Prospective 981 GT4 Owners Discussion Forum.
Discussion
J-P said:
What is BHP then, as it's this figure that I've always seen as something slightly different to HP or PS (which are pretty much always quoted as identically equal).
Technically, its gross engine horsepower (i.e. the SAE standard used before circa 1970). HP is the net engine horsepower standard that replaced it. PS is also a net engine horsepower standard but controlled by DIN rather than SAE as previously mentioned. These net power figures are at the crankshaft of the engine as per the relevant standards. The numbers are J1349 and DIN 70020 if you want to look them up.As also mentioned, SAE uses imperial measurements to calculate the work portion of the power figure while DIN uses metric measurements to calculate the work portion of the final power figure.
The whole use of terms in relation to cars in a mess though with people using and misusing them quite freely.
While kW is the required format here in the EU at least marketing blurb sticks with PS or HP though as its what people respond to. I suspect that if power in kW was larger than the equivalent power in PS or HP this wouldn't be the case.
I know I should - sometimes, I just can't help myself!
fioran0 said:
J-P said:
What is BHP then, as it's this figure that I've always seen as something slightly different to HP or PS (which are pretty much always quoted as identically equal).
Technically, its gross engine horsepower (i.e. the SAE standard used before circa 1970). HP is the net engine horsepower standard that replaced it. PS is also a net engine horsepower standard but controlled by DIN rather than SAE as previously mentioned. These net power figures are at the crankshaft of the engine as per the relevant standards. The numbers are J1349 and DIN 70020 if you want to look them up.As also mentioned, SAE uses imperial measurements to calculate the work portion of the power figure while DIN uses metric measurements to calculate the work portion of the final power figure.
The whole use of terms in relation to cars in a mess though with people using and misusing them quite freely.
While kW is the required format here in the EU at least marketing blurb sticks with PS or HP though as its what people respond to. I suspect that if power in kW was larger than the equivalent power in PS or HP this wouldn't be the case.
J-P said:
Thanks, Neil. Very helpful. So DIN HP and PS are identically equivalent. BHP is very different but actually currently misused to differentiate SAE HP from DIN HP. Is that right? Also do you know what the conversion rate for true BHP to PS would be? Cheers J-P
J-P said:
PS = 0.986BHP
This??Guys
You do know that all of these figures are just theoretical calculations? The real measurement is torque in Ibs/ft. These other measures just use the torque figure and use the RPM where the peak torque is made to come up with a HP, BHP or PS figure.
Im not saying it has no relevance, it does, but you are getting way to hung up on it.
You do know that all of these figures are just theoretical calculations? The real measurement is torque in Ibs/ft. These other measures just use the torque figure and use the RPM where the peak torque is made to come up with a HP, BHP or PS figure.
Im not saying it has no relevance, it does, but you are getting way to hung up on it.
sidicks said:
J-P said:
Thanks, Neil. Very helpful. So DIN HP and PS are identically equivalent. BHP is very different but actually currently misused to differentiate SAE HP from DIN HP. Is that right? Also do you know what the conversion rate for true BHP to PS would be? Cheers J-P
J-P said:
PS = 0.986BHP
This??mollytherocker said:
Guys
You do know that all of these figures are just theoretical calculations? The real measurement is torque in Ibs/ft. These other measures just use the torque figure and use the RPM where the peak torque is made to come up with a HP, BHP or PS figure.
Im not saying it has no relevance, it does, but you are getting way to hung up on it.
oh man!You do know that all of these figures are just theoretical calculations? The real measurement is torque in Ibs/ft. These other measures just use the torque figure and use the RPM where the peak torque is made to come up with a HP, BHP or PS figure.
Im not saying it has no relevance, it does, but you are getting way to hung up on it.
You are confusing all sorts of different units and what they mean in that post. I don't want to appear dismissive, I would dearly like to try and reply in a way that you might enjoy but theres no way its going to happen, especially on a forum. Its beyond its abilities as a delivery service and beyond my available time.
