How much torque do the piston engines make...

[Wankel7]

I have always wondered what the torque rating is on the horizontally opposed engines. Such as the IO-540 and what not.

Has anybody ever seen those figures published?

Wankel

 

[vetteracer]

BHP is "brake horsepower" and is derived from the fact that torque/power is usually measured on a dynamometer with a "brake" to place a load on the engine, so torque can be measured. Then horsepower is computed from the formula T x N/5252, where T is torque in lb-ft and N is RPM. "Brake horsepower" is used interchangeably with just "horsepower", but it can be measured using different types of equipment.

The current industry accepted SAE 1349 standard requires that engine power be rated at the flywheel "as installed", which includes all normal accessories and the production exhaust system. Observed readings are then corrected to 990 millibars (29.335" Hg.) and 25 degrees C (77F) dry air. (Duke Williams)


Torque is a centrifugal calculation and HP is a linear calculation. They are representative of each other.

Here is the basic formulas

Horse Power = TORQUE * RPM / 5252

Torque = HP * 5252 / RPM

So a TSIO-520, rated at 300 HP at 2700 RPM and full manifold pressure.

Torque = HP[300] X 5252 / RPM[2700]

Torque = 300 X 5252 / 2700

Torque at 2700 RPM = 583 ft. pounds.

 

[Wankel7]

Man, thanks for laying it out like that. That is one torquey engine

Wankel

 

[vetteracer]

You’re welcome.

Horsepower gets its fame from marketing hype and the racing venue. In any engine designed for applications such as over the road trucks, RV’s, every day cars, piston airplanes, etc, torque and the torque curve is were it is at. Torque across a broad rpm and power range is key. This way you do not have an engine that makes all of its power at some small RPM range.

A good example is my corvette. It has a very high horse power rating, but the torque curve is horrible. There is not enough torque below 3000 RPM to do anything were high performance is concerned, but, at 4500 RPM and up it is a rocket. So the application would be impractical in every day use, pulling a trailer, etc.

Running max takeoff power is not practical and a more non-offensive setting is needed in cruise flight. If you had an engine with a very steep torque curve, versus a flat curve, you would have an engine that would fall on its face where power is concerned when you set cruise power. So a 500 HP motor with a peaky torque curve would be less beneficial then a 300 HP motor that made all kinds of torque across a broad range. The 500 HP would be great for takeoff, but nothing else.

High RPM and low manifold pressure are very hard on these types of engines. The force on the propeller from the ram air over powers the engine and the prop begins to drive the crank, instead of the crank driving the prop. This causes the pistons to "flutter" and can be very hard on the piston rings.

On the other spectrum, you have low RPM setting with Max manifold pressure. This is not as harmful as the other scenario, but it should be tolerated for takeoff only. There are provisions for this on Turbo charged aircraft that allow you to run over squared. This situation created high load and low RPM. With High RPM (with in reason) you have centrifugal stability and rigidity in the rotating crank and piston. When the rotation slows down, and power is increased, load can overcome the rotating stability and cause piston slap. This can also cause "PINGING" or pre-detonation. The Avgas we use prevents most of this due to the high octane.

Probably a lot more then you care to hear, but it is Sunday and I am bored.

Mark

 

[Bus Driver]

Vetteracer,
Thanks for the post, I’ve seen the TxN/5252 formula before and wondered about the 5252 constant. Or more specifically how does the SAE remove the time factor from the HP/torque constant of 1HP=33,000 ft.lbs/minute. Using this my 270 HP ‘71 corvette produces 8,910,000 ft.lbs/minute instead of the 360 ft.lbs. on the console placard.


P = indicated average effective pressure on one piston. or BMEP for BHP
L = Length of stroke in feet
A = Area of a single piston head in inches
N = Number of power strokes per minute, per cylinder, or RPM divided by 2
K = number of cylinders

PLANK/33,000=HP

Thanks

 

[vetteracer]

I got a gratuitous "C" in Thermal Dynamic but If I remember, any engine with the PLANK rules and other constants will produce the same power regardless of displacement, only the smaller engine will have to REV much higher to make the same power as the larger displaced engine.

