Please help! Whats crankshaft Horsepower?
supadupasupraman
08-23-2003, 05:09 PM
:confused: where is horspower measured? I am always hearing crankshaft or wheel hospower. What is it?
ccc880
08-23-2003, 08:09 PM
When you see a hp rating, it is usually hp at the crankshaft (hp before it has to spin the tranny, driveshafts, axles, and wheels). The real hp (or hp at the wheels) is usually around 20hp less than the hp at the crankshaft because it (hp at the wheels) is the total power left after it has moved the drivetrain. Hope this helps (because I am bad at explaining things)!!
jeffescortlx
08-23-2003, 10:23 PM
Most car manufactuers rate there vehicals in crank hp, but when you get a dyno reading it's wheel hp.
V-8Fan
08-23-2003, 11:32 PM
Since I rarely read car magazines anymore, I dunno what they are saying these days, but they used to (maybe still do?) quote what they called "bhp", which means brake horsepower---and that means horsepower delivered to the wheels. I remember being very shocked at some of the brake horsepower figures I saw published...don't recall exactly, but they seemed at the time to be up to around 100 or more horsepower less than what an engine put out at the crankshaft. This was back in the 60s...maybe drivetrains are just more efficient these days. Or maybe my feeble memory just doesn't recall. :rolleyes:
supadupasupraman
08-24-2003, 12:22 AM
:p Thanks! That info is awsome. This may sound stupid, but i'm only 13 ok. Whats torque? :confused:
Fliquer
08-24-2003, 09:25 AM
Torque is twisting power. Horsepower is simply a function of torque
jeffescortlx
08-25-2003, 01:21 PM
Since I rarely read car magazines anymore, I dunno what they are saying these days, but they used to (maybe still do?) quote what they called "bhp", which means brake horsepower---and that means horsepower delivered to the wheels. I remember being very shocked at some of the brake horsepower figures I saw published...don't recall exactly, but they seemed at the time to be up to around 100 or more horsepower less than what an engine put out at the crankshaft. This was back in the 60s...maybe drivetrains are just more efficient these days. Or maybe my feeble memory just doesn't recall. :rolleyes:
People in the UK call it bhp, in the US I see a lot of whp (wheel hp)
Usally a FWD 5 speed takes away about 12-15%, auto are as high as 20%.
People in the UK call it bhp, in the US I see a lot of whp (wheel hp)
Usally a FWD 5 speed takes away about 12-15%, auto are as high as 20%.
supadupasupraman
08-26-2003, 06:12 PM
C'mon somone, in detail, what the hell is torque? Or do none of you so called " car experts" know! :chair:
SaabJohan
08-28-2003, 08:55 AM
Bhp means braked horsepower and that means just like it sounds like, that the engine is braked in a dyno, the power is not just a guess or similar.
All car manufacturers measure the power on the crankshaft, the powerloss to the wheels is usually 10-20% depending on the transmission.
There are several standards how to measure the engine power, there is also something called net and gross power depending on what help equipment that was used like generator, AC compressor and so on.
When an engine is braked this can be done in two ways, static or dynamic. With a static measurement the engine is held at a constant rpm for a time while a dynamic measurement is done by accelerating the engine through a given rpm range under a time. Car manufacturers usually use the static method and this is done under a long time since that will give the largest heatproblems and the lowest power.
All car manufacturers measure the power on the crankshaft, the powerloss to the wheels is usually 10-20% depending on the transmission.
There are several standards how to measure the engine power, there is also something called net and gross power depending on what help equipment that was used like generator, AC compressor and so on.
When an engine is braked this can be done in two ways, static or dynamic. With a static measurement the engine is held at a constant rpm for a time while a dynamic measurement is done by accelerating the engine through a given rpm range under a time. Car manufacturers usually use the static method and this is done under a long time since that will give the largest heatproblems and the lowest power.
pimpmaro
09-01-2003, 08:21 PM
C'mon somone, in detail, what the hell is torque? Or do none of you so called " car experts" know! :chair:
Wow... pushy for a 13 year old... :rolleyes: BTW, your question as already been answered. Torque is the twisting power of an engine or anything that turns. When measured in Ft-lbs, it is measured as the force (in the direction of rotation) produced at a point, that is 1 ft out from the center of rotation. Imagine a lever in a tangential position to the driveshaft that measures 1 ft long. Torque is the force put on the end of that lever.
