Which is quicker?

[Gregry254]

I have been following this thread on another forum and now that I know the answer it all becomes clear haha

I'll leave it a few days and see how many get the right answer

Brain teaser for the bored

Car A produces 95.2 bhp @ 2000 rpm
Car B produces 119.0 bhp @ 2500 rpm
Both have the same weight and gearing.


Which car will most likely be the fastest accelerating vehicle ?



petrol or diesel ???
immaterial but I'll say max torque occurs at 3000rpm.
That should alleviate any potholes and smart arse repostes

what speed ???
not fast enough to incur serious drag.

 

[mrcinquecento]

Good one

i'll say which ones quicker depends on the driver, as both are the same spec of same car.

 

[Stuart]

depends on the driver and the engine, you say all these figures where the peaks are but how would the engine perform otherwise? flat spots etc.??

i would prob go for the smaller one as the peaks are further apart thus being at relativly peak power for longer

 

[ycming]

WTF? Is that peak power? Why is it making that sort of power at 2500 ?

Ming

 

[Stuart]

WTF? Is that peak power? Why is it making that sort of power at 2500 ?

Ming

driveability

 

[ycming]

driveability

That be too low for any sort of driveability

 

[Venters]

Car A. :cheesy:

 

[Gregry254]

Ok a little clue, there is nothing hidden here. The answer can be worked out from the information given

Its a brain teaser more than finding things like flat spots

I will post the answer when I get to work in the morning.

 

[Stuart]

That be too low for any sort of driveability

maybe for drivability for you and i, but what about people who dont use the whole rev range?

 

[Venters]

Should have made this a poll. Not that it matters cos my mate Mathematics says I'm right anyway.:****:

 

[Gregry254]

righttttttt time for the answer . . . lets see if Venters Math is up to the challenge or if it was just a lucky guess

BHP is irrelevant to accelerration.
What you are interested in is the turning force applied to the wheel.
Torque basically.
The greater the turning torque the quicker the car accelerates.

My 1st red herring was to tell you what the BHP was.

The formula for converting from BHP to torque is..
Torque (pound foot) = BHP * 5252 / engine RPM

So,
Car A = 95.2 * 5252 / 2000 = 249.9952 lb ft Torque
Car B = 119.0 * 5252 / 2500 = 249.9952 lb ft Torque

Quite a few of you were clever enough to get this far
But then assumed that as the torque was the same the acceleration was the same.

Which was the 2nd red herring

I also stated the Maximum torque did not occur until 3000rpm in both vehicles.
So the torque would increase upto this point.

Car B is producing 250 lb ft @ 2500rpm.
Car A is already producing this amount of torque at only 2000 rpm.
So by the time Car A reaches 2500rpm it will be producing more than 250 lb ft of torque and hence must be accelerating quicker at the same RPM.

Now I understand cars just that little bit more . . . how about you? lol

 

[Stuart]

toldyou it was the smaller one that would be quickest

 

[Venters]

HAHA My maths was wrong. Misremembered the constant used 2525 instead of 5252. Lucky it was the constant so answer was the same anyway.

 

[Gregry254]

At least you had the right idea

 

[granite]

wouldn't the drag co-efficient of each vehicle have a bearing on this, plus also the rolling resistance of the vehicles, so it may not be as clear cut as you state?

 

[Venters]

No because the problem is written to make the assumption both cars are completely identical, except for the differences mentioned in the description of the problem.

 

[ycming]

No because the problem is written to make the assumption both cars are completely identical, except for the differences mentioned in the description of the problem.

Doesn't say both car has the same shape, only "Both have the same weight and gearing."

Ming

 

[clock34]

doesnt say anything about V-tek . lmfao. or turbo boost (probably doesnt matter though)

 

[ycming]

Aye true no mention of gear ratio either

 

[clock34]

surley the bhp/torque figures also wont go up in a perfect diagonal?