Power and Torque

[1engineer]

I did not want to post this in another thread to get too far off topic but Okki made a good, interesting post about diesel vs. gas engines. Unfortunately, for every good post like Okkis there are many others on the topic of diesel vs. gas engines and their advantages that are not correct. Many of you seem to think that because a diesel engine inherently has more torque that this equates to more power. I have read these posts in the past and now is the time to post a few facts on this topic:

To understand these concepts you first must know a few definitions.

Torque:
TORQUE is defined as a FORCE around a given point, applied at a RADIUS from that point. Note that the unit of TORQUE is one pound-foot (often misstated), while the unit of WORK is one foot-pound.

Power:
POWER is the measure of how much WORK can be done in a specified TIME. Power can be measured in many different units but for our purposes we will deal with horsepower. The definition of one horsepower is 33,000 foot-pounds per minute.

Now for the math:
HP = Torque x RPM ÷ 5252

Let's look at this formula for a minute...
Horsepower = Torque times revolutions per minute divided by 5252. If you care where the constant 5252 comes from PM me.
Now, pushing a vehicle along a highway at 75 mph takes power, and you can see from the formula above what power is. You need torque and you need revolutions. A diesel engine can give you the same HP as a gasoline engine at a lower RPM. If you rearrange a few things a gasoline engine can give you the torque of a diesel engine by adding more power at the same RPM.

Now, what do you really want? Do you want more torque at a low RPM or do you want more HP at a low RPM? I know what you want - you want an engine that puts out 1000 lb-ft of torque and has 500 hp and gets 50 mpg. Sorry. Engines are designed to provide adequate performance in certain conditions. Today's conditions are all about efficiency while providing adequate performance. Some of you that make all-encompassing statements such as "If we had a diesel engine in the 4Runner I would buy one," or "If it still had a V8 I would be driving a 5th gen now" couldn't be more wrong and don't have a clue what you are talking about. What if they put a diesel engine in the 4Runner and geared it for gobs of low end power but could only go down the highway at 55 mph top speed? How about if they put a V8 in a 4Runner with 600 hp but only got 5 mpg? See what I mean? The 5th gen V6 was designed as a compromise around power, durability and efficiency and I think they did a good job.

Remember, there is nothing free in the engineering world. If you increase something then something else decreases. It's math. It could be speed, efficiency or longevity of components that suffer depending on the application. I hope this helps some of you to understand these relationships between torque and power.

 

[philsey]

I love this forum - in about an hour I go from phillyd's, um, humor, to 1E's enlightenment/edumacation.

 

[Jayhawk5G]

I think a lot of people are interested in a diesel in hopes that we could get similar numbers to the yet unreleased 2013/2014 Jeep Grand Cherokee CRD 237hp/406tq and 23 mpg city and 33 mpg highway. The high torque available at low rpm would help for off-roading, and would allow the vehicle to accelerate briskly and currently no gas engine is touching those MPG numbers with 4x4 and similar performance. I'm sure it would up the tow rating as well.

I think a lot of people mention the V8, and mean to say more low end torque. That is something I have missed coming from my Jeep Grand Cherokee, the 5.7 at all times had gobs of torque. Even slightly pressing the accelerator got the vehicle moving without hesitation. The 5th gen for various reasons requires you press the accelerator a little harder, though when you do it's far from sluggish or slow.

Personally I would love a little more torque. I wish for 2013 they would have added DI to the engine, I think 300/300 would be achievable with a small improvement in MPG's. I'm also interested in a gas V6 with twin or single turbo as multiple sources are reporting that Toyota is considering adding turbocharging across the board to meet power/mpg requirements.

 

[Antman]

Nice post 1E!

I wanna know where that 5252 comes from- wait- wasn't that a Vanhalen album? Oh- nevermind...

Still wanna know though.

