commonly refer to power at the low end as torque. They will both make the boat move at the same speed (assuming we compensate for the weight difference of the engines.) The ONLY difference is that the gas engine will be turning a higher RPM to do the same thing.

An engine with 435 HP and 450 lb of torque won't produce a top speed any higher than an engine with 435 HP and 390 ft lb of torque.

But in a car, the 450 torque motor would make a much nicer street machine.

 

[Brian Degulis]

The only thing that matters is HP. Tug boats are rated in HP, gensets are rated in power (kW, which is metric for HP), and turboshaft motors are rated in HP.

The only reason one worries about torque is to insure that the shafts are properly sized to handle the torque...HP does work, tork breaks stuff.

HP is the result of torque and RPM. To make an analogy, think of torque as current, RPM as voltage, and Power as Power (HP as watts, cuz it is the same thing).

/waiting for the discussion to start and to be told I'm wrong haha.


edit: and to appease the fundamentalists--torque is a force, HP is power (force*distance/time)

Brian Degulis
Senior Member Join Date: Apr 2006
Posts: 269

Re: Looking at 56 Hat's 8V92's Problem??

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Props are always sized based on RPM Reduction Ratio and HP. Boats are driven by HP which is a total measurment of mechanical force very much like watts is a total measurement of electricity. RPM is similiar to volts and torque is similiar to amps. If you want to know the torque you can easily calculate it if you know the HP and RPM. Just like electricty if you know 2 of the values you can always calculate the third.


Frightening maybe your posts aren't so wacky?

Brian

 

[krush]

Frightening maybe your posts aren't so wacky?

Brian

Somebody that knows what they are talking about is always going to sound "wackier" than an eloquent bull$hitter. Also, I am a very sarcastic person, and sometimes the interweb doesn't transfer that tone

Glad we agree though!

On a side note, I forgot to add that boilers used to be rated in HP too. In the end, it's just a big units game.


edit: and I didn't copy your post....I never even read it till right now.

 

[spartonboat1]

Let me just say that one of those salties or Great Lakes carriers with a 300 rpm Pick... (shoot, I can't remember the engine mfg'rs name, its been 45 years since I changed the timing chain, which was the size of a fully mature Aaconda snake...took three of us to hold it up, whilst we fed it in).

Well, that 300 rpm (325 at WOT) is making some torque...and HP. Listening to those very large, slow turning commercial diesels sounds like a dozen munchkins, each trapped in a cast iron drum taking their turns tapping once every second or so.

 

[neosin]

I guess all them enginerds is rong since there be no thing as Turque. I was thunking that the turque from them engines was a measure of work but since you knowed better I will leave it at that.

lol did you read the post? i said horsepower; THE only thing an engine makes IS "turque". But you need the measurement of horsepower to.... ah never mind. I only know what it takes to run a 8.92 @ 150mph in the 1320... What do i know lol

 

[neosin]

Power is power. You can call it anything you want. A 435 HP gas engine produces the same amount of maximum power as a 435 HP DD. You can say that the DD produces more torque. But it doesn't really produce any more power it just produces it's power lower on the RPM scale and we commonly refer to power at the low end as torque. They will both make the boat move at the same speed (assuming we compensate for the weight difference of the engines.) The ONLY difference is that the gas engine will be turning a higher RPM to do the same thing.

An engine with 435 HP and 450 lb of torque won't produce a top speed any higher than an engine with 435 HP and 390 ft lb of torque.

But in a car, the 450 torque motor would make a much nicer street machine.

Yes, a 435 HP DD would be smaller than a 435 HP gas engine in theory if we went by cubes; because the diesel makes up for power in less cubes from the extra btu in diesel. However it wouldn't be hard to make a ford 302 make 435 hp (easy) with a LOT of weight savings over the diesel and it could be built to last. I don't dog gasoline engines just because mercruiser can't build a good engine, really you could build a gas engine with a low boost turbo that would last just as long or longer than a diesel. Gas engines can handle not being ran while your diesels hate it... mainly because of the rings used in DDs... but you could do the same thing with the DD if it was custom built which I've thought about doing one and seeing how well we could make it run... lots could be done with the heads alone in a 8v71N. The old DD 8v71 = 568 cubes (two stroke) could make anywhere up to about 1704hp in theory, and a long life DD 8v71N making 800-1000hp that would last 5000 hours or more isn't really hard to build i believe... only time will tell and i'm just the one crazy enugh to try it lol!

