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post #101 of 131 (permalink) Old 10-16-2007, 11:09 AM
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Trying to remember my physics lessons so many years ago...

Quote:
Originally Posted by Stephen View Post
You are correct, and our cars do not have a good CD. Regardless of the cd of our cars, there is one fatal flaw with my horsepower calculations based on what our cars weigh. That flaw is when you begin to talk about top speed. In order for our cars to have the same top speeds as cars such as the Porsche 997, then we really would need to have those kind of HP numbers. As far as I know (please correct me if I am wrong physics guys), the weight of a car really does not affect its top speed. The weight will affect the amount of time it takes a car to get to its top speed (in other words the acceleration), but it will not affect the top speed. The only way that you are going to increase the speed of a car is by changing its aerodynamics, changing its frontal surface area, changing its gearing, and finally, changing its horsepower.

Lets say that my 2,000 lb 220 hp Exige S has a top speed of 150 mph, and a 0-60 mph time of 4.5 seconds. If I reduce the weight of my car to 1,500 lbs, and I change absolutely nothing else (other than maybe the spring rates and tire pressure, so that it has exactly the same stance as it did before), then I would expect my top speed to still be 150 mph, but my 0 to 60 mph time should drop significantly to something like 3.5 seconds.

I did not bring up top speed because we don't live in Germany, so who really cares. Our cars will do about 150 mph, that is plenty for the U.S. as far as I am concerned.





Actually because of the hp deficit, which is calculated from torque; so you are right. But as I said above, our power to weight ratios allow us to have the performance of 300 hp + sports cars; but jut not the top speed. To achieve that, we would really need to up the hp.

Stephen
I'm no physics expert but based on the ???th law of Newton when the weight of a car is increased you will need more energy (read: more hp) to get to the same speed. So increasing hp will have an effect on top speed. With diminishing returns though, because at higher speeds you'll need a bigger increase in hp to increase the max mph with just one mph (because the increase in drag is bigger from 150->151 mph when compared to 100->101 mph).

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post #102 of 131 (permalink) Old 10-16-2007, 11:34 AM
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Quote:
Originally Posted by E.D. View Post
I'm no physics expert but based on the ???th law of Newton when the weight of a car is increased you will need more energy (read: more hp) to get to the same speed. So increasing hp will have an effect on top speed. With diminishing returns though, because at higher speeds you'll need a bigger increase in hp to increase the max mph with just one mph (because the increase in drag is bigger from 150->151 mph when compared to 100->101 mph).
I think his point was that as you go higher in top speed aerodynamic drag expotentially increases and causes large requirements in HP for small increases in comparison to the power to weight ratio to improve 0-60 times. Limiting factor at speed is not so much the car's weight but what kind of aerodynamic wall you will it be hitting and how much excess HP you have to overcome that.
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post #103 of 131 (permalink) Old 10-16-2007, 11:35 AM
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From my perspective as a sportbiker, all cars feel rigid and slow.
....guess its time for an s/c and an arqray...

i'll give you the information if you stop hitting me...
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post #104 of 131 (permalink) Old 10-16-2007, 12:13 PM
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Quote:
Originally Posted by Lotus F1 View Post
I think his point was that as you go higher in top speed aerodynamic drag expotentially increases and causes large requirements in HP for small increases in comparison to the power to weight ratio to improve 0-60 times. Limiting factor at speed is not so much the car's weight but what kind of aerodynamic wall you will it be hitting and how much excess HP you have to overcome that.
Indeed!

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post #105 of 131 (permalink) Old 10-16-2007, 01:00 PM
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that is part of the reason why more HP would be helpful..

I know you are saying 150mph top speed is enough.. but on many road courses (road atlanta) you can easily get to 160 or 170..

poconoo raceway most of the big engine cars are getting up to 160 in the straights easily.. that is where the exige S will falter.. would be nice to have that high power handy..
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post #106 of 131 (permalink) Old 10-16-2007, 01:16 PM
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Exige S with 0.434 Drag Coefficient Top speed 137 30-60 2.9s , 30-90 8s , 30-120 20.2s

Exige S with 0.300 Drag Coefficient Top speed 151 30-60 2.85s, 30-90 7.6s , 30-120 16.75s

Exige S with 0.434 DC , peak tq 158 Top speed 144 30-60 2.7s , 30-90 7.2s , 30-120 17.15s

I couldn't find the frontal area, so i used 20ft2

And just for fun

Exige S with 0.300 DC , peak tq 158 Top speed 158 30-60 2.65s , 30-90 6.9s , 30-120 14.8s

Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!
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post #107 of 131 (permalink) Old 10-16-2007, 04:01 PM
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Quote:
Originally Posted by charliex View Post
Exige S with 0.434 Drag Coefficient Top speed 137 30-60 2.9s , 30-90 8s , 30-120 20.2s

Exige S with 0.300 Drag Coefficient Top speed 151 30-60 2.85s, 30-90 7.6s , 30-120 16.75s

Exige S with 0.434 DC , peak tq 158 Top speed 144 30-60 2.7s , 30-90 7.2s , 30-120 17.15s

I couldn't find the frontal area, so i used 20ft2

And just for fun

Exige S with 0.300 DC , peak tq 158 Top speed 158 30-60 2.65s , 30-90 6.9s , 30-120 14.8s
That all makes sense to me, but even though HP is a function of TQ, you still need to measure HP to determine the change in top speed, correct? Can't you technically increase torque, but not increase HP? What if we put a diesel engine in our cars that makes 260 peak TQ, but only 170 HP???

Also, what happens to your above calculations when you start to change the weight of the Exige S around; let's say in a range from 1500 lbs to 2500 lbs?

