BHP as a universal rating
13 February 2015, 08:35 AM
#1
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BHP as a universal rating
I figure i'll punt this one out to NSR just to see if anything comes of it.
Does anyone else find the modified car scenese penchant for using for using BHP as a universal rating value really ****ing irritating? It seems to pop up everywhere and it strikes me as a real dumbing down of what in it's own right can be some very interesting engineering.
You look at any thread about gearboxes on here as an example "oh that ones only good for 400bhp". No it's not, it will most likely have a torque rating. The fact one is propostional to the other is immaterial, the box will have been designed for a rated torque.
Same with injectors, "the STi pinks are good till x bhp". Again no they aren't, they'll be rated to Y CC/Min at a certain pressure. Only in the funny little world that is the modified car scene would an injector be discusses in terms of BHP.
Anywho, that's me done.
Does anyone else find the modified car scenese penchant for using for using BHP as a universal rating value really ****ing irritating? It seems to pop up everywhere and it strikes me as a real dumbing down of what in it's own right can be some very interesting engineering.
You look at any thread about gearboxes on here as an example "oh that ones only good for 400bhp". No it's not, it will most likely have a torque rating. The fact one is propostional to the other is immaterial, the box will have been designed for a rated torque.
Same with injectors, "the STi pinks are good till x bhp". Again no they aren't, they'll be rated to Y CC/Min at a certain pressure. Only in the funny little world that is the modified car scene would an injector be discusses in terms of BHP.
Anywho, that's me done.
13 February 2015, 08:55 AM
#2
So does that mean my 5 speed gearbox and 440bhp injectors will do 440 bhp init? And does the 5 stand for 5000bhp or should we be talking whp? Also I have a VF22 turbo does this mean I can like go Very Fast like 220 mph? It's a crazy world we live in 
13 February 2015, 09:00 AM
#3
It's only a simplification. You're right it's not strictly correct but as a yardstick it suffices for those not clued up. Injectors should be measured in cc/min and gearboxes in torque threshold, however bhp does have some proportional representation.
13 February 2015, 09:31 AM
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It's changed my approach on further tuning, as torque seems to be the biggest enemy of the WRX and biggest ally of the STI, it's worth noting that you can lower/raise bhp whilst raising/lowering torque through mainly the use of turbo.
13 February 2015, 09:58 AM
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Should WHP not be used over BHP.
And not cars but I used to have a truck that was 660bhp and about 4000nm but it's the bhp number that gets put on the side of the truck. . It seems to me although more so with trucks it should be torque we measure by instead, but especially with diesels.
And not cars but I used to have a truck that was 660bhp and about 4000nm but it's the bhp number that gets put on the side of the truck. . It seems to me although more so with trucks it should be torque we measure by instead, but especially with diesels.
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13 February 2015, 10:04 AM
#8
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Should WHP not be used over BHP.
And not cars but I used to have a truck that was 660bhp and about 4000nm but it's the bhp number that gets put on the side of the truck. . It seems to me although more so with trucks it should be torque we measure by instead, but especially with diesels.
And not cars but I used to have a truck that was 660bhp and about 4000nm but it's the bhp number that gets put on the side of the truck. . It seems to me although more so with trucks it should be torque we measure by instead, but especially with diesels.
dirty D's tend to use torque cos thats what their headline figure is lol
Problem is WHP in america is fly wheel and also doesnt seem to have the same calculation applied anyway.
Horse power at the wheels is prob best description, transmission loss is variable anyway, so could argue that the bhp figure people quote isnt accurate either.
Only true way to know what HP the engine is is to bench dyno it with controlled air in etc etc
13 February 2015, 10:24 AM
#9
cars and trucks are very different things.
dirty D's tend to use torque cos thats what their headline figure is lol
Problem is WHP in america is fly wheel and also doesnt seem to have the same calculation applied anyway.
Horse power at the wheels is prob best description, transmission loss is variable anyway, so could argue that the bhp figure people quote isnt accurate either.