Is your 71 an LT-1 ?

 

[Bus Driver]

Is your 71 an LT-1 ?

I wish! No it's the little 270 hp 350.

 

[sstearns2]

Vetteracer,

Torque has nothing to do with how a car or an airplane performs. Look at the car/airplane performance equations. It's all horsepower. Torque is simply a reflection of what RPM the horsepower is being made at. A 'high torque' engine is simply one that puts out a lot of horsepower at a low rpm.

Scott

ps- had a 77 and an 89 corvette, now a happy Integra GS-R owner.

You’re welcome.

Horsepower gets its fame from marketing hype and the racing venue. In any engine designed for applications such as over the road trucks, RV’s, every day cars, piston airplanes, etc, torque and the torque curve is were it is at. Torque across a broad rpm and power range is key. This way you do not have an engine that makes all of its power at some small RPM range.

A good example is my corvette. It has a very high horse power rating, but the torque curve is horrible. There is not enough torque below 3000 RPM to do anything were high performance is concerned, but, at 4500 RPM and up it is a rocket. So the application would be impractical in every day use, pulling a trailer, etc.

Running max takeoff power is not practical and a more non-offensive setting is needed in cruise flight. If you had an engine with a very steep torque curve, versus a flat curve, you would have an engine that would fall on its face where power is concerned when you set cruise power. So a 500 HP motor with a peaky torque curve would be less beneficial then a 300 HP motor that made all kinds of torque across a broad range. The 500 HP would be great for takeoff, but nothing else.

High RPM and low manifold pressure are very hard on these types of engines. The force on the propeller from the ram air over powers the engine and the prop begins to drive the crank, instead of the crank driving the prop. This causes the pistons to "flutter" and can be very hard on the piston rings.

On the other spectrum, you have low RPM setting with Max manifold pressure. This is not as harmful as the other scenario, but it should be tolerated for takeoff only. There are provisions for this on Turbo charged aircraft that allow you to run over squared. This situation created high load and low RPM. With High RPM (with in reason) you have centrifugal stability and rigidity in the rotating crank and piston. When the rotation slows down, and power is increased, load can overcome the rotating stability and cause piston slap. This can also cause "PINGING" or pre-detonation. The Avgas we use prevents most of this due to the high octane.

Probably a lot more then you care to hear, but it is Sunday and I am bored.

Mark

 

[Tripower455]

now a happy Integra GS-R owner.

That explains your interpretation of the torque vs horsepower discussion.......

FWIW, despite fact and proof, most "sport compact" owners think the same thing........

 

[A Squared]

Vetteracer,
Thanks for the post, I’ve seen the TxN/5252 formula before and wondered about the 5252 constant. Or more specifically how does the SAE remove the time factor from the HP/torque constant of 1HP=33,000 ft.lbs/minute.
Thanks

Bus driver: they haven't removed the time element, it's still there, remember N means RPM and obviously RPM (revolutions per *minute*) has a time element.

The reason you are getting confused by the two different formulas for HP is because there are 2 different kinds of foot-pounds.

A foot-pound can be a unit of work, or it can be a unit of torque. The work unit has nothing at all to do with the torque unit, it is merely a confusing accident that they have the same name. Recently there has been an attempt to reduce this confusion by referring to torque units as pound-feet, but not everyone has adopted this convention so the confusion persists.

Here's a brief explanation of the two different foot-pounds:

Work: Work is ameasure of a force applied over a distance. If you have a box that takes one pound of force to move, and you move it one foot, you have done one foot-pound of work.

That is the foot-pound referred to in the formula 1 Hp =33,000 ft-lb/min. What this means is that in order to move that box 33,000 feet in one minute, or move a box, which takes 33,000 pounds to move, one foot in one minute will require one Horsepower. Horsepower is the rate of doing work. Now, notice that the discussion of this type of foot-pound has no mention of turning or twisting?, Just a force moved over a distance.