If you want me to recommend some books to you, drop me a message and I will have a look over some books or what colleagues would suggest to provide an introduction.
fioran0 said:
mollytherocker said:
Guys
You do know that all of these figures are just theoretical calculations? The real measurement is torque in Ibs/ft. These other measures just use the torque figure and use the RPM where the peak torque is made to come up with a HP, BHP or PS figure.
Im not saying it has no relevance, it does, but you are getting way to hung up on it.
oh man!You do know that all of these figures are just theoretical calculations? The real measurement is torque in Ibs/ft. These other measures just use the torque figure and use the RPM where the peak torque is made to come up with a HP, BHP or PS figure.
Im not saying it has no relevance, it does, but you are getting way to hung up on it.
You are confusing all sorts of different units and what they mean in that post. I don't want to appear dismissive, I would dearly like to try and reply in a way that you might enjoy but theres no way its going to happen, especially on a forum. Its beyond its abilities as a delivery service and beyond my available time.
If you want me to recommend some books to you, drop me a message and I will have a look over some books or what colleagues would suggest to provide an introduction.
Everything else is a calculation based on the torque measurement?
mollytherocker said:
You do know that all of these figures are just theoretical calculations? The real measurement is torque in Ibs/ft. These other measures just use the torque figure and use the RPM where the peak torque is made to come up with a HP, BHP or PS figure.
The only true measure taken from an engine is the torque?
Everything else is a calculation based on the torque measurement?
What is Power and what is its relationship with energy and work (or in specific reference to your question, torque)?The only true measure taken from an engine is the torque?
Everything else is a calculation based on the torque measurement?
fioran0 said:
J-P said:
BHP as used by most manufacturers is actually SAE HP which isn't the same as BHP which is a gross power figure.
I suspect you won't find any car manufacturers using BHP. In fact you shouldn't find anyone using BHP in their literature at all unless they are referring to an old car. I'd like to avoid disappearing down the rabbit hole on this completely if I can on this, its now so far off topic it needs a new sat nav disc.
This explanation isn't meant to be exhaustive, its just an attempt to try and summarise things.
BHP is the unit used to express Power on engines tested to SAE standards prior to circa 1970. It used imperial units ( the exact same as the later SAE HP test does) but the test itself measured gross engine output. 1 BHP was/is equal to 550 foot pounds per second.
HP was introduced along with a new SAE standard to replace the old standard detailed above. The use of HP was to prevent confusion between the figure obtained from this standard and that obtained from the old standard which gave a result in BHP.
It still used imperial units, in fact 1 HP is also equal to 550 foot pounds per second however the test now provided a Power figure for net engine output. This is the crucial difference. A BHP value and an HP value are therefore not comparable, not because the units differ (1 BHP and 1 HP both equal 550ftlbs/s) but because the values obtained from the testing do not represent the same measurement.
PS is a DIN standard to measure engine power based on metric units. 1PS is equal to 75 kgm/second. This standard also measures net engine power and so while some differences in method exist between HP (SAE) and PS they can be considered directly comparable. While PS is the normally accepted label, preventing confusion with HP, one could write PS as HP providing they signify that its DIN or metric.
1PS does not equal 1HP due to the difference of the imperial/metric units. 550 ftlbs = 76.04 kgm and 75 kgm = 542.48 ftlbs
A Watt is the unit of Power used by science and engineering. Its an SI unit where 1W = 1 kg m^2/s^3
This is the unit that manufacturers (in Europe) are required to provide the rated net power for an engine in.
The conversion of kW to HP or PS by european car manufacturers is purely for marketing purposes. They feel that customers don't understand kW in relation to cars. As I already mentioned, were the power figure obtained in kW larger numerically than the PS or HP figure then I suspect they would be quite happy using it.
US manufacturers are not required to provide power ratings in kW so still do so in HP using the SAE test.
Ive seen a few european car manufacturers starting to refer to PS values as HP where previously they were very clear it was PS. They do still mention that HP is (DIN) somewhere in the small print but its not right beside the term as it should be.
If one were more cynical, they may think that its purely a cheat to get a few HP bump on the advertising sheet since PS is always slightly more than HP.
Gassing Station | Porsche General | Top of Page | What's New | My Stuff