Only true way to know what HP the engine is is to bench dyno it with controlled air in etc etc
dirty D's tend to use torque cos thats what their headline figure is lol
Problem is WHP in america is fly wheel and also doesnt seem to have the same calculation applied anyway.
Horse power at the wheels is prob best description, transmission loss is variable anyway, so could argue that the bhp figure people quote isnt accurate either.
Only true way to know what HP the engine is is to bench dyno it with controlled air in etc etc
The last time my car was mapped I was a bit underwhelmed at first as I watched the figures gradually moving upwards but still someway short of the 400+ the car was making before. Then the conversion from wheel power to engine power was made and suddenly the sun came out and everyone was smiling. The calculated figure was way up there. But actually, why bother? A tuned Impreza's engine power can easily be higher than, say, that of an M3 but power at the wheels may be somewhat less. Why bother doing the conversion when it's what happens at the wheels that matters?
13 February 2015, 10:26 AM
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cars and trucks are very different things.
dirty D's tend to use torque cos thats what their headline figure is lol
Problem is WHP in america is fly wheel and also doesnt seem to have the same calculation applied anyway.
Horse power at the wheels is prob best description, transmission loss is variable anyway, so could argue that the bhp figure people quote isnt accurate either.
Only true way to know what HP the engine is is to bench dyno it with controlled air in etc etc
dirty D's tend to use torque cos thats what their headline figure is lol
Problem is WHP in america is fly wheel and also doesnt seem to have the same calculation applied anyway.
Horse power at the wheels is prob best description, transmission loss is variable anyway, so could argue that the bhp figure people quote isnt accurate either.
Only true way to know what HP the engine is is to bench dyno it with controlled air in etc etc
I know it's a different thing with trucks but they use bhp when torque is the more important figure. I would think that that can also be applied to diesel cars and wouldn't be any more or less misleading than bhp is in petrol cars.
600bhp/500ft lb or 550bhp/600ft lb. I would think the second one would be quicker all equal else where but it would be the 600bhp that wins the pub bragging rights.
ps with more cars getting turbos these day and more than that elec motors becoming more popular does torque not make more sense than ever?
Last edited by Carnut; 13 February 2015 at 10:33 AM.
13 February 2015, 10:32 AM
#13
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Yeah, horse power at wheels is what l was thinking, I didn't realise that in the US WHP can sometimes means flywheel.
I know it's a different thing with trucks but they use bhp when torque is the more important figure. I would think that that can also be applied to diesel cars and wouldn't be any more or less misleading than bhp is in petrol cars.
600bhp/500ft lb or 550bhp/600ft lb. I would think the second one would be quicker all equal else where but it would be the 600bhp that wins the pub bragging rights.
I know it's a different thing with trucks but they use bhp when torque is the more important figure. I would think that that can also be applied to diesel cars and wouldn't be any more or less misleading than bhp is in petrol cars.
600bhp/500ft lb or 550bhp/600ft lb. I would think the second one would be quicker all equal else where but it would be the 600bhp that wins the pub bragging rights.
0-60 torque is more important, top speed bhp is more important is how i understand it
13 February 2015, 10:46 AM
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13 February 2015, 10:48 AM
#15
That's true but it makes no real sense as it's not a true comparison, certainly when comparing an AWD car with a RWD car. Transmission losses in the latter are considerably less than in the AWD system, so calculated engine power is meaningless.
13 February 2015, 11:09 AM
#16
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when have people ever made sence when asking for more power?
very few people can actualy use the power they have, go out on a race track with a pro and you'll realise how bad you are lol
How many cars are driving round with 500nhp thats for perhaps 10 seconds in a straight line before backing off?
But doesnt stop people wanting 600,,, lol
very few people can actualy use the power they have, go out on a race track with a pro and you'll realise how bad you are lol
How many cars are driving round with 500nhp thats for perhaps 10 seconds in a straight line before backing off?
