Common misconceptions

[J_Ashley]

About the Briggs vs. the Yanmar diesel engines. Briggs, as well as many other small engine manufacturers do not measure power output for their engines on a dynamometer. They instead are simply calculated based on cylinder bore/stroke, compression ratio, air/fuel ratios, volumetric effiecency and rpm all as factors. I'm not sure about the Yanmar diesels. As stupid as it sounds, it's really not a fair comparison.

And about the I6-V8 argument (one i'm kind of tired of). Given similar displacment, the reason an I6 engine is prone to higher Torque production, and likewise V8's are prone to higher HP production, has to do with designs.

We'll use the Ford 300ci I6, and 302Ci V8 as examples. These two engines are close in displacment, however, the I6 has a greater displacment per cylinder. This means that the bore and/or stroke must be larger to make similar total displacment. Between the two engines, the I6 has a longer stroke. The longer stroke means that the crankshaft has a longer distance between its journals. As the crankshaft rotates so that the journals are horizontal to eachother (piston is half-way between TDC and BDC) the piston is applying more leverage to the crankshaft. In a shorter-stroked V8, there is less leverage now, meaning less torque. This effect is most noticable at low RPM's.

However at higher RPM's the V8 will start to produce more HP. Given the shorter stroke, the engine is more comfortable that the bulkier I6 in the high revs. As a result, the engine will probably rev higher, and therefore will make more HP.

Justin

 

[MacDaddy]

Ok how about this one why does a v style motorcycle motor have more torque than a inline motorcycle motor That just puts the inline to v style theory out the window Bottom line is a 300hp longer stroke motor with longer rods will have more torque than the same cubic inch motor with 300hp and a short stroke and short rods But in a drag race the short stroke motor will win But on a hill with a load the long stroke motor will win Go to Falicon .com they have some good info about stroke and rod length

 

[MotoBoyMatt]

I know a normally aspirated Winston Cup NASCAR engine with a restrictor plate in the intake will put out ~780 HP all day at 200+ MPH. A 6.0L Winston engine weighs about 500 pounds.

Now, a question for you:
How much would a normally aspirated diesel weigh to put in an automobile and push 200 MPH?

Yeah you can do anything with enough money, what does a NASCAR engine cost? about $20,000 and it's good for what? 500 miles.

 

[pbtree]

How about a rotary?

 

[PWB]

Now, a question for you:
How much would a normally aspirated diesel weigh to put in an automobile and push 200 MPH?

Try cumminsracing.com

8 second 6 cyl. cummins rail

 

[MotoBoyMatt]

HP is therefore equal to Torque, times the RPMs, all divided by 5252. < HP = ((Tq. x RPM) / 5252) > When you look at a Dynograph, at 5252 RPM, Torque and Horsepower will ALWAYS be equal. Below 5252 RPM, Torque will ALWAYS be greater than Horsepower. Above 5252 RPM, Torque will ALWAYS be less than Horsepower.

When you look at a diesel engine for example, they make typically 2-3 times more Tq than HP. This is because they make an abundace of torque (Force that does the work) at relatively low RPMs, and don't need to rev high to make what would be useless HP. This is why low-revving diesel engines, are suited for truck use.

Justin

Why do you say that the high reving HP is useless? Torque being lower than HP above 5252 RPM's doesn't really mean anything. 5252 is no magic number it's just where the two curves intersect, if you used different units the RPM at which the curves meet would be different.

 

[1Alpha1]

A few years ago, I had heard that Catepillar was hurting financially, and was laying off employees right and left.

I had also heard that Ford was trying to make a deal with Cat to have them supply a power plant for their pick-ups.

Haven't heard a single thing since..........

 

[BlueRidgeMark]

HP is therefore equal to Torque, times the RPMs, all divided by 5252. < HP = ((Tq. x RPM) / 5252) > When you look at a Dynograph, at 5252 RPM, Torque and Horsepower will ALWAYS be equal. Below 5252 RPM, Torque will ALWAYS be greater than Horsepower. Above 5252 RPM, Torque will ALWAYS be less than Horsepower.

Justin, I think you have a misconception there. OR perhaps you are minxing up two different things. Where the horsepower curve and torque curves intersect will be diffferent for every engine. Each is affected by many different design factors, SOME of which are bore, stroke, intake paths, exhaust paths, etc. Change any one of them and you'll change both curves, AND their intersection point. For a given engine, if you plot those curves 20 different times you'll get 20 different curves, with 20 different intersection points. They won't differ by MUCH, but they won't be EXACTLY the same, either. OR, take 20 different engines, each having exactly the same design, and plot the curves of each, and you'll get 20 different curves, with 20 different intersection points. They won't differ by MUCH, but they won't be EXACTLY the same, either.