Torque. The other foot-pound is a unit of torque. Torque is a measure of twisting force. If you have a wrench one foot long, and you put it on a bolt and push on the end with one pound of force, that is a foot-pound of torque. You do not have to move the bolt, because torque is a force only, nothing has to move, as it does in *work*

Now if you take this torque *force* and combine it with rotation, you have work, (force and motion) and if you combine it with rotational speed (RPM) you have power (force, motion, and time) That's how you can get horsepower from torque and RPM

That's why HP= 33,000 ft-lb/minute and HP= FT-lb*RPM/5252 are so different, it's because the ft-lb in one is not the same as the ft.-lb in the other.

Does this help, or have I just further confused you and/or put you to sleep?

 

[vetteracer]

QUOTE
Torque has nothing to do with how a car or an airplane performs. Look at the car/airplane performance equations. It's all horsepower. Torque is simply a reflection of what RPM the horsepower is being made at. A 'high torque' engine is simply one that puts out a lot of horsepower at a low rpm.
Scott
ps- had a 77 and an 89 corvette, now a happy Integra GS-R owner.


Torque has nothing to do with how a car or an airplane performs\

OK, I checked this out, and this is the response I found.


Power is a "dynamic" measurement - energy per unit time. To increase the speed of a vehicle we have to add kinetic energy. This is done by applying a force for a period of time, and the relationship to acceleration is Newton's Second Law, F=ma. On a car it's the drive thrust at the wheels that provides the force required to accelerate it, and on an airplane it's the propellor or exhaust thrust of a jet engine. The higher the energy per unit time we input (power) the faster the vehicle will gain speed. (accelerate).


The same applies to overcoming drag force at a steady speed. On a car there are two major drag components - aero and rolling resistance. Aero drag is proportional to the square of velocity and rolling resistance is a linear function of velocity. Due to the square relationship, aero drag is the dominant factor at high speed.

At a steady speed drag is a force, not a "dynamic" property.. The key is that the drag energy dissipated per unit time is proportional to velocity.

Drag Power = Velocity times drag force, and since we know the formula for engine power is T x N/5252 we can equate the two at steady speed.

Drag force x velocity = T x N/5252

Any power that the engine produces in exceed of the requirement to overcome drag is available to accelerate the vehicle by applying a force over time at the rear wheels.

One of the advantages of a large displacement engine like Corvette engines is their torque. The high torque means that high power is available at relatively low revs and average power across the operating range is higher than on a small displacement high revving engine of the same power output. If you ever drive a Ferrari F355/360 you will find out very fast that it will barely get out of it's own way below 4000 revs.


In my discussions of engine output I always emphasize torque bandwidth, and the 80 percent bandwidth is a good representation of engine elasticity. If the 80 percent torque bandwidth begins at low revs, it means the engine will be responsive right off idle - you don't have to wait for it to spool up to higher revs before it really begins to pull. A high torque bandwidth engine feels very linear in it's power output (linear with respect to revs).

The following are typical 80 percent torque bandwidths for a variety of engines.

Medium perf. vintage Corvette engine such at the 327/300 : 1500-5000
Special High Performance Corvette/FI vintage Corvette engine: 2000-6000+
Ferrari F355/360: 4000-8500
New Corvette LS2: 1200-6500

Notice that the LS2 bottom end of the 80 percent torque bandwidth is similar to the vintage medium performance engine, but the top end is similar to a vintage SHP engine, which is the best of both worlds. Duke

Mark

 

[Kingairrick]

Vette is correct. Horsepower ratings are almost always derived from the torque using the above formula. Ever seen a turboprop with horsepower guages?

Foot pounds are an exact unit of measurement, (feet, pounds) Horsepower was invented by marketing people to help sell cars.

Perfect example is the Honda s2000: 240 horsepower, AT 9000 RPM = no torque or crappy accelleration. Large deisel truck, only 300-400 horsepower but runs at around 1700 RPM=LOTS of torque, can pull your house...

It's all about the torque, baby...