But doesnt stop people wanting 600,,, lol
13 February 2015, 11:27 AM
#17
when have people ever made sence when asking for more power?
very few people can actualy use the power they have, go out on a race track with a pro and you'll realise how bad you are lol
How many cars are driving round with 500nhp thats for perhaps 10 seconds in a straight line before backing off?
But doesnt stop people wanting 600,,, lol
very few people can actualy use the power they have, go out on a race track with a pro and you'll realise how bad you are lol
How many cars are driving round with 500nhp thats for perhaps 10 seconds in a straight line before backing off?
But doesnt stop people wanting 600,,, lol
13 February 2015, 12:25 PM
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I'll use the gearbox thing as an example again, I'd quite like to know what the actual rated torque on the TY754 box is but all i ever seem to find is "oh it's only good for 400bhp". Which as you say is proportional but with out knowing the RPM/BHP at the actual time of failure, the statement "mine went when i was running 400bhp" is basically worthless.
13 February 2015, 01:35 PM
#22
Oh **** off
Yeah I know, it just annoys me as i'm an engineer (granted electrical) by trade and find a lot of the detail stuff rather interesting but the massive over simplification can make finding proper info quite difficult.
I'll use the gearbox thing as an example again, I'd quite like to know what the actual rated torque on the TY754 box is but all i ever seem to find is "oh it's only good for 400bhp". Which as you say is proportional but with out knowing the RPM/BHP at the actual time of failure, the statement "mine went when i was running 400bhp" is basically worthless.
Yeah I know, it just annoys me as i'm an engineer (granted electrical) by trade and find a lot of the detail stuff rather interesting but the massive over simplification can make finding proper info quite difficult.
I'll use the gearbox thing as an example again, I'd quite like to know what the actual rated torque on the TY754 box is but all i ever seem to find is "oh it's only good for 400bhp". Which as you say is proportional but with out knowing the RPM/BHP at the actual time of failure, the statement "mine went when i was running 400bhp" is basically worthless.
Personally my take is forget what other people say (albeit it may be good/viable info), when you personally break something or find it's reached it's full capacity then that's the limit.
13 February 2015, 02:15 PM
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Quote from an old contact who used to design dynos:
"Firstly I don't subcribe to the fixed overall % increase with increased wheel power. The resaon I say this is that the parts that do change with a greater power input such as the gearbox, diff, tyre (deformation change only) will only contribute around 3 - 5% of the total 'losses or drag' as measured/displayed on a roller style chassis dyno. Much of the losses aren't in fact losses, but unmeasured power requirements. At constant speed, power is calculated by measuring the torque reaction of the retarder which is trunnion mounted & the rpm @ which the torque is produced (P = Torque * RPM (roller rpm!) / 5252 or 9549 depending on imperial or metric measurments) However there is power required just to be able to turn over the rollers & retarder, windage of the retarder (which has rotors very similar to a centrifugal pump) boundary layer windage from the rollers, parasitic drag from bearings, seals & grease (same goes for the gearbox) etc. So just to be able to turn over the rollers requires power in itself that goes unmeasured by the retarder. The power unmeasured increases with speed in an exponential fashion. The other power losses (or drag as it is displayed on SUN/MAHA dyno's) is a combination of heat & noise from the tyres, gearbox, bearings etc, windage from rotating components such as wheels/tyres, brake disks, & shafts. Other factors which cause different drag/losses is the seperation of the rollers, those dyno's which have the rollers further apart cause greater drag, as the tyre deformation is greater, as it causes the tyre to be 'pinched' the same goes for smaller diameter rollers. The faster the 'road speed' the greater the losses, as the heat/noise losses goes up, as does windage of the afore mentioned parasitic absorbtions."
Lots of variables and unmeasured power requirements are not losses. One common source of a massive misrepresentation is where a 2WD car is not through the output of those two wheels also turning the undriven wheels and a second set of rollers. Otherwise you blame unmeasured power requirements of the dyno on the drivetrain of the AWD car.