Now change the headers and your curves will be VERY different, as will your intersection point. Change the timing and your curves change again.

Plot a saw motor vs. an Allison deisel and the curves AND intersection points will be RADICALLY different. Plot a Suzuki 1000cc bike motor vs. a tanker ship's diesel, and again, radical differences.

Simple rule of thumb:

Longer stroke = more torque.* This is why v-Twins have more torque than a 4 cyllinder inline of equal displacement. It's not because it's a V, and it's not because it's a twin, and it's not because Harley invented it. It's because they typically have longer strokes than the equivalent 4 cylider. You could easily make an inline 4 with more torque than any Harley, but you'd wind up with an engine that's too tall for a motorcycle. When you go to the V configuration, you reduce the overall height of the engine.



* This is a generalization - there are other factors. But, all other things being equal, it holds true.

 

[BlueRidgeMark]

Which weighs more, a lb. of feathers or a lb. of lead?

I think those are the same.


But a pound of lead is NOT the same as a pound of gold!

(Or silver.)

 

[BlueRidgeMark]

Okay, okay, enough of this quibbling! Let's settle this!


THIS IS TORQUE:

(All 5.6 million foot pounds of it!)



And THIS is horsepower!

That flame you see from the exhaust stacks of funny cars? That's not unburned fuel. That's burning hydrogen. It comes from water vapor in the air. When the exhaust exits the stacks, it's so hot it breaks down water vapor in the air, turning it into hydrogen & oxygen. The hydrogen promptly burns, which is what you see as flames which appear to be shooting out of the exhaust stacks.

Any questions?

 

[neverenough]

Justin, I think you have a misconception there. OR perhaps you are minxing up two different things. Where the horsepower curve and torque curves intersect will be diffferent for every engine. Each is affected by many different design factors, SOME of which are bore, stroke, intake paths, exhaust paths, etc. Change any one of them and you'll change both curves, AND their intersection point. For a given engine, if you plot those curves 20 different times you'll get 20 different curves, with 20 different intersection points. They won't differ by MUCH, but they won't be EXACTLY the same, either. OR, take 20 different engines, each having exactly the same design, and plot the curves of each, and you'll get 20 different curves, with 20 different intersection points. They won't differ by MUCH, but they won't be EXACTLY the same, either.

Now change the headers and your curves will be VERY different, as will your intersection point. Change the timing and your curves change again.

Plot a saw motor vs. an Allison deisel and the curves AND intersection points will be RADICALLY different. Plot a Suzuki 1000cc bike motor vs. a tanker ship's diesel, and again, radical differences.

Simple rule of thumb:

Longer stroke = more torque.* This is why v-Twins have more torque than a 4 cyllinder inline of equal displacement. It's not because it's a V, and it's not because it's a twin, and it's not because Harley invented it. It's because they typically have longer strokes than the equivalent 4 cylider. You could easily make an inline 4 with more torque than any Harley, but you'd wind up with an engine that's too tall for a motorcycle. When you go to the V configuration, you reduce the overall height of the engine.



* This is a generalization - there are other factors. But, all other things being equal, it holds true.

Amazing, you are wrong on everything you posted.

Yes, HP and torque have the same numerical value at 5252 on EVERY 4 stroke motor. Period! I don't understand your plottiing theory, but, oh well.

As far as the stroke equals torque theory, yeah, is sounds good, and some motors are designed poorly, and the longer stroke helps to over come that, but the only time torque is directly effected by the stroke is in a properly "stroked" motor. Taking a Ford 460 and making it into a 521 will increase low rpm torque, all other things remaining the same. But to say a longer stroked motor makes more torque than a shorter stroked motor of the same displacement is totally false. It depends on the design of the motor. I've seen it on the dyno, then proven in use. 2 makers, EXACT same displacement, and the motor with the nearly square motor stomped all over the motor with the longer stroke. The square motor had a very broad torque band, being 1.23 percent lower on peak torque than the long stroke.

 

[belgian]

 

[jokers]

Amazing, you are wrong on everything you posted.

