Horsepower, torque, and engine design
05-21-2008, 07:41 PM
#26
Registered
Thread Starter
I thought I'd expand this to show how this actually affects getting power to the ground. Some people like to concentrate on torque saying it's what moves you even though it isn't. These people like to point out that a transmission is a torque multiplier and not a horsepower multiplier. This is true. Since it's true they use the logic that it is therefore torque that gets to the ground to do the work. Not so! Let's prove it!
First lets just get the standard hp/torque formulas out of the way.
HP x 5252 / RPM = Torque
TQ / 5252 x rpm = HP
What a transmission is really doing is getting POWER to the ground through torque multiplication. How so?
Let's once again throw out some numbers. I want to keep this easy so let's say the gear we are in is a 1:1 gear ratio. That way we don't complicate things with a further calculation even though the results would be the same. Now let's plug in a rear end gear ratio. Let's use the 4.44:1 that we have all come to know. Now we need to know two other things, hp and rpm. Let's say that we have the engine revving up pretty high at 8000 rpm. I understand that in this gear it would be pretty darn fast but let's just remember this is example and not a real world speed trial. Now let's also say that we are producing 200 hp at this rpm. Again don't bust my ***** on real world comparisons to the RX-8. It's an example. This is all the info we need.
The first thing we need to do is to figure out how much torque the engine is producing at this rpm. Plug the numbers into the formula.
200HP x 5252 / 8000 rpm = 131.3 ft lbs. of torque.
Now some people would say that it is through torque multiplication that makes it possible for the vehicle to move so let's again plug the torque into the known gear ratio that we are using. Remember we have a 1:1 gear chosen with a 4.44:1 rear end.
131.3 ft lbs of torque stays 131.3 through a 1:1 gear. That means we now just need to figure out how the rear end changes it. Since gears are torque multipliers, we take 131.3 ft lbs x 4.44 to get 582.972 ft lbs of torque. That's alot of torque to the ground and the reason why some people say it's torque that moves you. However it's not. It's horsepower. Remember horsepower is in fact torque over time but since time is involved, speed also needs to be known. Fortunately we know it. I would argue that since the engine is producing 200 hp, that the torque multiplication hasn't changed that and that we are still getting 200 to the ground. We are. Here's how to prove it.
In order to increase torque through a gear ratio, we need to do one other thing and that is to slow down speed. In our case we have an engine that is revving at 8000 rpm but with the 1:1 gear chosen which changes nothing and the 4.44:1 rear end, we have slowed down this rotational speed at the wheels. We take 8000 / 4.44 = 1801.8. That is our wheel rpm. It's not over. We need to prove it's power that moves us. Let's plug in numbers yet again.
We now use 1801.8 as our rpm. We use 582.972 as our known torque. We need to figure out the horsepower at the ground based on this. Easy.
582.972 / 5252 x 1801.8 = 200 HP!!! It is power to the ground and not torque that moves us!!! No I am not factoring in drivetrain loss. That's understood. This assumes a 100% efficient drivetrain and unfortunately that changes somewhat with the chosen gear.
My desire to use an all electric motor system is because they have max torque at zero rpm. They need to!!! They have a flat horsepower curve. The torque curve falls on them as rpm rises. If I had a 100 hp generator sending a constant power supply capable of 100 hp to the electric motor at all times, the car would have this to the ground no matter what the rpm of the wheels are (except 0). Can you imagine having 100 hp off idle to the ground! We could use smaller peak power engines since it's average power that counts. Smaller is lighter, and more efficient.
To go back to the original topic a bit, a smaller generator engine that makes it's peak power up at higher rpms would be better than a larger engine that makes peak power lower in the rpm range. The engine wouldn't have the total torque and could be built much lighter.
Torque doesn't matter when it comes to moving you. It does matter when it comes to engine strength though.
First lets just get the standard hp/torque formulas out of the way.
HP x 5252 / RPM = Torque
TQ / 5252 x rpm = HP
What a transmission is really doing is getting POWER to the ground through torque multiplication. How so?
Let's once again throw out some numbers. I want to keep this easy so let's say the gear we are in is a 1:1 gear ratio. That way we don't complicate things with a further calculation even though the results would be the same. Now let's plug in a rear end gear ratio. Let's use the 4.44:1 that we have all come to know. Now we need to know two other things, hp and rpm. Let's say that we have the engine revving up pretty high at 8000 rpm. I understand that in this gear it would be pretty darn fast but let's just remember this is example and not a real world speed trial. Now let's also say that we are producing 200 hp at this rpm. Again don't bust my ***** on real world comparisons to the RX-8. It's an example. This is all the info we need.
The first thing we need to do is to figure out how much torque the engine is producing at this rpm. Plug the numbers into the formula.
