very basic car question

[edde]

An engine that produced the same power from 2000 rpm through to 6000 rpm would only be producing a third as much torque at 6K than it was at 2K. So at 6K it would only be producing a third as much pushing force at the wheels to accelerate the vehicle, and the rate of acceleration would only be a third as much. However if it had a flat torque curve from 2K right through to 6K it would produce constant acceleration, but that'd require it producing three times as much power at 6K than at 2K.

It might only be making 1/3 the torque but three times the speed o its the same HP same acceleration. The gearing would have to be adjusted to show it.

The second engine you on about with a flat torque curve accelerates faster at higher rpm as its hp which actually accelerates you.

 

[GordonD]

The second engine you on about with a flat torque curve accelerates faster at higher rpm as its hp which actually accelerates you.

F=ma
a=F/m
It is not power that accelerates you, it is force, in this case engine torque converted to tractive force by whichever of the car's tyres are driven.
Ek=1/2.mv^2
Power doesn't accelerate you, it adds to your kinetic energy, and that goes up with the square of speed, so a constant amount of power doesn't produce as high a rate of change of speed (acceleration) at a higher speed as it does at lower speeds.

You are a knowledgeable and competent advisor to the posters of this forum on matters mechanical Edde, far more so than I could be, but your expertise clearly doesn't include physics.

 

[Mells]

F=ma
a=F/m
It is not power that accelerates you, it is force, in this case engine torque converted to tractive force by whichever of the car's tyres are driven.
Ek=1/2.mv^2
Power doesn't accelerate you, it adds to your kinetic energy, and that goes up with the square of speed, so a constant amount of power doesn't produce as high a rate of change of speed (acceleration) at a higher speed as it does at lower speeds.

You are a knowledgeable and competent advisor to the posters of this forum on matters mechanical Edde, far more so than I could be, but your expertise clearly doesn't include physics.

I still love you eddie!

 

[stan*]

He's right Edde lad...

Torque from the engine/transmission gives tractive effort at he driving wheels. this exerts a force on the road, which exerts an opposite force. Net acln is related to the difference in force exerted by the two bodies.

Mathematically...(as above) A=F/m

TE It is also influenced by tyre radius...hence slower acln with larger overall wheel/tyre size.

 

[stan*]

However its worth noting...

If in the case of the flat torque curve yielding "constant accleration"...it wouldnt strictly be constant in practice. Wind resistence will increase with velocity, therefore the opposing force increases with V, so accln decreases. strictly speaking!

 

[stan*]

lol...also...strictly speaking...

never mind!

 

[edde]

I'm to confused by now.
I'm right about the engine bit 200hp is 200hp same acceleration regardless of rpm I'm sure.

 

[stan*]

tbh mate i havnt read the whole thread, and im not quite sure what u mean. if u can explain some more...

 

[edde]

tbh mate i havnt read the whole thread, and im not quite sure what u mean. if u can explain some more...

I think earlier somone suggested a car


To be honest lots of people mis-understand the relationship. You see high RPM is good because you can run lower gears, which make the wheels easier to turn, so increase acceleration. Which is why diesels with monster torque at low revs still accelerate relatively slowly (due to high gearing).


I'm disagreeing saying it doens't matter its the Hp at the wheels which matter doesn't matter if the engine has 10 million pounds of torque at 10rpm or 10 million rpm and 10lb of torque they will both go as quick.

 

[jiminy]

I'm to confused by now.
I'm right about the engine bit 200hp is 200hp same acceleration regardless of rpm I'm sure.

i think you need to withdraw the word acceleration from that statement because that confuses the issue as acceleration is dependant on so many things.

but if your car produces 200hp at 3000rpm or 7000rpm, you are putting the same amount of power into a system. you will get the same acceleration if all the other variables are the same

 

[stan*]

Power is a function of torque and speed...so those two extreme examples would yield different power output.

 

[stan*]

i think you need to withdraw the word acceleration from that statement because that confuses the issue as acceleration is dependant on so many things.

but if your car produces 200hp at 3000rpm or 7000rpm, you are putting the same amount of power into a system. you will get the same acceleration if all the other variables are the same

Nope...we've already established torque brings accln!

IF an engine produced 200bhp at 3000rpm AND 7000rpm....the torque output would have to be differnt for each engine speed...meaning accln WOULD be different.

 

[jiminy]

Nope...we've already established torque brings accln!

IF an engine produced 200bhp at 3000rpm AND 7000rpm....the torque output would have to be differnt for each engine speed...meaning accln WOULD be different.

is it not theoretically possible that this could happen?

so you are saying i was correct when i said gearing has a large effect on acceleration?

 

[stan*]

gearing massivley effects acceleration. A gerabox is simply a torque multiplier. it takes the torque from the engine and increases it by whatever ratio gear you are in (inc final drive). hence why u accelerate better in 2nd than 5th.