.....But to say a longer stroked motor makes more torque than a shorter stroked motor of the same displacement is totally false. It depends on the design of the motor.

neverenough, weren`t you ever told to never speak in absolutes such as "totally false"? Anyway, your statement makes it clear that the "design of the motor" is what causes the difference in torque between two motors of equal displacement but having different bore/stroke relationships, and that long stroke doesn`t always equate to higher ultimate torque. By your use of the word "design" you clearly imply that the bore/stroke ratio is not the design you are speaking of, but more likely you are referring to design features which increase the efficiency of a higher torque, shorter stroke, equivalent displacement engine. Am I correct?

Assuming that I understand your first statement, then doesn`t this second statement by you from the original post refute what you just said in the first statement?

I've seen it on the dyno, then proven in use. 2 makers, EXACT same displacement, and the motor with the nearly square motor stomped all over the motor with the longer stroke. The square motor had a very broad torque band, being 1.23 percent lower on peak torque than the long stroke.

Just wondering, because your statement makes it seem that the square motor was capable of much higher performance(assuming that you mean horsepower) or efficiency, yet it`s peak torque did not match that of the long stroke, lower efficiency motor. Could you please clarify?

Russ

 

[Simonizer]

Why do you say that the high reving HP is useless? Torque being lower than HP above 5252 RPM's doesn't really mean anything. 5252 is no magic number it's just where the two curves intersect, if you used different units the RPM at which the curves meet would be different.

5252 is indeed not a magic mumber.

H.P.= 2*PI*n*t/33000; n=RPM, t=Torque in lbs*ft

Therefor t=(H.P)*33000/2*PI*n; the constant 33000/2*PI is 5252.11.

no magic here. Elementary my dear Watsons.

 

[Simonizer]

So your point is that 33000 IS the magic number?

No, 1 horsepower is 550 ft*lbs per second, or 33000 ft*lbs per minute. Since we are using revolutions per minute to define angular velocity, we must use ft*lbs per minute to keep the units correct.

 

[Simonizer]

Did anyone know that some electric motors develop their highest torque @ 0 Rpm's? Plug that in you HP formula.

This "plugs" into the formula perfectly. If it is not turning, it is doing zero work, therefor developing zero horsepower.

 

[BlueRidgeMark]

Amazing, you are wrong on everything you posted.

Yes, HP and torque have the same numerical value at 5252 on EVERY 4 stroke motor. Period!

Yep, I was wrong on that. Too long since I've messed with motors.

I don't understand your plottiing theory, but, oh well.

You don't understand plotting horsepower & torque curves?

Here. maybe Mr. Banks can help you.

http://www.getpower.com/Banks_FridayNight_010402.cfm

As far as the stroke equals torque theory, yeah, is sounds good, and some motors are designed poorly, and the longer stroke helps to over come that, but the only time torque is directly effected

That should be "affected". http://www.precisionproofreading.com/affecteffect.htm

by the stroke is in a properly "stroked" motor. Taking a Ford 460 and making it into a 521 will increase low rpm torque, all other things remaining the same.

Yes, that's what I said. "All other things being equal" a longer stroke motor will produce more torque. Of course you can get a square motor, or even an over-square motor, to produce more torque than an undersquare motor of the same displacement by changing other design considerations.

Duh.

Still, in general, longer stroke motors produce more torque than short stroke motors. Uh, that might be why big truck engines are typically long stroke motors! Wow!

 

[J_Ashley]

BlueRidgeMark, if you read my second post, you'd have seen my argument for engine strokes and such. And yes, HP and Tq are ALWAYS Equal at 5252 RPM. It's a function of math, not a product of engineering.

Bottom line is this -> The quantity of Torque will determine the capacity to perform work. HP is a reflection of how fast said work will be done.

Justin

 

[chowdozer]

Try cumminsracing.com

8 second 6 cyl. cummins rail

Ahh, yes...

You read my question, but obviously didn't answer it?

How much would a normally aspirated diesel weigh to put in an automobile and push 200 MPH?

So you answer with a link to a dragster with a forcefed Cummins that makes it to 167 MPH for a split second.

 

[chowdozer]

Yeah you can do anything with enough money, what does a NASCAR engine cost? about $20,000 and it's good for what? 500 miles.

I was merely pointing out that diesels aren't the answer for everything. If you didn't read the last two lines of my post, you have the oppurtunity to read them now, as I will retype them.

Horses for courses.
I'm glad my saws aren't diesel.