200HP x 5252 / 8000 rpm = 131.3 ft lbs. of torque.
Now some people would say that it is through torque multiplication that makes it possible for the vehicle to move so let's again plug the torque into the known gear ratio that we are using. Remember we have a 1:1 gear chosen with a 4.44:1 rear end.
131.3 ft lbs of torque stays 131.3 through a 1:1 gear. That means we now just need to figure out how the rear end changes it. Since gears are torque multipliers, we take 131.3 ft lbs x 4.44 to get 582.972 ft lbs of torque. That's alot of torque to the ground and the reason why some people say it's torque that moves you. However it's not. It's horsepower. Remember horsepower is in fact torque over time but since time is involved, speed also needs to be known. Fortunately we know it. I would argue that since the engine is producing 200 hp, that the torque multiplication hasn't changed that and that we are still getting 200 to the ground. We are. Here's how to prove it.
In order to increase torque through a gear ratio, we need to do one other thing and that is to slow down speed. In our case we have an engine that is revving at 8000 rpm but with the 1:1 gear chosen which changes nothing and the 4.44:1 rear end, we have slowed down this rotational speed at the wheels. We take 8000 / 4.44 = 1801.8. That is our wheel rpm. It's not over. We need to prove it's power that moves us. Let's plug in numbers yet again.
We now use 1801.8 as our rpm. We use 582.972 as our known torque. We need to figure out the horsepower at the ground based on this. Easy.
582.972 / 5252 x 1801.8 = 200 HP!!! It is power to the ground and not torque that moves us!!! No I am not factoring in drivetrain loss. That's understood. This assumes a 100% efficient drivetrain and unfortunately that changes somewhat with the chosen gear.
My desire to use an all electric motor system is because they have max torque at zero rpm. They need to!!! They have a flat horsepower curve. The torque curve falls on them as rpm rises. If I had a 100 hp generator sending a constant power supply capable of 100 hp to the electric motor at all times, the car would have this to the ground no matter what the rpm of the wheels are (except 0). Can you imagine having 100 hp off idle to the ground! We could use smaller peak power engines since it's average power that counts. Smaller is lighter, and more efficient.
To go back to the original topic a bit, a smaller generator engine that makes it's peak power up at higher rpms would be better than a larger engine that makes peak power lower in the rpm range. The engine wouldn't have the total torque and could be built much lighter.
Torque doesn't matter when it comes to moving you. It does matter when it comes to engine strength though.
05-22-2008, 02:16 PM
#27
Administrator
i would actually put money on a Software issue reporting error rather than any other cause for that day. I have seen it myself on several occasions. With Dynojet dynometers they use spark timing to determine rpm . but most often the software doesnt have rotary timing in its software so you have to choose the most accurate out of the possibilities in the software. choose the wrong one and the HP comes out wrong.
05-27-2008, 08:00 PM
#28
TroublemakrExtraordinaire
Actually what they were most upset about is that an AT posted higher numbers than the MTs. The explenation given was that "Yoshiya-san didn't change the relative wheel speed to run time setting on the dyno when we put your car up." The thing I don't understand is why a dyno would want to use the engine's RPM to calculate RWHP since it can present perfectly reliable results by taking the measured torque and it knows the dyno wheel size and the load that it is presenting to the car. It also knows the acceleration rate.
And RG, thank you for expanding the topic. It is very usefull and interesting information. Could you help me understand the way a Dyno works?
And RG, thank you for expanding the topic. It is very usefull and interesting information. Could you help me understand the way a Dyno works?
05-27-2008, 08:44 PM
#29
So the horsepower performs the Work and the torque is the momentum?
very educational, thanks
(I am working on a language degree and business, so give me some slack too, jk)
very educational, thanks
(I am working on a language degree and business, so give me some slack too, jk)
Last edited by fahrfegneugen; 05-27-2008 at 11:04 PM.
05-29-2008, 09:16 PM
#30
Registered User
Horsepower is a somewhat arbitrary figure relating the rate at which torque is developed.
1 hp = 550 lb-ft/sec.
These quantities are related in basic physics where it's stated that power is energy per unit time, or the rate at which work is performed.
For example, if an object of 1 lb is raised to a height of 1 ft, 1lb-ft of energy has been transferred to it. If it was raised in 1 second, then 1/550 hp was produced in the process. More simply, if 550 lb were raised a height of 1 ft in 1 second, 1 hp was required to perform that.
Additionally, 1 HP = 746 Watts. Ever notice that the europeans rate their engines in KW, or kilowatts. 1 watt = 1 newton-meter/second. A newton is a MSI system measure of force and is equal to about 2.2/9.8 lbs.