 

[Brian Degulis]

Somebody that knows what they are talking about is always going to sound "wackier" than an eloquent bull$hitter. Also, I am a very sarcastic person, and sometimes the interweb doesn't transfer that tone

Glad we agree though!

On a side note, I forgot to add that boilers used to be rated in HP too. In the end, it's just a big units game.


edit: and I didn't copy your post....I never even read it till right now.

I should have been a little more clear. I said you where wacky when I responded to your post on stablizers being only for old farts. I know you where kidding and so am I then and now. The thought that you copied my post never entered my mind I just thought it was kinda funny that we used almost the same analogy.

Brian

 

[krush]

Yes, a 435 HP DD would be smaller than a 435 HP gas engine in theory if we went by cubes; because the diesel makes up for power in less cubes from the extra btu in diesel. However it wouldn't be hard to make a ford 302 make 435 hp (easy) with a LOT of weight savings over the diesel and it could be built to last.

Compression ratio plays a big factor in it too. BTU content just determines the pounds per hour of fuel burnt. Higher compression ratio = more effcient. Slower RPM = more efficient. Less pumping losses due to no throttle = more efficient. Also, in diesel you don't have to worry about chasing that annoying problem called detonation.

And companies already make "gasoline" engines that do the same duties as diesel. The natural gas and propane engines cummins makes are basically converted over oil burners with spark plugs.

 

[MikeP]

1704HP from an 8V71? :EEK

The engine package would include flak jackets, right?

 

[Brian Degulis]

There's good reason why diesel's 2 stroke or 4 outlast gas engines it's the fundemental diffrence in operation. A gas engine compresses a fuel air mixture then a spark plug ignites it pretty much all at once so your firing pressure peaks at the time of ignition and then gets lower as the piston moves down. A diesel engine compresses only air then fuel is injected into the hot air and ignition begins but as the piston moves down injection continues so firing pressure stays more constant. Think of it as the diffrence between hitting the piston with a hammer or pushing it down with a press. The hammer will cause tremendous shock loads that will break things the press can impose a lot more energy without the stress.

This is why gas engines get only so big there's a point where firing pressures would peak so high the strain would simply be to much. Diesels on the other hand have no limit in size I think 95,000 HP is the high end today.

As far as an 871 producing 1700 HP Whoever knows how to do that should go ahead and do it and become very wealthy. More Hp from smaller engines is what every diesel engine manufacturer works toward and yet they are no where near that. If you can out smart all there engineers and get that much power from that size engine what are you waiting for?

Brian

 

[neosin]

1704HP from an 8V71? :EEK

The engine package would include flak jackets, right?

1704hp in THEORY... Theory being the key word, i'm sure it could be done... and run for... about 2 mins at an idle. LOL!

 

[neosin]

As far as an 871 producing 1700 HP Whoever knows how to do that should go ahead and do it and become very wealthy. More Hp from smaller engines is what every diesel engine manufacturer works toward and yet they are no where near that. If you can out smart all there engineers and get that much power from that size engine what are you waiting for?

Brian

IN THEORY! LOL Now days, ram enough air down the throat and be able to control it's combustion you can make a lot of power out of small cubes. Might not last long but hey...

However if you believe DD, MTU, Cat, mercuiser, etc are building engines that are engineered to be the best they can be your out of your mind. They work on the idea of "something to sell ya later" lol. ever wondered why they can't make a 350 - 450 hp diesel that lasts and is cheap by now? I mean with all the improvements and tech and robots building everything, no cheap diesel re-power?

An engine is just one thing. AIR PUMP, nothing more. The better it can pump air the more power it makes. There is many "types" of air pumps we'll call engines. LOL

The real main difference in a true diesel and gas engine is that a gas engine is a controlled combustion air pump and a diesel is a compression combustion control air pump. A diesel doesn't use a throttle like your used to on gas engines, but rather it's always full throttle and your only controlling the fuel that goes into it, thus making more power as more fuel is poured in. In my book anything other is not a "true" diesel. Out of the box better air pump lol

In theory a DD 8v71 would continue to make more power until the point the crank can't handle the weight, not very well balanced, etc and throws a rod. If you was to use better pistons (lighter, stronger) Better rods (lighter stronger), a little head work to flow better, and built a real crank for it (lighter, stronger, far better balance) you could make a lot more power out of the same cubes.