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post #108 of 131 (permalink) Old 10-16-2007, 04:05 PM
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at 1500lbs
Exige S with 0.434 Drag Coefficient Top speed 138 30-60 2.2s , 30-90 6.15s , 30-120 16.05s

at 2500lbs
Exige S with 0.434 Drag Coefficient Top speed 138 30-60 3.5s , 30-90 9.5s , 30-120 24.05s

none of the calcs i do use HP numbers, since torque is whats used to derive HP.

Also, does anyone know the actual frontal area of the exige/elise in ft ?

Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!

Last edited by charliex; 10-16-2007 at 04:13 PM.
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post #109 of 131 (permalink) Old 10-16-2007, 06:43 PM
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Quote:
Originally Posted by charliex View Post
Also, does anyone know the actual frontal area of the exige/elise in ft ?
According to:
http://www.sandsmuseum.com/cars/elis...ion/misc/nick/
the frontal area is 1.6m.
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post #110 of 131 (permalink) Old 10-17-2007, 08:54 AM
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cool thanks!

revised figures

Exige S
0.434 Drag Coefficient Top speed 147 30-60 2.95s , 30-90 7.85s , 30-120 18.45s
0.300 Drag Coefficient Top speed 167 30-60 2.9s, 30-90 7.55s , 30-120 16.1s
1500lbs with 0.434 Drag Coefficient Top speed 147 30-60 2.2s , 30-90 6.05s , 30-120 14.45s
2500lbs with 0.434 Drag Coefficient Top speed 147 30-60 3.45s , 30-90 9.3s , 30-120 21.65s

Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!

Last edited by charliex; 10-17-2007 at 09:34 AM.
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post #111 of 131 (permalink) Old 10-17-2007, 10:32 AM
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Quote:
Originally Posted by charliex View Post
cool thanks!

revised figures

Exige S
0.434 Drag Coefficient Top speed 147 30-60 2.95s , 30-90 7.85s , 30-120 18.45s
0.300 Drag Coefficient Top speed 167 30-60 2.9s, 30-90 7.55s , 30-120 16.1s
1500lbs with 0.434 Drag Coefficient Top speed 147 30-60 2.2s , 30-90 6.05s , 30-120 14.45s
2500lbs with 0.434 Drag Coefficient Top speed 147 30-60 3.45s , 30-90 9.3s , 30-120 21.65s
That is correct since the top speed claimed by the factory on the Exige S is 147 or 148 from what I remember.

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post #112 of 131 (permalink) Old 10-17-2007, 10:49 AM
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Quote:
Originally Posted by charliex View Post
cool thanks!

revised figures

Exige S
0.434 Drag Coefficient Top speed 147 30-60 2.95s , 30-90 7.85s , 30-120 18.45s
0.300 Drag Coefficient Top speed 167 30-60 2.9s, 30-90 7.55s , 30-120 16.1s
1500lbs with 0.434 Drag Coefficient Top speed 147 30-60 2.2s , 30-90 6.05s , 30-120 14.45s
2500lbs with 0.434 Drag Coefficient Top speed 147 30-60 3.45s , 30-90 9.3s , 30-120 21.65s
So not taking the wife along means that 0.1 sec faster from 30-60, 0.3 sec faster from 30-90 and 0.7 sec from 30 -120 then?

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post #113 of 131 (permalink) Old 10-17-2007, 10:52 AM
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yeah switching from 20ft² to 18ft² made a big difference, i'm adding in more dyno points now which should make it even more accurate, currently i'm using 2000-8500 rpm in 500 RPM increments which is a bit rough, and the lotus 2057lbs weight claim.


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Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!
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post #114 of 131 (permalink) Old 10-17-2007, 11:57 AM
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charliex

Can you please do the numbers on a stock 06 elise and a sector111 SC please.
what are the acceleration and top speed numbers to be expected?

thanks!!
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post #115 of 131 (permalink) Old 10-17-2007, 12:26 PM
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Standard Elise S2

Using 1975lbs with a DC of 0.36 ( I don't know if this is right, i have 0.434 for the exige )
Top speed 145 (137 with 0.434 ) 30-60 3.45s, 30-90 9.15s, 30-120 21.05s

I have to add in the dyno torque figures for the katana, so i'll post the results in a bit.

Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!
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post #116 of 131 (permalink) Old 10-17-2007, 12:34 PM
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Katana SC
2000lbs ( i guessed 25lbs for the SC ) 0.36DC
Top Speed 159MPH, 30-60 2.85s, 30-90 7.4s, 30-120 16.35

I have to go over and double check both sets, since i just did the dyno sheet import, but it looks close.

Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!
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post #117 of 131 (permalink) Old 10-17-2007, 05:33 PM
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High horsepower guys need to get the Toyo larger 6th gear for the increased top end
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post #118 of 131 (permalink) Old 10-17-2007, 05:59 PM
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I don't know jack-diddly about physics, but I do know that while I might walk away from Corvettes and M3s in the corners, they catch back up on the straights. And if a horsepower car is on my tail out of a corner, and then we're side by side in a drag race to the next corner, he suddenly starts pulling away at about 80-85mph. So, yeah, there is a reason why the platform should have more power. (I don't autocross; only track.)

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post #119 of 131 (permalink) Old 10-17-2007, 08:02 PM
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I was reading about S1 elise & exige...Says the exige has the SAME Cd as elise. How the hell did they do that with S1, but not with S2?

** save ~10 lbs gain 1 hp ** EQ: Y=(190*X) / (1984-X) where Y is (HP) and X is (lbs)

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post #120 of 131 (permalink) Old 10-17-2007, 08:10 PM
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S1's are just awesome, and the S1 exige even more so, thats all there is too it

Black Exige S / Elan M100. Don't run a smaller pulley without an upgraded fuel pump! http://www.goth.am ecu stuff.. New reflash box coming soon!
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