How fast?

[George]

Hi

THe reson I always thought of 700-800 HP in a high end car was because they all weighed in at 1300-1500kg.

Now that I wanna go a GT40, the crazy thing weighs 841kg with carbon fibre. 700-800HP in that would be a 8 second car... thats totaly mental.

However I wanted to know how is top speed effected?

Does weight have any barring on that or not?

if not that means I need 700-800 HP to hit 360-400km/h (say 240mph) irrelivant of weight, in that case a heavier car would be better as it would slow down from the STUPID acceleration it would have being that light but still keep its 400km/h thing..

Kinda get what im saying?

WOuld the GT40 with 600hp, (crazy acceleration being that light) also be a 400km/h (240-250mph) car because its lighter and thus weight has something to do with top end as it does with acceleration... just wondering.

 

[Jon Briggs]

Top speed is all to do with max engine RPM, gearing (including wheels and tyres), and max horse power.

Weight has more to do with how fast you get to that top speed.

 

[David in Durango]

Well, I've always classified cars as pedestrian, peppy, performance and brutal.
I went to the Texas Mile and saw a hat that said "Stupid Fast" on the back. wtf?

See Jon's post above, gears, aero and power determine top speed.

this is stupid fast (238mph in a mile):

‪Underground Racing Twin Turbo Gallardo Crashes At 200+MPH Texas Mile‬‏ - YouTube (a rumored 1800whp)

 

[Mark]

Why do you want to make the car carbon fiber? Have you talked to any of the builders yet? If I were you I would give RCR a call and see what they can do for you. Even with 600hp that would be like strapping a rocket on your back. I have read some articles that a GT40 with 550hp and comparable torque will do 0-60 in under 3 seconds and hit a top speed of over 215mph.

 

[DaveM]

And where are you going to be driving 240mph even in Australia? Note the thread elsewhere on this forum about the 1200hp SPF GT40. Totalled the car on the freeway only a few months after completion. These big balls ideas about top speed are ridiculous. If you want big balls excitement race your car in sanctioned events at one of your tracks like Philip Island or Eastern Creek. Weight is not as much a factor of top speed as aerodynamics. Note the Bugatti Veyron at 2030kg.

 

[Dalton Veitch]

For an average car (not a GT40 type of car), with average drag coefficient, then assuming the car has suitable gearing the rule of thumb for the top speed used to be 57 times the cube root of the brake HP over the frontal area. (Imperial units of sq. ft. and hp). Of course, with exotic cars and high speeds all sorts of other factors come into play such as lift, aerodynamic stability, small details greatly affecting airflow and drag, and so on. But you can see that for, say, twice the speed you need eight times the horsepower (cube root of eight being two), other factors being equal.

 

[Cliff Beer]

As has been said, weight tends to affect how fast a certain speed is achieved rather than the maximum velocity. However, there are secondary effects of less/more weight that can affect max velocity to some degree. For example, a heavy car will need less aerodynamic downforce to maintain a stable attitude over the surface (ie. not take off and fly...) and that equates into less form drag, and higher speed. A heavier car will tend to use higher spring rates, and thus compress less as speed and downforce increases - this makes the aero easier to manage and more easily optimized for speed.

I've been involved in a project to turn a stock 150 mph sports car into a (still relatively stock) 200mph rocket. It's no easy task. Frankly, it's much more difficult than most people realize. That last 20mph on the way to 200 is very, very difficult to achieve, and manage. The aero is tough, and the hp requirements go up dramatically. If you've gone 150 in a car and thought "that's pretty easy, how tough can another 50mph be?" Well, the answer is "very tough."

 

[George]

Id only ever even 'consider' doing 200mph at a race track such as eastern creek, bathurst, or whatever else we got in this country... where... I dont know what else there is.

I was more or less just wondering if the car 'could' do 400kmh with 600hp, geard correctly. N if so, would it accelerate fast still or would that pretty much be out the window?

Wanting a Big Block in the car to produce 600 ft/lbs torque... would top end be sacrificed cause bigblocks dont rev as high as SB, or would it just achieve the same goal differently due to the increase In torque

N how the hell do ppl total there cars on the road?

Did the wind do something, was it the bad road, or the dumb Idea to go that fast, hit a bad crack in the road, went spinning n at that speed, its finished.????

I mean if the road ur driving on is dead straight, no Cars anywhere... I dont see how u can just'ops' off the road and totaled.
O and just cause u got 600 or even 1:1 ratio of 900hp in a GT40, doesnt mean u have to USE It. Meaning u can still drive it like a 100hp comuter if u wanted to

To me its not all about 'what will be done with the car' but knowing 'this car is capable of' - perhaps just numbers on paper... Why would I buy a Koenigsegg that runs 850HP?

Definately not cause im gonna be using everything its got to its limit. Id buy it casue it is what it is and it looks good and in return it just doest what it does. In this case I love the look of the GT40 but I wanna know I got hypercar performance underneath so I at least feel as though I got a hypercar without the hypercar $$$.

 

[Keith]

N how the hell do ppl total there cars on the road?

Red mist + the failure of the nut on the steering wheel = crash & burn.

You really should consider buying that 1200 hp SPF MKII from Ebay and fix it up. With that kind of power and rear weight you will get to the scene of your accident really quick.

Oh, I forgot, it already did that once for a previous owner! :laugh:

 

[Mike Pass]

I have just picked up a very interesting bit of info from the June edition of Motor Sport magazine. In his column Nigel Roebuck writes about his times spent with the incomparable Frank Gardner and his many pithy utterances. Of particular interest to this thread is the following description from Frank about his time at Le Mans.

He describes Le Mans as "that unbiased, unprejudiced race run by the French'!

He goes on to say " I was seconded to drive the Holman-Moody car there, with John Whitmore - and that's still the quickest car down the Mulsanne Straight. We were timed at 259.4mph and you didn't shift your chewing gum too far, I can tell you, because there was light rain and a little bit of fog about..... We didn't have downforce in those days of course."

Wow. When men were men....

Cheers
Mike

 

[Cliff Beer]

Id only ever even 'consider' doing 200mph at a race track such as eastern creek, bathurst, or whatever else we got in this country... where... I dont know what else there is.

I was more or less just wondering if the car 'could' do 400kmh with 600hp, geard correctly. N if so, would it accelerate fast still or would that pretty much be out the window?

Wanting a Big Block in the car to produce 600 ft/lbs torque... would top end be sacrificed cause bigblocks dont rev as high as SB, or would it just achieve the same goal differently due to the increase In torque

N how the hell do ppl total there cars on the road?

Did the wind do something, was it the bad road, or the dumb Idea to go that fast, hit a bad crack in the road, went spinning n at that speed, its finished.????

I mean if the road ur driving on is dead straight, no Cars anywhere... I dont see how u can just'ops' off the road and totaled.
O and just cause u got 600 or even 1:1 ratio of 900hp in a GT40, doesnt mean u have to USE It. Meaning u can still drive it like a 100hp comuter if u wanted to

To me its not all about 'what will be done with the car' but knowing 'this car is capable of' - perhaps just numbers on paper... Why would I buy a Koenigsegg that runs 850HP?

Definately not cause im gonna be using everything its got to its limit. Id buy it casue it is what it is and it looks good and in return it just doest what it does. In this case I love the look of the GT40 but I wanna know I got hypercar performance underneath so I at least feel as though I got a hypercar without the hypercar $$$.

It's easy to go off the road when the car goes over a small dip or bump in the road, some air flow gets under the front end, front end lifts, and front wheels lose steerage. I happens in the blink of an eye, and all of a sudden you're in the ditch. Easiest thing in the world.