 

[gfvalvo]

Perfect example is the Honda s2000: 240 horsepower, AT 9000 RPM = no torque or crappy accelleration. Large deisel truck, only 300-400 horsepower but runs at around 1700 RPM=LOTS of torque, can pull your house...

As an aside, the truck's accelleration will also be quite crappy while pulling your house.

Greg

 

[gfvalvo]

A foot-pound can be a unit of work, or it can be a unit of torque. The work unit has nothing at all to do with the torque unit, it is merely a confusing accident that they have the same name. Recently there has been an attempt to reduce this confusion by referring to torque units as pound-feet, but not everyone has adopted this convention so the confusion persists.

Here's a brief explanation of the two different foot-pounds:

Work: Work is ameasure of a force applied over a distance. If you have a box that takes one pound of force to move, and you move it one foot, you have done one foot-pound of work.

That is the foot-pound referred to in the formula 1 Hp =33,000 ft-lb/min. What this means is that in order to move that box 33,000 feet in one minute, or move a box, which takes 33,000 pounds to move, one foot in one minute will require one Horsepower. Horsepower is the rate of doing work. Now, notice that the discussion of this type of foot-pound has no mention of turning or twisting?, Just a force moved over a distance.


Torque. The other foot-pound is a unit of torque. Torque is a measure of twisting force. If you have a wrench one foot long, and you put it on a bolt and push on the end with one pound of force, that is a foot-pound of torque. You do not have to move the bolt, because torque is a force only, nothing has to move, as it does in *work*

Now if you take this torque *force* and combine it with rotation, you have work, (force and motion) and if you combine it with rotational speed (RPM) you have power (force, motion, and time) That's how you can get horsepower from torque and RPM

That's why HP= 33,000 ft-lb/minute and HP= FT-lb*RPM/5252 are so different, it's because the ft-lb in one is not the same as the ft.-lb in the other.

Does this help, or have I just further confused you and/or put you to sleep?

Nice explanation, let's carry it a bit further.



Push on the wrench with 1 pound of force until you make a complete revolution. You will then have applied a force of one pound over a distance equal to the circumference of a one foot radius circle (C = 2 *r* pi = 6.283 ft). Since

work = force X distance, you will have done 6.283 ft-pounds of WORK. If it took you 1 minute to complete the turn, your POWER output during this minute will be

POWER = work / time = 6.283 ft-pounds / minute.

Since 1 HP = 33,000 ft-pounds / minute, you will have produced 0.0001904 HP during this time. If the wrench were 2 feet long, the required force would be cut in half but the distance traveled would be doubled. Thus the work and HP would remain the same.



Now figure it using torque and RPM: A force of 1 pound applied at a distance of 1 foot produces a torque ("twisting force") of 1 foot-pound on the bolt. If you make 1 complete revolution in 1 minute, that's 1 RPM. So

HP = ft-lb * RPM / 5252 = 1 * 1 / 5252 = 0.0001904 HP !!!!



Hot Darn, it works out to the same number when figured either way -- as it must.



How's THAT for using my college degree in an aviation application? (Granted, anybody who passed high school physics could have figured this one)



Greg

 

[A Squared]

Torque vs. HP

Thanks to GFValvo for adding "the rest of the story" to my explanation.



You folks beating the "torque is king" drum don't quite grasp the physics of the matter. You really don't. It's that simple.

No, I'm not going to get into your silly "big displacement American engines are better than high-revving foreign engines" argument because quite frankly it's that emotional mindset which is leading you do rationalize your preferences with inaccurate statements.

Yes, I do understand your position that an engine with a nice fat power band is a lot more driveable than one with a narrow one. No, it's not torque, it's *power*. Anytime you talk about torque at such and such RPM, you're not talking about torque at all, you're talking about power. Ask any high school physics teacher.

"It's all about the torque, baby..."