 

[Blacksunshyne]

Now, what do you really want? Do you want more torque at a low RPM or do you want more HP at a low RPM? I know what you want - you want an engine that puts out 1000 lb-ft of torque and has 500 hp and gets 50 mpg. Sorry. Engines are designed to provide adequate performance in certain conditions. Today's conditions are all about efficiency while providing adequate performance. Some of you that make all-encompassing statements such as "If we had a diesel engine in the 4Runner I would buy one," or "If it still had a V8 I would be driving a 5th gen now" couldn't be more wrong and don't have a clue what you are talking about. What if they put a diesel engine in the 4Runner and geared it for gobs of low end power but could only go down the highway at 55 mph top speed? How about if they put a V8 in a 4Runner with 600 hp but only got 5 mpg? See what I mean? The 5th gen V6 was designed as a compromise around power, durability and efficiency and I think they did a good job.

Remember, there is nothing free in the engineering world. If you increase something then something else decreases. It's math. It could be speed, efficiency or longevity of components that suffer depending on the application. I hope this helps some of you to understand these relationships between torque and power.

What I highlighted in red is of concern. Let me say that the V6 is a good little motor for this truck. I do feel if it were offered with a 6 speed manual it woud quell about 80% of the underpower complaints. I do believe the problem there stems from the shift points Toyota uses on the auto transmission.

It is totally possible to put a 4cyl. turbo diesel in the 4runner and gear it so it runs at a comfortable cruising speed say 70+/-, with low RPMs, and it still have more available torque than Toyta's current gasoline engine. It would put out more torque, less horsepower and get compairable (or better) fuel milage than the current combination.

I have a 1972 deuce and a half with a diesel (multifuel) engine that will cruise at 55 MPH at around 2,000 RPM and that is 40+ year old technology. It is a 12,000 pound truck with worse aerodynamics than the 4runner and still gets about 10-12 MPG. So I think saying that Toyota (who uses diesels pretty much everywhere else in the world) (thanks EPA) could not put a diesel motor in the 4runner that is capable of being a better overall package than what is currently offered is not entirely true.

On to the V8, again saying that the 4runner would need a 600 HP gas motor seems a bit extreme. Toyota would be perfectly capable of putting a well manner V8 in the 5th Generation that would return MPG numbers that were pretty close to what the current V6 is putting out.

I understand you are trying to make a point here, but if we don't keep our discussion based in the real world then it is pretty much useless.

 

[KodeRush]

Not to steal 1E's thunder, just save someone's time:

1 HP = 33,000 foot-pounds per minute

5252 = 33000 / (2 x PI)

 

[1engineer]

Nice post 1E!

I wanna know where that 5252 comes from- wait- wasn't that a Vanhalen album? Oh- nevermind...

Still wanna know though.

The album was 5150 lol.

You REALLY want to know? Ok, you need to know a little history. I know the story but I pulled odds and ends from other sources:

First -
The development of the steam engine provided a reason to compare the output of horses with that of the engines that could replace them. In 1702, Thomas Savery wrote in The Miner's Friend "So that an engine which will raise as much water as two horses, working together at one time in such a work, can do, and for which there must be constantly kept ten or twelve horses for doing the same. Then I say, such an engine may be made large enough to do the work required in employing eight, ten, fifteen, or twenty horses to be constantly maintained and kept for doing such a work…" The idea was later used by James Watt to help market his improved steam engine. He had previously agreed to take royalties of one third of the savings in coal from the older Newcomen steam engines. This royalty scheme did not work with customers who did not have existing steam engines but used horses instead. Watt determined that a horse could turn a mill wheel 144 times in an hour (or 2.4 times a minute). The wheel was 12 feet in radius; therefore, the horse travelled 2.4 × 2π × 12 feet in one minute. Watt judged that the horse could pull with a force of 180 pounds.:
This was rounded to an even 33,000 ft·lbf/min. See the formula way below. NOW to get to the constant 5252:

TORQUE = FORCE x RADIUS.

