Lets forget about rpm, torque peak, and engine.

From physic point of view, in layman term:

Torque = ability to carry load
High torque means high load bearing ability. Low load bearing ability means a vehicle will immediately feel sluggish when a load is added.

Horsepower = ability to accelerate[/u]
High horsepower means better acceleration. For a vehicle with same load, high horsepower means it accelerate better.

Ok, now lets get complicated. A vehicle with small torque but huge horsepower has amazing acceleration. But any additional load will make significant impact on its acceleration, because the inability to handle load (due to low torque). For example, motorbike.

Then, a vehicle with huge torque but small horsepower has low acceleration, but excellent load handling. By load handling means, the vehicle won't feel much different when a load is added. For example, bulldozer.

When it comes to good engine management (and driving experience), race car driver generally drive the car at high rpm near peak hp. While truck driver generally drive the vehicle around peak torque.

Now lets take a real scenario. Say a car with peak torque at 4k rpm and peak hp at 6k rpm.

During uphill drive, when engine speed drop below peak torque (say 3k rpm), the engine immediately feel sluggish. Hence we downshift, accelerate (rev) the engine to higher rpm, say to 5k rpm (higher than peak torque). After that, when we shift the gear back, say 4k, we immediately feel the engine power returns.

The sames goes to why tires are more likely to burn (skid) when we accelerate from standstill at peak hp.

As i know the horsepower constantly increase when RPM roll up,n normally would achieve peak HP at 6-7K RPM.
Is tat means for fastest acceleration,we should drag to 6-7k RPM b4 shift to higher gear?

For example:
we drag the 1st gear to 7k RPM to archieve Peak Horse power,
Then shift up to 2nd gear n the RPM dropped to 5k RPM,then we drag again to 7k RPM to Peak horse power,
N repeat n repeat...
So in this way we can maintain the peak HP,n btw Fastest acceleration?

I dun think all these make sense,torque is the force to twist the wheel/tyre,meaning torque high=faster acceleration,
Peak HP should be the total force created at by the car wheel at maximum RPM,meaning a metric for topspeed.

This post has been edited by nujo87: Dec 8 2009, 12:47 AM

out of topic: no leh.. for city campro sucks because u have to rev it high.. get torque only after so much revving... for highway also it sucks because @ 120km/h it has to be rev high also... so it is totally =.=" this kind of tech is around 20 years old already, even if it has valve tech which provides flatter torque curve... newer tech are like those by vw... small turbo charged engines.. good fc good performance... tdsi fsi

no no.. d best fc is obtain by the fastest speed at the highest gear reachable by the peak torque... knowing just the speed and rpm wont tell much

i didnt say u r a idiot also.. dun get offended... me n u just trying to share... ok, i get what u r trying to convey... but if u were to compare d 3 cays then maybe car no. 2 not nessesary get d best fc.. but i get what u mean about d torque band

horsepower depends on rpm because hp depends on speed which depends on wheel speed...if the torque is high, but the wheel spins then actual hp will be less because d wheel is losing traction.. unless u r talking about dyno hp.. am i right?

ermm.. for the example it depends on the car... whether is it na/turbo.. gear ratios/torque curves,top speed... the best i believe for na sporty cars (eg integra) (from personal experience) is to rev to max, shift and it will drop to just slightly below max torque.... it depends on d gear ratios...



i believe what you say is true... that's what i learned during dynamics

Then blame the transmission not the engine Poor pairing of transmission with engine will make any engine no matter how good perform poorly
I thought that was pre-assumed from my analysis I gave the speed as an example to show where the savings comes from, when you go faster, u spend les time on the road running the engine

no leh.. their transmission no prob.. just that they follow d wrong trend... they still think techs like vvti, vtec vvtc are d best around... so hard spend so much $$$ for their cps then they realise oops... there's a better tech around owned by vw...

An old article I read that debated shifting at peak torque vs shifting at max HP explained it this way:
1. Say you shift at peak torque, when you go to the next higher gear, your engine torque now is lower than what you had earlier because it is revving at lower rpm. The engine has to climb up the torque mountain again, thus giving poorer acceleration
2. As you know, the torque usually peaks at around 2000-4000rpm and then starts dropping. Now if you shift at max HP or redline, you will definitely be shifting to an rpm where your torque is higher than it was before. The acceleration will be better.

Conclusion: always shift close to max power to obtain best acceleration

cps not that bad also if you ever try b4, the performance have a drastic improvement compared to campro without cps.

and transmission does matter alot. first generation gen2 with automatic gearbox just simply lower the gear when u approach a slightly downhill, and when u floor the acceleration pedal it takes much longer time to lower the gear. dun you think it ll affect the performance and fuel consumption alot.

hahah.. out of topic la bro..

but d world is no longer playing with valve timing anymore... that was like 20-30 years ago... now compare it with the fsi and tsi engines... superior fc & performance for small engines... or even hybrids

lol... that 1 is gearbox prob... not design prob... so they design it with a lousy gearbox is a diff story

Lets say for car 1,torque peak at 2500RPM,and slowly drop from 2.5k-4k,n a drastic drop after 4k.
Which way should be better?