BTW, horsepower is a made up number. Torque (ft-lbs) = (hp x 5252)/RPM. If you ever look at a dyno graph, torque and hp always cross at 5252 rpm. Basically this means that you can find one number from the other and that you cannot change the torque without changing the hp.
If you'd really like to get into a complex engine discussion, I can start next with BMEP, which is the Brake Mean Effective Pressure that an engine operates at, and which is the limiting factor of the power that an engine can reliably produce. :iceslolan
Wow... pushy for a 13 year old... :rolleyes: BTW, your question as already been answered. Torque is the twisting power of an engine or anything that turns. When measured in Ft-lbs, it is measured as the force (in the direction of rotation) produced at a point, that is 1 ft out from the center of rotation. Imagine a lever in a tangential position to the driveshaft that measures 1 ft long. Torque is the force put on the end of that lever.
BTW, horsepower is a made up number. Torque (ft-lbs) = (hp x 5252)/RPM. If you ever look at a dyno graph, torque and hp always cross at 5252 rpm. Basically this means that you can find one number from the other and that you cannot change the torque without changing the hp.
If you'd really like to get into a complex engine discussion, I can start next with BMEP, which is the Brake Mean Effective Pressure that an engine operates at, and which is the limiting factor of the power that an engine can reliably produce. :iceslolan
LancasterWannaBe
09-01-2003, 08:32 PM
Well shoot, I want to know about BMEP.
Tell me something about it if that isn't too vague.
Tell me something about it if that isn't too vague.
ivymike1031
09-01-2003, 10:02 PM
BTW, horsepower is a made up number. Torque (ft-lbs) = (hp x 5252)/RPM. If you ever look at a dyno graph, torque and hp always
cross at 5252 rpm....
Hmm, what if my axes are not in units of ft-lbf, rpm, and hp? Say, for example, they were in SI units, like N*m and kW, the way you're most likely to find them at an engine OEM? Then my dyno graph wouldn't follow your rule, would it? Heck, unless you're looking at a US hotrod magazine, chances are your dyno graph won't conform to the above...
If you'd really like to get into a complex engine discussion, I can start next with BMEP, which is the Brake Mean Effective Pressure that an engine operates at, and which is the limiting factor of the power that an engine can reliably produce.
BMEP? That's another made-up number! It's just the work per cycle divided by the fluid displaced per cycle! You can calculate it from displacement and torque, in much the same way that you can calculate power from torque & rpm... I wouldn't say that BMEP limits the power output of an engine, but it is a good indicator of how hard an engine is working.
cross at 5252 rpm....
Hmm, what if my axes are not in units of ft-lbf, rpm, and hp? Say, for example, they were in SI units, like N*m and kW, the way you're most likely to find them at an engine OEM? Then my dyno graph wouldn't follow your rule, would it? Heck, unless you're looking at a US hotrod magazine, chances are your dyno graph won't conform to the above...
If you'd really like to get into a complex engine discussion, I can start next with BMEP, which is the Brake Mean Effective Pressure that an engine operates at, and which is the limiting factor of the power that an engine can reliably produce.
BMEP? That's another made-up number! It's just the work per cycle divided by the fluid displaced per cycle! You can calculate it from displacement and torque, in much the same way that you can calculate power from torque & rpm... I wouldn't say that BMEP limits the power output of an engine, but it is a good indicator of how hard an engine is working.
supadupasupraman
09-03-2003, 10:03 PM
Heh, being pushy got me an anwer didn't it. :biggrin: You saw the numbers? 30 views and 4 replys. Crazy
( Thanks)
( Thanks)
pimpmaro
09-06-2003, 05:36 PM
Hmm, what if my axes are not in units of ft-lbf, rpm, and hp? Say, for example, they were in SI units, like N*m and kW, the way you're most likely to find them at an engine OEM? Then my dyno graph wouldn't follow your rule, would it? Heck, unless you're looking at a US hotrod magazine, chances are your dyno graph won't conform to the above...
