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Old 4th February 2010, 23:12   #1
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Default Help me out with 10-sec car calculations !!

Hi.

I had this idea to calculate how much power an average car would need to qualify as a 10-second car. But the thing is that my calculations say that a car has to produce 686HP or more to perform as a 10-sec car, which sounds ridiculous. Can anyone help me out ??

My calcs

Distance travelled=1/4mile=402m. Let's assume 400m for the sake of simplicity.

Using s=ut+1/2at^2, we get a(cceleration)=8m/s^2

Force=mass*acceleration=1600kg(Assumed to be the average mass of a car)*8m/s^2=12800N.

Work done=400m*12800N=5120000 J

Power=Work done/time taken=5120000/10=512000W=686HP

This is an idealised situation. Taking into account things like friction, drag force etc. etc. I think power required can easily cross 700HP or more.

Is this right ? I mean, does it really take 520KW to power a 10-second car ? That amount could power 100 average homes...
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Old 5th February 2010, 00:35   #2
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Too tired to even attempt looking at that math -- but here is a program (which was given to me by Shan2nu) that might help you.

Rename the extension from .doc to .zip and extract the file. Its a oldschool DOS program, but its quite cool.

Also PM Shan2nu to draw his attention to this thread - its his type of thing and i'm sure he'll have something of value to add.

cya
R
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File Type: doc CarTest.doc (481.9 KB, 413 views)
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Old 5th February 2010, 01:06   #3
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How much torque is this engine producing?

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Old 5th February 2010, 03:45   #4
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what about losses? and you also need to take into account the rpm-power curve.
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Old 5th February 2010, 11:13   #5
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definitely helped me refresh my high school science

On a serious note, I want to know the answer to your question. Theoretically what you asked makes sense.

I was unable to open the word doc posted by Rehaan :(
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Old 5th February 2010, 11:27   #6
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Quote:
Originally Posted by vasanthn21 View Post
definitely helped me refresh my high school science

On a serious note, I want to know the answer to your question. Theoretically what you asked makes sense.

I was unable to open the word doc posted by Rehaan :(
Dude, rename .doc to .zip, unzip the contents into a folder and click the exe and WOLAAAAA the DOS program comes up.If you can't see than press ALT+ENTER to maximize.
Rehaan, thanks for the program.Wonderful and Excellent to have it with you.
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Old 5th February 2010, 11:48   #7
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thanks shishir, works perfectly.
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Old 5th February 2010, 11:56   #8
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The world record for a 1/4 mile standing start pass is 4.428 secs by Tony Schumacher.

Schumacher also holds the top speed record for the quarter mile at 336.15 miles per hour (540.98 km/h).

I wonder what engine he has used for such figures ??
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Old 5th February 2010, 12:03   #9
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You're right! It does take a lot of power to make a ten second car.

For instance, the McLaren F1 with 627 Bhp and much less weight does the quarter mile in 11.6 seconds!

P.S. A ten second car is one that does the quarter mile in 10.99 seconds or less. Not necessarily 10.0 seconds as you've assumed.
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Old 5th February 2010, 12:18   #10
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Post 10 Sec street legal car

The British built and designed US$130,000 Ultima GTR road car.

The 720 horsepower 990 kilogram Ultima is built in small numbers, To cap it off, the car set a standing quarter time of 9.941 seconds on June 9 (with a terminal speed of 143mph), making it the fastest production road car over that distance too.

Driven to the 0-100-0 record by Ultima Director, Richard Marlow, the GTR hits 60mph in 2.6 secs, 100mph in 5.3 secs and then brakes to zero from 100mph in just 3.6 secs, which are all in themselves road car world record times.
The Ultima GTR720 used in the attempt was fully road legal, road tyred and equipped with a standard 5 speed G50 transmission and a standard production engine option from Ultima’s official OE engine suppliers American Speed. No traction control devices or ABS braking aids were used.