1)drag to 4k RPM n then shift to higher gear,n it should drop back to 2-3k RPM.

2)drag to 6k RPM(closest to MAX HP)then only shift gear,n should be dropped to 4-5k RPM.

he already explained that the best would to rev it as high as the engine is designed to..

Seriously do u guys think,if i go to a car showroom,do i have the RIGHT to ask for their engine torque curve/HP curve chart?
Or any other way to know a car engine performance more detail?

Buy car not = buy something in pasar le

This post has been edited by nujo87: Dec 8 2009, 01:56 PM

they should have it... unless u r looking for local cheap cars... eg from peroduas... why bother

If Sir Isaac Newton is still alive, he would have been struck with heart attack after reading the postings in this thread. If only electric motor has been discovered back then this question wouldn't have been asked int he first place. Where efficiency is high, often greater than 0.9 this issue is a matter of dust. Absolutely bin material if you asked me.

Regards, Joey

p.s: Torque and power are (almost) flip sides of the same coin. They are entwined entities.

This post has been edited by Joey Christensen: Dec 8 2009, 05:22 PM

dun care la wut the theory is.. pedal to metal = win

What exactly is the point of your reply? where does this connect with the importance of torque or horsepower in a vehicle?

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Added on December 8, 2009, 8:36 pmpedal to metal = hole in pocket

This post has been edited by joe_star: Dec 8 2009, 08:36 PM

Hmm, I have to disagree with you. (No offense, but this is what phd section is all about: argument and discussion ) In fact, motor is a perfectly good example of how engine can be so different. I'll drop the efficiency factor, since this is a discussion about torque and horsepower.

Torque
Torque is the resultant of inertia x angular acceleration.

Horsepower
Horsepower (or power) is the rate of energy release. High horsepower means high rate of energy release. Like explosion.
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Motor
Motor has a constant (or near constant) torque with respect to RPM. Torque depends on voltage. While its power (or horsepower) depends on current draw (assume constant voltage). A motor with low resistance has high power rating. Motor power rating is also constant (due to constant resistant).

For example, take table fan. Without the blade, when we turned it on, the motor spin to its maximum speed almost immediately. And when we put on the blade, (higher inertia), the motor take some times to reach its maximum speed. Probably you also notice that fan with blade does not spin as fast as without. This is because air resistance increase as the speed increase. My last post use the assumption of fixed torque and power over the range, i.e. like a motor. Or more precisely, the instantaneous response (if you take dynamic, you know what I mean).

Engine
Engine, on the other hand has variable torque and horsepower. This is because its power input varies. (Motor has fixed power supply). Everyone knows engine runs due to small explosion in combustion chamber. And this combustion is not limited. (because someone "pedal to metal ").

In layman term, with fix fuel supply (maintain pedal position), a vehicle can travel at 100km/h (2500 rpm) on straight road, or 120km/h (3000 rpm) going downhill, or 70 km/h (2000 rpm) going uphill. Despite the different in speed and rpm, the engine actually consume same amount of fuel (in reality this might varies a bit, but this assumption is still generally true). What happen is that, the engine require less fuel to produce same amount of torque (during downhill) or more fuel during uphill.

Horsepower, on other hand, is the ability of the engine to response to fuel supply. (rate of energy release). An engine with high horsepower has the ability to response immediately to fuel, thus able to change its torque. By the chart, it simply means the ability to rev. If you notice, a car rpm increase faster when it approach peak hp, and fastest at peak hp. (We are unlikely to admit that it is fastest at peak hp. This is because hp drop after the peak hence it appear slow). Engines with VTEC, VVTI, CPS has higher peak hp at high rpm, this means driver will observe that the acceleration is highest when it reach peak hp.

What happen to campro engine, it has relatively acceptable hp chart (higher rate of energy release), which means angular acceleration (the speed rpm needle increase) is fairly constant. Because horsepower means the ability to change its torque, looking from the graph (campro), at 2000-3500 rpm, it means the ability to decrease its torque. This also mean it is less efficient in this interval. No wonder why campro owner complain about sluggish engine response. This effect is magnified during uphill. The dip in torque means it require even more fuel than other vehicle to carry itself uphill.

Back to motor, its high torque, low horsepower means it is good for road cruising, at constant speed. While for acceleration, the high horsepower engine comes in. The next generation of hybrid car will see the evolution of small cc engine (with high horsepower) and high torque motor.

How it is implemented, that require a new chapter of applied physic.

All this theory is good. but if u cant apply. its all just talk and no meaning...

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Added on December 9, 2009, 10:28 amPlease refer to my post script. It's already has it's meaning there and then.

Regards, Joey

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Added on December 9, 2009, 10:30 am

I wouldn't take it too far. Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context.

Regards, Joey



This post has been edited by Joey Christensen: Dec 9 2009, 10:30 AM

u pick it out of the text book ar? what you say is true.. that's what i am trying to explain... but u clear a lot of things up

however at the ending, bear in mind that doesnt take into acc of static acc... it is only after there's some movement the last paragraph applies.. that's why it is motor as motor has less static resitance, not engine... but the title is car

Getting more confused....
More layman's term pls

This post has been edited by nujo87: Dec 9 2009, 12:05 PM