The constant 5254 used to convert torque to HP at a specific RPM is derived very easily from
scalar = (550 x 60)/(2pi) and it has units of (revolution-seconds)/(min radians/revolution)...yielding just seconds in the end..the units cancel and radians are unitless. It essentially converts the RPM's to seconds and embeds the 550 scalar (from the 550 lbs-ft/sec).
I think I got that right, I'm tired.
1 hp = 550 lb-ft/sec.
These quantities are related in basic physics where it's stated that power is energy per unit time, or the rate at which work is performed.
For example, if an object of 1 lb is raised to a height of 1 ft, 1lb-ft of energy has been transferred to it. If it was raised in 1 second, then 1/550 hp was produced in the process. More simply, if 550 lb were raised a height of 1 ft in 1 second, 1 hp was required to perform that.
Additionally, 1 HP = 746 Watts. Ever notice that the europeans rate their engines in KW, or kilowatts. 1 watt = 1 newton-meter/second. A newton is a MSI system measure of force and is equal to about 2.2/9.8 lbs.
The constant 5254 used to convert torque to HP at a specific RPM is derived very easily from
scalar = (550 x 60)/(2pi) and it has units of (revolution-seconds)/(min radians/revolution)...yielding just seconds in the end..the units cancel and radians are unitless. It essentially converts the RPM's to seconds and embeds the 550 scalar (from the 550 lbs-ft/sec).
I think I got that right, I'm tired.
Last edited by digitalSniperX1; 05-29-2008 at 09:34 PM.
05-20-2020, 07:32 PM
#31
Registered
Working around diesel engines up to 2000 hp at work all day, I started to think about various engines, sizes, types, and their robustness. Diesel engines are typically very large and very heavy. They are also very tough. Even diesels that dont' make a whole lot of peak horsepower are over built compared to gasoline engines of the same power level. I never really thought about why but my first inclination was the same as everyone else I've ever asked.
When the topic of engine robustness pops up in relation to diesels, the first thing you hear is that they need to be overbuilt because they have higher compression ratios. Sounds logical. I've also heard that they are overbuilt because they are typically designed to last longer. That's fair. It's obviously not due to rpms as these just don't rev that high.
...........
FYI diesel engines works on totally difference principle, combustion in constant pressure whereas counterpart gasoline engine works on combustion in constant volume.
Serve you self a favour and read bout these key subjects : diesel cycle , otto cycle
Simply, diesel engines must knock to work BUT knock will destroyed gasoline engine, so they must be robust. that knock is from piston hitting cylinder wall like a sledge hammer, hence funky noise of diesels. As diesel piston move from TDC to BDC the pressure over crown of piston stay almost constant and its one of other limitation over
max rev and.... story goes on, they are two different space ships. Also back in oil company days I work with cummins, 2-strokes supercharged 4 valves, V16 to gas turbines. good old day.
05-20-2020, 09:08 PM
#33
Registered
I got them from 2 years technical school, 2,5 years auto mechanic college, 3 years offshore oil company and countless books, exam...
05-20-2020, 09:19 PM
#34
Ok .. I googled the constant volume/constant pressure thing . Curious as to why you felt the need to mention it and what it had to do with what rotary god had to say?
Btw knock noise is from combustion not piston slapping ...just googled that as well.
Btw knock noise is from combustion not piston slapping ...just googled that as well.
Last edited by Brettus; 05-20-2020 at 10:08 PM.
05-21-2020, 12:18 PM
#35
Smoking turbo yay
He is trying to build that Rolls Royce diesel rotary.
But yes, diesel engines runs on "knocking" as you are making the fuel combust merely from the high temperature from the extreme compression, which demands stronger engine construction.
But yes, diesel engines runs on "knocking" as you are making the fuel combust merely from the high temperature from the extreme compression, which demands stronger engine construction.
05-23-2020, 04:20 PM
#40
Registered
constant pressure = more torque, not essentially the connecting rods and other things mentioned.
05-23-2020, 04:29 PM
#41
Registered
diesels are knocking but they designed for it, mechanically, thermodynamically and...
05-23-2020, 04:45 PM
#42
Registered
What is wrong is wrong and the most toxic is wrong info. You know what, I am quite used to your behaviour for attacking what ever is against your personal
believe, you are kinda very guy who has one book in hand and seeking all answer of life on that book.
You better stop sneaking others post and force them your opinion, clearly you attache any user by saying "it has done 10 years go" "it is old new" and all sort of
things which is normal. Simply get life mate.
I fell free to correct any wrong info from any time on any place, since it could misguide others. And unlike many others I do not shove my opinion as theory,
I will give explanation, source, provide documents, unlike some doing monkey business and meme.
When people are short on explanation they give prescription.
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