Obviously there are conversion factors for those numbers to correct for using metric units. I haven't ever tried N*m and kW in that formula, but I'll tell you what. I'll take a dyno graph I have here and do the calculations later on and get back to this thread to see how accurate it is and whether or not they still cross at 5252.
BMEP? That's another made-up number! It's just the work per cycle divided by the fluid displaced per cycle! You can calculate it from displacement and torque, in much the same way that you can calculate power from torque & rpm... I wouldn't say that BMEP limits the power output of an engine, but it is a good indicator of how hard an engine is working.
Exactly right, I wasn't meaning to say that it is a limitation on the power of the engine, but you are right in that it does indicate how hard an engine is working. What I was trying to say was that using the BMEP, you can determine how hard an engine is working, and figure out how hard an engine can reliably work (for lack of a more eloquent way to put it). The rule I've heard is that an engine in stock form can be modified to handle up to 300 BMEP reliably (simply power adders, not strength components), while in fully stock form, it may be at 170 BMEP. This way you can calculate your maximum torque and then your maximum horsepower off of that giving you an idea of how reliable your engine will be at that power level. I'm personally not fully sold on the idea, but I find it very interesting and I am looking into it further here and there to see exactly how reliable these numbers are and how meaningful they are.
Obviously there are conversion factors for those numbers to correct for using metric units. I haven't ever tried N*m and kW in that formula, but I'll tell you what. I'll take a dyno graph I have here and do the calculations later on and get back to this thread to see how accurate it is and whether or not they still cross at 5252.
BMEP? That's another made-up number! It's just the work per cycle divided by the fluid displaced per cycle! You can calculate it from displacement and torque, in much the same way that you can calculate power from torque & rpm... I wouldn't say that BMEP limits the power output of an engine, but it is a good indicator of how hard an engine is working.
Exactly right, I wasn't meaning to say that it is a limitation on the power of the engine, but you are right in that it does indicate how hard an engine is working. What I was trying to say was that using the BMEP, you can determine how hard an engine is working, and figure out how hard an engine can reliably work (for lack of a more eloquent way to put it). The rule I've heard is that an engine in stock form can be modified to handle up to 300 BMEP reliably (simply power adders, not strength components), while in fully stock form, it may be at 170 BMEP. This way you can calculate your maximum torque and then your maximum horsepower off of that giving you an idea of how reliable your engine will be at that power level. I'm personally not fully sold on the idea, but I find it very interesting and I am looking into it further here and there to see exactly how reliable these numbers are and how meaningful they are.
ivymike1031
09-07-2003, 01:26 PM
an engine in stock form can be modified to handle up to 300 BMEP reliably
I assume that when you say "300 BMEP" you mean 300psi BMEP. 30bar BMEP (441psi) is a very hard number to reach, but a modified diesel can get pretty close. Many stock diesels run in the neighborhood of 20-24bar (294 to 353 psi) BMEP.
14bar (205psi) BMEP is a pretty decent rating for a naturally-aspirated gasoline engine.
there are conversion factors for those numbers to correct for using metric units...I'll take a dyno graph I have here and do the calculations later on and get back to this thread to see how accurate it is and whether or not they still cross at 5252.
Don't bother. 1/5252 is just a conversion factor to convert units from ft*lbf*rpm to HP. It doesn't matter what units you put on a dyno graph, or where the lines cross each other, as long as the units are shown on the plot. Heck, even if your graph was in ft*lbf and HP vs RPM, your lines wouldn't necessarily cross at 5252. The only time they would is if both of your y-axes had the same scalar values (as is commonly done). If it was useful, you could use different values on your torque axis than on your power axis, to exaggerate the scale of one versus the other (maybe to highlight a dip in the torque curve), and then the place where your lines cross would be arbitrary, depending on what range of numbers you picked on each axis.
I assume that when you say "300 BMEP" you mean 300psi BMEP. 30bar BMEP (441psi) is a very hard number to reach, but a modified diesel can get pretty close. Many stock diesels run in the neighborhood of 20-24bar (294 to 353 psi) BMEP.