"Firstly I don't subcribe to the fixed overall % increase with increased wheel power. The resaon I say this is that the parts that do change with a greater power input such as the gearbox, diff, tyre (deformation change only) will only contribute around 3 - 5% of the total 'losses or drag' as measured/displayed on a roller style chassis dyno. Much of the losses aren't in fact losses, but unmeasured power requirements. At constant speed, power is calculated by measuring the torque reaction of the retarder which is trunnion mounted & the rpm @ which the torque is produced (P = Torque * RPM (roller rpm!) / 5252 or 9549 depending on imperial or metric measurments) However there is power required just to be able to turn over the rollers & retarder, windage of the retarder (which has rotors very similar to a centrifugal pump) boundary layer windage from the rollers, parasitic drag from bearings, seals & grease (same goes for the gearbox) etc. So just to be able to turn over the rollers requires power in itself that goes unmeasured by the retarder. The power unmeasured increases with speed in an exponential fashion. The other power losses (or drag as it is displayed on SUN/MAHA dyno's) is a combination of heat & noise from the tyres, gearbox, bearings etc, windage from rotating components such as wheels/tyres, brake disks, & shafts. Other factors which cause different drag/losses is the seperation of the rollers, those dyno's which have the rollers further apart cause greater drag, as the tyre deformation is greater, as it causes the tyre to be 'pinched' the same goes for smaller diameter rollers. The faster the 'road speed' the greater the losses, as the heat/noise losses goes up, as does windage of the afore mentioned parasitic absorbtions."
Lots of variables and unmeasured power requirements are not losses. One common source of a massive misrepresentation is where a 2WD car is not through the output of those two wheels also turning the undriven wheels and a second set of rollers. Otherwise you blame unmeasured power requirements of the dyno on the drivetrain of the AWD car.
13 February 2015, 02:17 PM
#24
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If you launching and or changing at 5,000 rpm you are genuinely skipping the peak torque zone and getting to the point where elevated BHP gets you to the redline.
Torque is only good for casual overtaking in my opinion or fluffed gears.
My mates FWD car has 330lbft and it's unusable in 1st to 3rd gear. Great in 4th-6th but tbh I'd prefer less torque and to drop to 3rd to overtake and have a more usable 1st-3rd.
Like all things it's user preference.
13 February 2015, 02:39 PM
#25
Quote from an old contact who used to design dynos:
"Firstly I don't subcribe to the fixed overall % increase with increased wheel power. The resaon I say this is that the parts that do change with a greater power input such as the gearbox, diff, tyre (deformation change only) will only contribute around 3 - 5% of the total 'losses or drag' as measured/displayed on a roller style chassis dyno. Much of the losses aren't in fact losses, but unmeasured power requirements. At constant speed, power is calculated by measuring the torque reaction of the retarder which is trunnion mounted & the rpm @ which the torque is produced (P = Torque * RPM (roller rpm!) / 5252 or 9549 depending on imperial or metric measurments) However there is power required just to be able to turn over the rollers & retarder, windage of the retarder (which has rotors very similar to a centrifugal pump) boundary layer windage from the rollers, parasitic drag from bearings, seals & grease (same goes for the gearbox) etc. So just to be able to turn over the rollers requires power in itself that goes unmeasured by the retarder. The power unmeasured increases with speed in an exponential fashion. The other power losses (or drag as it is displayed on SUN/MAHA dyno's) is a combination of heat & noise from the tyres, gearbox, bearings etc, windage from rotating components such as wheels/tyres, brake disks, & shafts. Other factors which cause different drag/losses is the seperation of the rollers, those dyno's which have the rollers further apart cause greater drag, as the tyre deformation is greater, as it causes the tyre to be 'pinched' the same goes for smaller diameter rollers. The faster the 'road speed' the greater the losses, as the heat/noise losses goes up, as does windage of the afore mentioned parasitic absorbtions."
Lots of variables and unmeasured power requirements are not losses. One common source of a massive misrepresentation is where a 2WD car is not through the output of those two wheels also turning the undriven wheels and a second set of rollers. Otherwise you blame unmeasured power requirements of the dyno on the drivetrain of the AWD car.
