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!