14bar (205psi) BMEP is a pretty decent rating for a naturally-aspirated gasoline engine.
there are conversion factors for those numbers to correct for using metric units...I'll take a dyno graph I have here and do the calculations later on and get back to this thread to see how accurate it is and whether or not they still cross at 5252.
Don't bother. 1/5252 is just a conversion factor to convert units from ft*lbf*rpm to HP. It doesn't matter what units you put on a dyno graph, or where the lines cross each other, as long as the units are shown on the plot. Heck, even if your graph was in ft*lbf and HP vs RPM, your lines wouldn't necessarily cross at 5252. The only time they would is if both of your y-axes had the same scalar values (as is commonly done). If it was useful, you could use different values on your torque axis than on your power axis, to exaggerate the scale of one versus the other (maybe to highlight a dip in the torque curve), and then the place where your lines cross would be arbitrary, depending on what range of numbers you picked on each axis.
pimpmaro
09-07-2003, 07:06 PM
All I was meaning by saying that the graphs cross at 5252 is that when measuring torque in Ft-lbs and power in hp, the values are equal at 5252 rpm. I would try to discuss this further, but I've been studying all day and my mind is too far gone to provide a good arguement. But then again, this is about learning and not arguing isn't it. :wink:
pimpmaro
09-07-2003, 07:08 PM
Oh, and yes I was referring to psi. My mind doesn't work in bar very well and I've gotten into the bad habit of not specifying units when dealing with pressures. Sorry!
454Casull
09-12-2003, 06:09 PM
Most car manufactuers rate there vehicals in crank hp, but when you get a dyno reading it's wheel hp.
There are dynos that measure torque at the crank.
There are dynos that measure torque at the crank.
454Casull
09-12-2003, 06:11 PM
When you see a hp rating, it is usually hp at the crankshaft (hp before it has to spin the tranny, driveshafts, axles, and wheels). The real hp (or hp at the wheels) is usually around 20hp less than the hp at the crankshaft because it (hp at the wheels) is the total power left after it has moved the drivetrain. Hope this helps (because I am bad at explaining things)!!
Not necessarily. The Subaru WRX has what, 221HP? Only ~160hp gets to the wheels.
Also, the HP at a crankshaft, and the HP at end of a rigid shaft connected to the crankshaft is the same. Just picking on your wording. :) It's the inefficiency of the transmission that deletes some HP.
Not necessarily. The Subaru WRX has what, 221HP? Only ~160hp gets to the wheels.
Also, the HP at a crankshaft, and the HP at end of a rigid shaft connected to the crankshaft is the same. Just picking on your wording. :) It's the inefficiency of the transmission that deletes some HP.
454Casull
09-12-2003, 06:15 PM
One last thing (my apologies for the multiple posts) - SAE net HP, DIN HP and BHP are all the same thing, which is the engine dynoed on the flywheel with all accessories running. DIN HP, however, is roughly 1.01 (?) times greater than SAE net.
pimpmaro
09-16-2003, 03:01 AM
ACTUALLY... the differences between crank and wheel horsepower is more like a percentage of power. For example on my car, being a manual the drivetrain takes up about 12-15% of the power. From what I hear, an auto may take up 20% or more.
ales
09-16-2003, 07:51 AM
ACTUALLY... the differences between crank and wheel horsepower is more like a percentage of power. For example on my car, being a manual the drivetrain takes up about 12-15% of the power. From what I hear, an auto may take up 20% or more.
Actually, it has nothing to do with percentage. Ecample: a 100 chp car loses 15 hp (15%) through transmission and only 85 are delivered to the wheels. No, imagine you slap a big turbo on that engine and it now makes 200 chp, but leave the transmission unaltered. There is no reason for transmission losses to go up, so the car will lose the same 15 hp and will deliver 185 hp to the wheels. In the latter case the loss will be 7.5%.
So, in short, transmission losses are car-specific, and have nothing to do with the percentage of the engine power.
Actually, it has nothing to do with percentage. Ecample: a 100 chp car loses 15 hp (15%) through transmission and only 85 are delivered to the wheels. No, imagine you slap a big turbo on that engine and it now makes 200 chp, but leave the transmission unaltered. There is no reason for transmission losses to go up, so the car will lose the same 15 hp and will deliver 185 hp to the wheels. In the latter case the loss will be 7.5%.