The better balance itself would give you another 1000 rpms easy. Remember this, @ 45%ish of your total engine Efficiency is being eatin' up by vibration in the internals. Lower this 15% and what do you get? Not that hard to do on the cheap if you know someone with a machine shop and is willing to let you use it...

Almost everything internal is "floating" on oil, cams, crank, rods, pistons, etc.. etc.. That slight gap takes up the vibration, then you have the shaft, etc.. on and on Remove that vibration ... even the stuff you "don't" feel and you'll gain a lot of "Efficiency" that is already coming out of your engine but your just losing. Point here is this, you are losing a lot just from balance alone right now. Go right now and have just your props rebalanced and you'll gain some, do the shaft, then the tranny, then the crank, i'd bet you'd pick up 20%-25% right there if not a lot more. I know the cranks on these things are just junk to start with... something to be said about an engine that only turns 2350 to begin with.

Yes i know low rpm reduces wear, for you i say look up amsoil and find out how you can pick up 10% Efficiency right now... Reduce the friction, and pick up rpms without extra wear. This isn't brain science guys i'm just putting out there what i know from racing.

How about a 454 punched .060 over turning 8500 rpm? Your normal big blocks only turn half that. All we do is work out the balance, lighter pistons, rods, crank, etc.

We do this all the time in race engines, even the smallest balance fix will get you another 100rpm, etc when your spinning 8000rpm out of a .060 over bigblock 454 you'd better have your balance right or your just making paper weights.

Anyway, My point is this, You can make internals lighter with better balance for better torque making monster then add yourself a nice heavy flywheel and you'll have one awesome running DD! Make the airpump more efficient = more power. You don't "need" more cubes. There is no reason a 500+ cube DD isn't making 600hp and lasting decades.

You guys just give them thar engenears to darn much credits. mabe why theys dont have elcetrick kars by now becaurs we's just can't make betta batteries? ya! right. If you buy that, i've got a bridge over here for sale...

Have fun guys!

DISCLAIMER
Any of you guys go out and try to "balance" your crank and kill your engine it's YOUR FAULT! not mine! hahah We spend MONTHS working the math on a new crank...

 

[DavidK]

Diesels on the other hand have no limit in size I think 95,000 HP is the high end today.

Brian

Actually, the high end today is another 2 CYCLE diesel. The Wartsila-Sulzer RTA96-C turbocharged two-stroke diesel engine.... (as Tim Allen would say "ar, ar, ar"). In addition to

Maximum power: 108,920 hp at 102 rpm
Maximum torque: 5,608,312 lb/ft at 102rpm

at over 50% thermal efficiency, its also one of the most efficient engines in the world.


http://people.bath.ac.uk/ccsshb/12cyl/

 

[MikeP]

I don't think anyone doubts the fact that you COULD produce 1700HP from an engine configured LIKE an 8V71. But it wouldn't be a DD 8v anymore because every part in it would be different. It's kind of like saying that all top fuelers use Mopar Hemi's to produce their 5000+ HP. Yes, the engines are BASED on the Mopar hemi design but that's it.

Heck, formula one cars currently use 183 CID, naturally aspirated engines that weigh around 200 lbs and produce 800+ HP. But you could stick 4 of 'em in there, have 3200HP and weigh less than a third of what ONE dd weighs and they would occupy less space! Of course they spin 19000+ RPM to produce that power which might be a bit "buzzy" in a boat!

Based on my experience with building gas engines (though NONE with diesels) I'd expect to see 20 percent more power and efficiency in a DD if you just blueprinted it. This, frankly, seems to me to be about the limit in what is reasonable for these old motors. Going beyond this means essentially redesigning the thing.

 

[krush]

How about a 454 punched .060 over turning 8500 rpm? Your normal big blocks only turn half that. All we do is work out the balance, lighter pistons, rods, crank, etc.

We do this all the time in race engines, even the smallest balance fix will get you another 100rpm, etc when your spinning 8000rpm out of a .060 over bigblock 454 you'd better have your balance right or your just making paper weights. .

That's nice, but one must note that RPM is the killer of efficiency. Power output on engines is close to linear, but the losses due to friction are exponential. This is one reason the low RPM ship engines (150rpm max) get close to that 50% thermal efficiency.

Making lots of power is one thing; making lots of power efficiently is another. A turbo shaft can make a ton of power and weighs very little but it's low compression ratio gobbles fuel.

 

[67hat34c]

Guys, I only wanted to know how much torque the 12v71 in the bird produce.