Engine Talk

[eVo-XTreme]

Hmmm... does an engine with a maximum power of 118/5,500 (ps/rpm) faster compared to an engine with 118/6,200 (ps/rpm)??? San ba nalalaman kung ang engine ng isang car eh malakas or mabilis? Sa displacement lang ba ng engine? ^_^

[speedyfix]

power at a lower rpm will make the car feel faster because you will feel the acceleration earlier.

[eVo-XTreme]

i thought no one would ever try to reply on this post.. hehe... so speedefix, will a car with a lower rpm also affect its top speed?

[yebo]

alam mo medyo complicated yan question mo. are you asking same car with different engine and tranny installed or completely different cars?

kung same car with different engine and tranny, then they MAY have the same top speed since the weight, coefficient of drag, frontal area, tyre size and type, etc etc etc are the same. it will finally rest on the final drive ratio from engine-tranny-differential. IF the final drive ratio are the same then the higher speed engine MIGHT deliver a higher top speed ON THE ASSUMPTION that the power delivered is enough to propel the car to that higher top speed. but most of the time the higher revving engine will be mated to a higher drive ratio tranny and differential so the top speeds will not differ much.

if you're comparing different cars then there are as many possible answers to your question as there are car models. you can't possibly compare apples and peaches.

[eVo-XTreme]

Originally posted by yebo
alam mo medyo complicated yan question mo. are you asking same car with different engine and tranny installed or completely different cars?

kung same car with different engine and tranny, then they MAY have the same top speed since the weight, coefficient of drag, frontal area, tyre size and type, etc etc etc are the same. it will finally rest on the final drive ratio from engine-tranny-differential. IF the final drive ratio are the same then the higher speed engine MIGHT deliver a higher top speed ON THE ASSUMPTION that the power delivered is enough to propel the car to that higher top speed. but most of the time the higher revving engine will be mated to a higher drive ratio tranny and differential so the top speeds will not differ much.

if you're comparing different cars then there are as many possible answers to your question as there are car models. you can't possibly compare apples and peaches.

ganun po ba? hehe... sorry! medyo curious kasi ako when it comes to cars lalo na with their engines... i also like comparing different kinds of vehicles with one another... kaya siguro napakcomplicated na ng question ko... hahahaha! im just just a kid you know? LOLS! pero kung sa bagay, there are pros and cons on different engines.. am i right? anyway, bout the 2 engines im comparing with... 2 different cars ang tinutukoy ko... ^_^

[mazdamazda]

to better gauge the performance of the engine that you are referring to, maybe you can take a look at the following:

- hp / ps output over the whole rpm band. or a dyno chart.
- performance for 0-60kph, 60-100kph, 0-100kph, 100kph-160kph, 0-160kph.

[pepengtom]

anong kotse ba ung kinocompare mo?

[ebbfolls]

Power is power, regardless of where in the rpm band it is found. Given 2 engines of the same power output, and both of these engines are fitted into very similar cars, mated to transmissions that are geared appropriately so that the same amount of roadwheel horsepower(rwhp) is made at the driving wheels, then both cars will have the same performance, though they may sound different by reason of the 2 different torque and hp curves.

However, theoretically, the engine with the higher rpm will have less frictional losses through the driveline by reason of the lower gears it will be using, thus giving it a negligible power advantage over the other engine.

[speedyfix]

i think nagkakagulo and nagiging masyado complicated na itong thread.

basically you just need to know that if 2 engines make the same power at dfferent points, all other things being equal, then the one making it at lower rpm's will feel faster.

however, since in the real world not all things are equal and you have to take into consideration things like the weight of the car, gearing of the tranny, weight of the flywheel (how fast it revs), and a whole bunch of other stuff including torque and where that peaks, it will be hard to do a comparo by just looking at the stats.

i think they call this bench racing wherein you just look at the numbers and extrapolate data from there (i.e. if i do this to the engine, ito yung magiging gains ko and so on). well, using this is not the best means to see whether a car is faster than another or not kaya testing and a heads up comparison is always key

whew!

[ebbfolls]

To the threadstarter who wanted to know kung pano malalaman ang lakas ng engine-- sa POWER rating po yun. Power is the ability to produce work(or results) per a given amount of time.

Horsepower(HP) = Torque X RPM/5252



Mr. Speedyfix,

You are right about your argument about the variables being virtually impossible to control, as to make a valid test between 2 different engines. But in theory, 2 engines making the same amount of power, regardless of what rpm they make their max power, are equally POWERFUL one to the other. 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.)

So, if both engines are made to power cars of the same weight, both cars will have the same acceleration times and top speeds, because they are being propelled forward by engines that have the same amount of capacity to do work.

However, since you mentioned flywheel weight, then that would also have to be put nto consideration if we are to talk about acceleration. The engine with the less rotational mass(moment of inertia), will of course be able to accelerate quicker (By the way, a lighter flywheel only means the engine will be able to accelerate quicker to a certain rpm, but max rpm is still a function of the torque band, regardless of flywheel weight). However, top speed still be the same because both engines will only be able to accelerate to the point at which they can no longer produce more power to push the car against the resistance of the air and other frictional forces.