Source : Gizmag
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Old 5th February 2010, 12:28   #11
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Quote:
Originally Posted by anku94 View Post
I had this idea to calculate how much power an average car would need to qualify as a 10-second car.
Power=Work done/time taken=5120000/10=512000W=686HP
This is an idealised situation. Taking into account things like friction, drag force etc. etc. I think power required can easily cross 700HP or more.
Is this right ? I mean, does it really take 520KW to power a 10-second car ?
Hi Anku, yes the numbers are impressive As an example, the Bugatti Veyron which produces ~1000 BHP & weighs ~1.9 tons does the 1/4 mile in ~10.3 seconds. I remember the "old" 3-liter F1 cars, which weighed ~600 Kgs, doing the 1/4 mile in 7 to 8 seconds. While the calculations are basically correct, they do not take into account aero-drag which is quite considerable at higher speeds.

The calculations assume a fixed acceleration of 8 m/sec^2 (~0.82 Gs) all the way, usually it's much higher at the start & falls off as aero-drag picks up. For example, at a constant acceleration of 8 m/sec^2, your terminal velocity at the end of 10 seconds is something like 288 Kmph, but the Veyron's speed at the end of the 1/4 mile is "only" 230 Kmph.

To give you an idea of aero-drag, at a constant 230 Kmph the total drag on my car (a little Alto) is ~1382 N, of which only 73 N is rolling resistance. At 230 Kmph I would need ~116 BHP just to compensate aero-drag ! At 288 Kmph, the drag on my car jumps to 2000 N !?! Anyway, to get a more accurate estimate of your engine needs, you'll need ~ torque across RPM figures, gearbox & final drive ratios, frontal area, drag coefficient, & also weight of the car itself.

P.S. - The drag numbers for my car were calculated assuming a Cd of 0.32 & a frontal area of ~1.8 meter^2...

Last edited by im_srini : 5th February 2010 at 12:30.
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Old 5th February 2010, 13:28   #12
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Dear Anku.

You are right in your calculation i believe, most of the card who do it 10 sec or less are really really high powered & lot less in weight.
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Old 5th February 2010, 14:27   #13
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You dont need 686bhp to do a 10 sec run. A 450bhp Ariel Atom does it in 10.8secs. Had this Atom been an AWD, it would have been even quicker.



Its all about power to weight ratio, torque to weight ratio, gearing, aerodynamics, traction etc.

A 686bhp car weighing 1600kgs has a chance of a 10sec run only if its AWD and has a strong torque curve.

You put a 2.4ltr 686bhp F1 engine in a 1600kg car and it will not be under the 11 sec mark. But a 7ltr 686bhp engine in this same car will be able to do it.

Shan2nu

Last edited by Shan2nu : 5th February 2010 at 14:28.
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Old 5th February 2010, 15:22   #14
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Question

Quote:
Originally Posted by Shan2nu View Post

You put a 2.4ltr 686bhp F1 engine in a 1600kg car and it will not be under the 11 sec mark. But a 7ltr 686bhp engine in this same car will be able to do it.

Shan2nu
Can you explain your statement a little in detail. I mean

1. How does the bigger engine size is going to make a car faster with same power output?

2. Bigger engine should be more heavy, more weight less performance decreases, common physics..

3. Arent F1 engines 3ltr V10 ?
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Old 5th February 2010, 15:36   #15
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Quote:
1. How does the bigger engine size is going to make a car faster with same power output?
Thats bcoz a 686bhp 7ltr NA engine will produce way more torque than a 2.4ltr F1 engine. Accelelration doesn't always depend on power or power to weight ratio. Torque also plays a big role in it.

Quote:
2. Bigger engine should be more heavy, more weight less performance decreases, common physics..
Overall weight of both cars being 1600kgs (idealised situaton) as mentioned by the thread started.

Quote:
3. Arent F1 engines 3ltr V10 ?
They were, 3 years ago.


Tell me something. Based on theory if you were to race a 560bhp/ton car vs a 520bhp/ton car, which should ideally be quicker?

Shan2nu

Last edited by Shan2nu : 5th February 2010 at 15:50.
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