If we divide both sides of that equation by RADIUS, we get:

(a) FORCE = TORQUE ÷ RADIUS

Now, if DISTANCE per revolution = RADIUS x 2 x π, then

(b) DISTANCE per minute = RADIUS x 2 x π x RPM

We already know

(c) POWER = FORCE x DISTANCE per minute

So if we plug the equivalent for FORCE from equation (a) and distance per minute from equation (b) into equation (c), we get:

POWER = (TORQUE ÷ RADIUS) x (RPM x RADIUS x 2 x π)

Dividing both sides by 33,000 to find HP,

HP = TORQUE ÷ RADIUS x RPM x RADIUS x 2 x π ÷ 33,000

By reducing, we get

HP = TORQUE x RPM x 6.28 ÷ 33,000

Since

33,000 ÷ 6.2832 = 5252

Therefore

HP = TORQUE x RPM ÷ 5252

Note that at 5252 RPM, torque and HP are equal. At any RPM below 5252, the value of torque is greater than the value of HP; Above 5252 RPM, the value of torque is less than the value of HP.

 

[crunchcity]

This particular compromise probably wasn't for the primary benefit of the consumer but other reasons within the larger scope of their overall business operations imo.

 

[1engineer]

What I highlighted in red is of concern. Let me say that the V6 is a good little motor for this truck. I do feel if it were offered with a 6 speed manual it woud quell about 80% of the underpower complaints. I do believe the problem there stems from the shift points Toyota uses on the auto transmission.

It is totally possible to put a 4cyl. turbo diesel in the 4runner and gear it so it runs at a comfortable cruising speed say 70+/-, with low RPMs, and it still have more available torque than Toyta's current gasoline engine. It would put out more torque, less horsepower and get compairable (or better) fuel milage than the current combination.

I have a 1972 deuce and a half with a diesel (multifuel) engine that will cruise at 55 MPH at around 2,000 RPM and that is 40+ year old technology. It is a 12,000 pound truck with worse aerodynamics than the 4runner and still gets about 10-12 MPG. So I think saying that Toyota (who uses diesels pretty much everywhere else in the world) (thanks EPA) could not put a diesel motor in the 4runner that is capable of being a better overall package than what is currently offered is not entirely true.

On to the V8, again saying that the 4runner would need a 600 HP gas motor seems a bit extreme. Toyota would be perfectly capable of putting a well manner V8 in the 5th Generation that would return MPG numbers that were pretty close to what the current V6 is putting out.

I understand you are trying to make a point here, but if we don't keep our discussion based in the real world then it is pretty much useless.

Totally understand. I used "extreme" examples exactly to make a point. You mentioned above putting a 4 cylinder diesel in a 4Runner. Maybe some day and using the old V8 from the 4th gen would be fine too. I would say with some level of experience that Toyota has plans for this V6 that could not be applied to the older V6 or V8. Remember when things are designed they are designed well ahead of their use and direct injection, turbo or something else could already be planned. The last point is simply economics and demand. Right now they think they can make more money using the V6 than developing Tier IV components for their diesel to be used over here. That, and very few want them apparently (people from this forum excluded lol).

Not to steal 1E's thunder, just save someone's time:

1 HP = 33,000 foot-pounds per minute

5252 = 33000 / (2 x PI)

Yeah but then someone would ask where the 33,000 came from!

 

[Koz]

I would be driving a 5th gen 4Runner if the 4.6 V8 was available! The 4Runner did not have enough towing capacity (and no rear air springs). Also, I believe if the 5th gen 4Runner had the 4.6 V8 w/6 speed trans it would get as good mileage (or better) as the V6 4Runner. The reason I say this is because I have a GX460 and have gotten 22 mpg under ideal conditions and the GX is 500 lbs. heavier. There is a HUGE difference between the 4.6 V8 and the 4.0 V6!

