Engine Talk

[eVo-XTreme]

*sighs*... super wala na akong maintindihan dito... wehehehe! pero like what ebbfolls said "Now, say a Toyota 2.0 liter is making 160 HP at 5000 rpm and a Honda 2.0 liter is making 160 HP at 7000 rpm. Both engines are of the same power, thus both are capable of doing the SAME AMOUNT OF WORK, at the SAME AMOUNT OF TIME. (But because their max power figures occur at different engine speeds, both have different TORQUE figures at the rpm where they both make their maximum power. But torque only tells about how strong an engine is without regard for time, while HP tells about how fast an engine can produce results.)"... kahit magkaiba ng max RPM ang isang car kahit pareho ng displacement, both are capable of doing the same amount of work at the amount of time... and the weight of the car also affects acceleration times and top speeds.... hehehe! now im quite enlightened with that answer... Thanks PEEPS! And just as i said... im just TOO curious about car engines... as in tagal ng umiikot sa utak ko ang question na yan... ^_^

[yebo]

Originally posted by eVo-XTreme
[B... as in tagal ng umiikot sa utak ko ang question na yan... ^_^ [/B]

wag mo masyado paikutin pards, dami na nadale dyan hehehe!

[kinyo]

the power vs. rpm curve of an engine looks like an inverted parabola, while load curve (required hp vs car speed) would look like the right-half of an upright parabola ... if the two curves were drawn on the same graph (with appropriate conversion of rpm into speed at highest gear), the top speed would then be the intersection of the two curves

if we now assume that the two engines' power curves have similar shape except that one's peak power occurs earliear than the other, then it can be concluded that the engine with higher rated rpm will have higher top speed ... but it can be expected that the difference in top speed would be minimal because the load curve is typically very steep at high speed

[eVo-XTreme]

Originally posted by yebo
wag mo masyado paikutin pards, dami na nadale dyan hehehe!

hahaha.... malapit na... LOLZ! ^_^

Mr. kinyo... thanks for the graph!

[ebbfolls]

Interesting concept.

What happens if the load curve is moved to the left so that it intersects both power curves before their power peaks?

[ian_rex]

in a sense yes. depende kung ano bang hanap mo. if you want acceleration, mas mabilis yung 118hp *5,500rpm but beyond that wala na kumpara sa 118hp *6200 rpm. pero sa top speed, i go for the latter kasi mas malaki ang power band nya kesa dun sa nauna, considering na pareho lang sila ng output.

based on my experience, mas maganda yung nasa top end ng rpm yung power para malaki ang power band. lalo na yung sa torque. sa diesels ganyan ang lakas ng torque kaya lang sa low to mid rpm lumalabas kaya pag sa long drive na high speed mabagal sya. pero matipid.

[kinyo]

Originally posted by ebbfolls
Interesting concept.

What happens if the load curve is moved to the left so that it intersects both power curves before their power peaks?

Then Engine A will end up with higher top speed.

The question now would be ... "What happens to the remaining HP that both engines are capable of generating? Won't that extra HP supposed to increase the speed further?"

The answer is "No". At any speed before the top speed is reached, the difference between the load curve and an engine's power curve is the HP being used to accelerate the car. When top speed is reached, acceleration becomes zero, speed becomes constant. Beyond the top speed, the load curve becomes higher than an engine's power curve, which means that any increment in speed requires more HP than the engine could produce for the same speed increment. Hence, the extra HP from an engine cannot be used to further accelerate the car and pressing on the pedal further would only result to waste.

Moving the load curve to the left might be akin to changing the aerodynamics of the car where wind drag is increased. If we deploy a parachute on the rear of the car, its top speed would be severely limited and pushing the engine further would only waste the tires while speed remains constant.

[ebbfolls]

Originally posted by kinyo
Moving the load curve to the left might be akin to changing the aerodynamics of the car where wind drag is increased. If we deploy a parachute on the rear of the car, its top speed would be severely limited and pushing the engine further would only waste the tires while speed remains constant.

It would also be akin to using a small displacement, high rpm engine to power a vehicle with a relatively large frontal area.

Using the appropriate reduction gearset would also bring the engines power peak closer to the load curve slightly improving the vehicle's top speed, dont you think? But I think this only applies to situations where the load curve intersects the power curve before max power peak.

[ebbfolls]

I've plotted a graph similar to the one you posted. This is the power output of the same engine measured at the output end of 2 reduction gear ratios. As can be seen, both power curves have the same HP levels as power does not change regardless torque reduction or multiplication, assuming negligible friction.

It's interesting to note how the difference between the HP requirement and the HP output of the engine is much greater with the lower gear from Point A to Point B. Points C and D, on the other hand, point to the increase of the top speed afforded by the taller gear.

The 'area under the curve' should probably equate to energy expenditure.

You are welcome to correct any misconceptions.


(Sorry, that didnt work. How do you paste a picture here anyway?)

[kinyo]

Use the "New Reply" button. You will then see the "Attach file" feature.