This quote seems to sum up the position of several of you. Let's take that statement at face value, let's say that it *is* all about the torque. OK, what's an impressive amount of torque? Anyone? 500 ft-lb? Is that enough to make everyone go oooooooooooOOOOOOOHhhhhhhhhhh!!!!!!!!!!!?????
OK 500 ft-lb. is a lot of torque, and "torque is what it's all about .... baby", right? So if we had a powerplant which developed *twice* that torque, and dropped it in Vetteracer's Corvette we'd have one screaming Mo-chine, wouldn't we?

OK, I'll give you a 1000 ft-lb. powerplant. I'll take a Briggs and Stratton lawnmower engine which develops 5 hp at 3000 rpm. (stock, not one of those hotrodded ones in the kiddy dragsters) I'll slap a 1:115 gear reduction unit on it and; Viola!!! 1000+ ft-lb. of torque. (ignoring friction losses in the reduction unit) Drop that baby into a Vette and you'll really burn the tires, right?

But wait, you say, that shaft is turning really slow, like 26 rpm ... Ummm yeah? So???, You said "It's all about the Torque........."baby"! And I've given you torque, Specifically, you want low end torque? Right? Hey it's hard to get a low end lower than 26 RPM, and 1000 ft-lb of torque, woweeeee!!!!!!

"Noooo, nooooo" you say, "we need torque at XXXX RPM". Nope, sorry! As soon as you throw RPM in there, you're talking about power, not torque. That's just physics. You may *think* you're talking about torque, you may really, REALLY believe you're talking about torque, but you're not, you're talking about power. Like I said before, ask any physics teacher, this is basic, day one high school physics. There is no RPM in torque, and I've just given you *LOTS * of torque.

So, why aren't Corvettes all powered by 5hp. Briggs and Stratton lawnmower engines equipped with gear reduction units? It's because a lawnmower engine doesn't have the *power* to make a Corvette perform like a Corvette should.



"Foot pounds are an exact unit of measurement, (feet, pounds) Horsepower was invented by marketing people to help sell cars."

Sorry Rick, but this is without question the most ignorant statement in this entire thread (possibly the most ignorant statement this week on the entire forum, but I digress) Horsepower, (and the metric unit of power, the "watt") has been around much, much, longer than automobiles have been around. The horsepower is indeed an exact unit of measurement, as is the watt. Power is a very specific, well defined quantity. The fact that you obviously don't understand it, doesn't mean that it doesn't exist.

"Ever seen a turboprop with horsepower guages (sic)?"

2 reasons for that, neither of which support your point:

1) Torque developed by an engine is easier to measure than power, You could have a power gauge, but it would require that the gauge take RPM input in addition to torque.

2) Turboprops generally run at a single prop speed while in flight, so given constant RPM, torque is a fairly direct indication of power, and *POWER* is where it's at......................baby.

As far as torque making airplanes fly. Let's use the DC-6 as an example. The DC-6 has torquemeters, so it makes a convenient example. Our cruise setting for high gross weights uses a crankshaft speed of 2200 rpm. At medium gross weights we use a cruise power setting with 2000 RPM. Now here's the kicker; the *torque* at the lower power setting is actually higher than the torque at the higher power setting. Hmmmm, so, what happens if in cruise we go from the high power, lower torque setting to the lower power, higher torque setting? Does the airplane speed up or slow down? High torque should make it go faster, right? Torque is where it's at ............baby, and power is just a figment of some marketing department's imagination. Right? right? ok, then how do you explain that the airplane actually goes slower? Anyone? Beuller? (sound of crickets chirping) I can hear the wheels grinding ... "OK more torque, but less speed, hmmmmm....how do you explain that?"

Maybe there is something to power after all. . Ya think?

 

[I.P. Freley]

It's all about RPM, baby!

Just thought I'd stir the pot.

 

[A Squared]

It's all about RPM, baby!

Just thought I'd stir the pot.

Hehe, good stir. Tounge in cheek or no, you still make a good point: revering RPM and ignoring power is silly, but no sillier than saying power doesn't matter, only torque. If RPM were all it took to make a car go fast, Corvettes would all be powered by a Dremel moto-tool, turning at 20,000 RPM (I suppose the extension cord would limit your range)

 

[BD King]

This post is enough to torque you off.