Koz

 

[UFG8R Runner]

Where do I sign?

Dear 1engineer,

In reference to your statement:
"How about if they put a V8 in a 4Runner with 600 hp but only got 5 mpg?"

Where can I find this rumored beast? It sounds AWESOME!

 

[Koz]

There is a reason why Toyota did not put direct injection in 5th gen 4Runner and will not use it anytime in the near future. It has not been perfected and is causing major problems in just about all engines that use it (including Toyota/Lexus). They have to find a way to keep carbon from building up in the engine.

Koz

 

[Curt Sauve]

It's all about balance, interesting read in the link

Speed Costs Money

 

[Stuck CAPS]

The album was 5150 lol.

You REALLY want to know? Ok, you need to know a little history. I know the story but I pulled odds and ends from other sources:

First -
The development of the steam engine provided a reason to compare the output of horses with that of the engines that could replace them. In 1702, Thomas Savery wrote in The Miner's Friend "So that an engine which will raise as much water as two horses, working together at one time in such a work, can do, and for which there must be constantly kept ten or twelve horses for doing the same. Then I say, such an engine may be made large enough to do the work required in employing eight, ten, fifteen, or twenty horses to be constantly maintained and kept for doing such a work…" The idea was later used by James Watt to help market his improved steam engine. He had previously agreed to take royalties of one third of the savings in coal from the older Newcomen steam engines. This royalty scheme did not work with customers who did not have existing steam engines but used horses instead. Watt determined that a horse could turn a mill wheel 144 times in an hour (or 2.4 times a minute). The wheel was 12 feet in radius; therefore, the horse travelled 2.4 × 2π × 12 feet in one minute. Watt judged that the horse could pull with a force of 180 pounds.:
This was rounded to an even 33,000 ft·lbf/min. See the formula way below. NOW to get to the constant 5252:

TORQUE = FORCE x RADIUS.

If we divide both sides of that equation by RADIUS, we get:

(a) FORCE = TORQUE ÷ RADIUS

Now, if DISTANCE per revolution = RADIUS x 2 x π, then

(b) DISTANCE per minute = RADIUS x 2 x π x RPM

We already know

(c) POWER = FORCE x DISTANCE per minute

So if we plug the equivalent for FORCE from equation (a) and distance per minute from equation (b) into equation (c), we get:

POWER = (TORQUE ÷ RADIUS) x (RPM x RADIUS x 2 x π)

Dividing both sides by 33,000 to find HP,

HP = TORQUE ÷ RADIUS x RPM x RADIUS x 2 x π ÷ 33,000

By reducing, we get

HP = TORQUE x RPM x 6.28 ÷ 33,000

Since

33,000 ÷ 6.2832 = 5252

Therefore

HP = TORQUE x RPM ÷ 5252

Note that at 5252 RPM, torque and HP are equal. At any RPM below 5252, the value of torque is greater than the value of HP; Above 5252 RPM, the value of torque is less than the value of HP.

Your physics education makes me tear up. :')

 

[westwind77]

My head hurts now, thanks.

Right pedal = go

Left pedal = stop

 

[Antman]

Thanks! Now I'll just read that 50 or 60 times before it sinks in...


BTW- I know it's 5150- I can definitely hang with anyone when it comes to Rock N Roll!:guitar3:

 

[1engineer]

Thanks! Now I'll just read that 50 or 60 times before it sinks in...


BTW- I know it's 5150- I can definitely hang with anyone when it comes to Rock N Roll!:guitar3:

Don't you remember that time I told you that at 5252 rpm, torque and hp are equal? Well, now you know why!

 

[Okki]

My head hurts now, thanks.

Right pedal = go

Left pedal = stop

Okki :frisky:

 

[Ryan1975]

After reading this thread...I've made up my mind.














I'm pulling the 6.2L from the Yukon XL Denali and putting in a Duramax.

The 6.2L is going in the 4Runner.