hard on u, thanks for such great info.Originally posted by STiYaKuzA:ahh got a graph of the WRX STi twin turbo version
in the graph, the red line represents the horsepower in kW which shows a maximum rating of around 206kW(280hp) at 6000rpm. the blue line shows the torque rating in newton metre, which shows a maximum of 394Nm(40.2kgm) at 4400rpm. for power curve, it would be good if the max. power is at a higher rpm, but for torque, u would want the rpm to be lower. if the rpm is higher for the power curve, it means a higher top speed. however, if the torque curve rpm is high, it means the car would take longer to accelerate to its max. rate of acceleration. therefore, a lower rpm would be good for the torque curve(to bring the car to its max. rate of acceleration faster and therefore bringing it to the top speed faster). so if u have an engine which has 1000hp but 1kgm of torque, it would take ages to reach the top speed. as u can see, the point of intersection does not indicate the best rpm to shift gears, as at that time the car would have been almost deprived of torque(by right, the car will not be able to exceed 6000 rpm at gear 6 & high speed due to air resistance and other reaction forces. in lower gears like 1 & 2, it would still be possible to exceed 6000 rpm as the reaction forces are not that great yet). therefore i would say that the optimum rpm to change gear is around 5500rpm as the torque is still quite plentiful. and i doubt there is any graph that does not show any intersection. even if they do not show, the two would intersect sooner or later, as it is impossible for the two to stay at optimum forever
. btw this is quite a bad engineering, as it forces u to change gears at an rpm which is not optimum yet... usually NA cars like the NSX would have better intersection(almost near peak of both curves). i would try to find one and compare the differences
thanks! thanks for helping me find the graph n explain. hee i can relax liao.Originally posted by STiYaKuzA:ahh got a graph of the WRX STi twin turbo version
in the graph, the red line represents the horsepower in kW which shows a maximum rating of around 206kW(280hp) at 6000rpm. the blue line shows the torque rating in newton metre, which shows a maximum of 394Nm(40.2kgm) at 4400rpm. for power curve, it would be good if the max. power is at a higher rpm, but for torque, u would want the rpm to be lower. if the rpm is higher for the power curve, it means a higher top speed. however, if the torque curve rpm is high, it means the car would take longer to accelerate to its max. rate of acceleration. therefore, a lower rpm would be good for the torque curve(to bring the car to its max. rate of acceleration faster and therefore bringing it to the top speed faster). so if u have an engine which has 1000hp but 1kgm of torque, it would take ages to reach the top speed. as u can see, the point of intersection does not indicate the best rpm to shift gears, as at that time the car would have been almost deprived of torque(by right, the car will not be able to exceed 6000 rpm at gear 6 & high speed due to air resistance and other reaction forces. in lower gears like 1 & 2, it would still be possible to exceed 6000 rpm as the reaction forces are not that great yet). therefore i would say that the optimum rpm to change gear is around 5500rpm as the torque is still quite plentiful. and i doubt there is any graph that does not show any intersection. even if they do not show, the two would intersect sooner or later, as it is impossible for the two to stay at optimum forever
. btw this is quite a bad engineering, as it forces u to change gears at an rpm which is not optimum yet... usually NA cars like the NSX would have better intersection(almost near peak of both curves). i would try to find one and compare the differences
Good explanation but i believe the optimum rpm to change gear is at 4400 (using your graph) since it is the time when max torque is released.Originally posted by STiYaKuzA:ahh got a graph of the WRX STi twin turbo version
in the graph, the red line represents the horsepower in kW which shows a maximum rating of around 206kW(280hp) at 6000rpm. the blue line shows the torque rating in newton metre, which shows a maximum of 394Nm(40.2kgm) at 4400rpm. for power curve, it would be good if the max. power is at a higher rpm, but for torque, u would want the rpm to be lower. if the rpm is higher for the power curve, it means a higher top speed. however, if the torque curve rpm is high, it means the car would take longer to accelerate to its max. rate of acceleration. therefore, a lower rpm would be good for the torque curve(to bring the car to its max. rate of acceleration faster and therefore bringing it to the top speed faster). so if u have an engine which has 1000hp but 1kgm of torque, it would take ages to reach the top speed. as u can see, the point of intersection does not indicate the best rpm to shift gears, as at that time the car would have been almost deprived of torque(by right, the car will not be able to exceed 6000 rpm at gear 6 & high speed due to air resistance and other reaction forces. in lower gears like 1 & 2, it would still be possible to exceed 6000 rpm as the reaction forces are not that great yet). therefore i would say that the optimum rpm to change gear is around 5500rpm as the torque is still quite plentiful. and i doubt there is any graph that does not show any intersection. even if they do not show, the two would intersect sooner or later, as it is impossible for the two to stay at optimum forever
. btw this is quite a bad engineering, as it forces u to change gears at an rpm which is not optimum yet... usually NA cars like the NSX would have better intersection(almost near peak of both curves). i would try to find one and compare the differences
Originally posted by Red Lobster:dunno about the link but i think u've offered a pretty comprehensive explaination about torque n bhp. well done!
I've always been confused about the concepts of torque & horsepower, so did some research on google.
Torque and hp are not really intuitive to grasp, and here are some of the easier-to-understand links I've found:
http://www.nissanperformancemag.com/november98/torque.shtml
http://www.allpar.com/eek/hp-vs-torque.html
http://vettenet.org/torquehp.html
Essentially, the articles come to the same conclusion as many of you have mentioned - torque is responsible for acceleration (how hard your head is thrown against the seat when you floor it), while hp is a representation of how much torque your engine can produce at high rpms - and would be more important for top speed.
They say that torque and hp are mathematically related by the formula:
Hp (bhp) = Torque (lbs.ft) x rpm / 5252 (if torque is given in US units) OR
Hp (bhp) = Torque (Nm) x rpm / 7023.5 (if torque is given in Nm)
I think this means that the max torque & hp specs we read so often are basically 2 snapshot views of an engine's torque curve, at different rpms. The max torque shows the engine's peak torque, which happens at a certain rpm level, while the max hp indicates how much torque it can pump out at a higher rpm.
Eg. Car A has max torque of 145Nm at 4000rpms & max hp of 100bhp at 6500rpms. From the formula, when the car is generating max hp at 6500rpms, it is pushing out [b]108Nm of torque.
Car B has same max torque of 145Nm at 4000rpms but higher max hp of 120bhp at 6500rpms. From the formula, Car B is pushing out 130Nm at 6500rpms. So Car B can accelerate harder at 6500rpms than Car A, although they accelerate just as hard at 4000rpms.
The formula also means that all hp-torque charts will always intersect at 7023.5rpm, IF the units are given in bhp and Nm, AND the scales are the same, regardless of car, engine, tuning, TC or NA.
The articles go on to recommend that its better to upshift at redline, rather than anywhere else based on the shape of the curves.
What do you guys think of the analysis given in the links? [/b]