So, in short, transmission losses are car-specific, and have nothing to do with the percentage of the engine power.
SaabJohan
09-16-2003, 11:22 AM
Actually, it has nothing to do with percentage. Ecample: a 100 chp car loses 15 hp (15%) through transmission and only 85 are delivered to the wheels. No, imagine you slap a big turbo on that engine and it now makes 200 chp, but leave the transmission unaltered. There is no reason for transmission losses to go up, so the car will lose the same 15 hp and will deliver 185 hp to the wheels. In the latter case the loss will be 7.5%.
So, in short, transmission losses are car-specific, and have nothing to do with the percentage of the engine power.
Actually it has to to with percentage. If we have 100 hp and 15 hp loss the loss with 200 hp will be approx. 30 hp. This is because of the friction in the gearbox, double the load (torque) or speed and we have doubled the friction. This isn't really that strange, and it can easily be confirmed with a measurement, just take the temperature of the oil at low power and high and you will notice the temperature will increase when power does (friction -> heat). This is also the reason most racingcars use a oilcooler for the transmission, not because they have transmissions with low efficiency.
The efficiency is usually between a little under 10% up to around 30%, best are FWD cars with manual gearboxes, worst are 4WD cars with automatics. In the case with the Subaru WRX the transmission loss is 27.6%, and this can be noticed on its fuelconsumption.
So, in short, transmission losses are car-specific, and have nothing to do with the percentage of the engine power.
Actually it has to to with percentage. If we have 100 hp and 15 hp loss the loss with 200 hp will be approx. 30 hp. This is because of the friction in the gearbox, double the load (torque) or speed and we have doubled the friction. This isn't really that strange, and it can easily be confirmed with a measurement, just take the temperature of the oil at low power and high and you will notice the temperature will increase when power does (friction -> heat). This is also the reason most racingcars use a oilcooler for the transmission, not because they have transmissions with low efficiency.
The efficiency is usually between a little under 10% up to around 30%, best are FWD cars with manual gearboxes, worst are 4WD cars with automatics. In the case with the Subaru WRX the transmission loss is 27.6%, and this can be noticed on its fuelconsumption.
ales
09-16-2003, 01:22 PM
And I'm proven wrong :p Live and learn.
So in a hypothetical situation of the 100 chp engine being substituted with a 1000 chp one, and providing the original transmission is able to take it, will the transmission loss be 150 hp? I understand your logic, but surely the formula can't be that linear?
So in a hypothetical situation of the 100 chp engine being substituted with a 1000 chp one, and providing the original transmission is able to take it, will the transmission loss be 150 hp? I understand your logic, but surely the formula can't be that linear?
ivymike1031
09-16-2003, 02:07 PM
And I'm proven wrong :p Live and learn.
So in a hypothetical situation of the 100 chp engine being substituted with a 1000 chp one, and providing the original transmission is able to take it, will the transmission loss be 150 hp? I understand your logic, but surely the formula can't be that linear?
to transmit the higher power, you'd need to increase rotational speed (and increase hydrodynamic losses), or you'd need to increase torque (and increase gear face loading + resulting friction), or some combination of the two... Then again, transmission efficiency at idle is quite a bit lower than it is at full load, so there is noticable non-linearity at the low end of the load scale. (idle is perhaps an over-simplified case, but low-load medium speed operation is usually less efficient than high-load medium speed operation for a given gearbox)
So in a hypothetical situation of the 100 chp engine being substituted with a 1000 chp one, and providing the original transmission is able to take it, will the transmission loss be 150 hp? I understand your logic, but surely the formula can't be that linear?
to transmit the higher power, you'd need to increase rotational speed (and increase hydrodynamic losses), or you'd need to increase torque (and increase gear face loading + resulting friction), or some combination of the two... Then again, transmission efficiency at idle is quite a bit lower than it is at full load, so there is noticable non-linearity at the low end of the load scale. (idle is perhaps an over-simplified case, but low-load medium speed operation is usually less efficient than high-load medium speed operation for a given gearbox)
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