"Firstly I don't subcribe to the fixed overall % increase with increased wheel power. The resaon I say this is that the parts that do change with a greater power input such as the gearbox, diff, tyre (deformation change only) will only contribute around 3 - 5% of the total 'losses or drag' as measured/displayed on a roller style chassis dyno. Much of the losses aren't in fact losses, but unmeasured power requirements. At constant speed, power is calculated by measuring the torque reaction of the retarder which is trunnion mounted & the rpm @ which the torque is produced (P = Torque * RPM (roller rpm!) / 5252 or 9549 depending on imperial or metric measurments) However there is power required just to be able to turn over the rollers & retarder, windage of the retarder (which has rotors very similar to a centrifugal pump) boundary layer windage from the rollers, parasitic drag from bearings, seals & grease (same goes for the gearbox) etc. So just to be able to turn over the rollers requires power in itself that goes unmeasured by the retarder. The power unmeasured increases with speed in an exponential fashion. The other power losses (or drag as it is displayed on SUN/MAHA dyno's) is a combination of heat & noise from the tyres, gearbox, bearings etc, windage from rotating components such as wheels/tyres, brake disks, & shafts. Other factors which cause different drag/losses is the seperation of the rollers, those dyno's which have the rollers further apart cause greater drag, as the tyre deformation is greater, as it causes the tyre to be 'pinched' the same goes for smaller diameter rollers. The faster the 'road speed' the greater the losses, as the heat/noise losses goes up, as does windage of the afore mentioned parasitic absorbtions."
Lots of variables and unmeasured power requirements are not losses. One common source of a massive misrepresentation is where a 2WD car is not through the output of those two wheels also turning the undriven wheels and a second set of rollers. Otherwise you blame unmeasured power requirements of the dyno on the drivetrain of the AWD car.
That's very interesting, and presumably a truly accurate measurement would only be achieved by an engine dyno. Even that must have its friction losses and consequential power distortions, and it would still not have any real relevance to the power going through the wheels to the road once it's re-installed. There would be the losses as noted, so how would you measure the power reaching the road (poor expression I know) without employing some form of dyno?
13 February 2015, 03:12 PM
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I would measure acceleration on tarmac. Not always practical.
Engine dynos are not a panacea either as the cooling and loading are often different. You can grossly misrepresent the spool up of an oversized turbo and tuners often do using engine dyno plots.
Engine dynos are not a panacea either as the cooling and loading are often different. You can grossly misrepresent the spool up of an oversized turbo and tuners often do using engine dyno plots.
13 February 2015, 03:48 PM
#27
So now we know what doesn't work particularly well. This presumably means that mappers, even the best, are working within fairly broad parameters to avoid getting too close to the 'you've had it!' line. Is there anything that does offer reasonable accuracy without resorting to F1-type budgets? Sorry for all the questions by the way.
13 February 2015, 04:12 PM
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Quote from an old contact who used to design dynos:
"Firstly I don't subcribe to the fixed overall % increase with increased wheel power. The resaon I say this is that the parts that do change with a greater power input such as the gearbox, diff, tyre (deformation change only) will only contribute around 3 - 5% of the total 'losses or drag' as measured/displayed on a roller style chassis dyno. Much of the losses aren't in fact losses, but unmeasured power requirements. At constant speed, power is calculated by measuring the torque reaction of the retarder which is trunnion mounted & the rpm @ which the torque is produced (P = Torque * RPM (roller rpm!) / 5252 or 9549 depending on imperial or metric measurments) However there is power required just to be able to turn over the rollers & retarder, windage of the retarder (which has rotors very similar to a centrifugal pump) boundary layer windage from the rollers, parasitic drag from bearings, seals & grease (same goes for the gearbox) etc. So just to be able to turn over the rollers requires power in itself that goes unmeasured by the retarder. The power unmeasured increases with speed in an exponential fashion. The other power losses (or drag as it is displayed on SUN/MAHA dyno's) is a combination of heat & noise from the tyres, gearbox, bearings etc, windage from rotating components such as wheels/tyres, brake disks, & shafts. Other factors which cause different drag/losses is the seperation of the rollers, those dyno's which have the rollers further apart cause greater drag, as the tyre deformation is greater, as it causes the tyre to be 'pinched' the same goes for smaller diameter rollers. The faster the 'road speed' the greater the losses, as the heat/noise losses goes up, as does windage of the afore mentioned parasitic absorbtions."
Lots of variables and unmeasured power requirements are not losses. One common source of a massive misrepresentation is where a 2WD car is not through the output of those two wheels also turning the undriven wheels and a second set of rollers. Otherwise you blame unmeasured power requirements of the dyno on the drivetrain of the AWD car.
"Firstly I don't subcribe to the fixed overall % increase with increased wheel power. The resaon I say this is that the parts that do change with a greater power input such as the gearbox, diff, tyre (deformation change only) will only contribute around 3 - 5% of the total 'losses or drag' as measured/displayed on a roller style chassis dyno. Much of the losses aren't in fact losses, but unmeasured power requirements. At constant speed, power is calculated by measuring the torque reaction of the retarder which is trunnion mounted & the rpm @ which the torque is produced (P = Torque * RPM (roller rpm!) / 5252 or 9549 depending on imperial or metric measurments) However there is power required just to be able to turn over the rollers & retarder, windage of the retarder (which has rotors very similar to a centrifugal pump) boundary layer windage from the rollers, parasitic drag from bearings, seals & grease (same goes for the gearbox) etc. So just to be able to turn over the rollers requires power in itself that goes unmeasured by the retarder. The power unmeasured increases with speed in an exponential fashion. The other power losses (or drag as it is displayed on SUN/MAHA dyno's) is a combination of heat & noise from the tyres, gearbox, bearings etc, windage from rotating components such as wheels/tyres, brake disks, & shafts. Other factors which cause different drag/losses is the seperation of the rollers, those dyno's which have the rollers further apart cause greater drag, as the tyre deformation is greater, as it causes the tyre to be 'pinched' the same goes for smaller diameter rollers. The faster the 'road speed' the greater the losses, as the heat/noise losses goes up, as does windage of the afore mentioned parasitic absorbtions."
Lots of variables and unmeasured power requirements are not losses. One common source of a massive misrepresentation is where a 2WD car is not through the output of those two wheels also turning the undriven wheels and a second set of rollers. Otherwise you blame unmeasured power requirements of the dyno on the drivetrain of the AWD car.
You cant just measure the engine by itself because you then have gear boxes etc to take into consideration, so we need dynos for testing the end result,ie road worthy cars.
So given we need to see how the full package works together surely measuring the power at the end result once gone through the gearbox etc is the closest we can get and a improvement over BHP that's guessed?
Plus the losses from dynos as mentioned above, are they not outweighed by wind resistance etc on the road, kinda tit for tat?(we just need a good bench mark)
13 February 2015, 04:46 PM
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So now we know what doesn't work particularly well. This presumably means that mappers, even the best, are working within fairly broad parameters to avoid getting too close to the 'you've had it!' line. Is there anything that does offer reasonable accuracy without resorting to F1-type budgets? Sorry for all the questions by the way.
13 February 2015, 04:50 PM
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You cant just measure the engine by itself because you then have gear boxes etc to take into consideration, so we need dynos for testing the end result,ie road worthy cars.
So given we need to see how the full package works together surely measuring the power at the end result once gone through the gearbox etc is the closest we can get and a improvement over BHP that's guessed?
Plus the losses from dynos as mentioned above, are they not outweighed by wind resistance etc on the road, kinda tit for tat?(we just need a good bench mark)
So given we need to see how the full package works together surely measuring the power at the end result once gone through the gearbox etc is the closest we can get and a improvement over BHP that's guessed?
Plus the losses from dynos as mentioned above, are they not outweighed by wind resistance etc on the road, kinda tit for tat?(we just need a good bench mark)
Dyno losses are of a different nature to wind resistance and not simply exchanged or written off so easily.