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2376 posts

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  Reply # 1873928 28-Sep-2017 06:01
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Coil:

 

WyleECoyoteNZ:

 

And in terms of getting to the top speed of a Chiron or Veyron, as other have said, there aren't many places to do it, but you can have bragging rights at events like Vmax200.

 

http://www.vmax200.com/

 

 

 


You sure? Maybe not in a veyron or chiron but i've seen and heard of some real speed down this stretch.

 

 

 

 

*Edited due to formatting kept goign south. 

 

 

I know a guy who hasn't had a licence (or his bike) for quite a long time for doing over 260km/h on that stretch of road.





I know a little more than nothing but not much...

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Trusted

  Reply # 1873931 28-Sep-2017 07:24
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That stretch has got nothing on country/open roads


 
 
 
 


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  Reply # 1873966 28-Sep-2017 09:31
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This was just released today and is quite relevant.

 




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  Reply # 1873968 28-Sep-2017 09:36
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See next post



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  Reply # 1873976 28-Sep-2017 09:53
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Djmixerdomo:

This was just released today and is quite relevant.



Thanks Djmixerdomo. I just now watch that video, after I just posted the previous post.

I think I got his points.

He said that electric motors are more efficient, but do require the same amount of cooling per HP.

This came down to temperature differentials.

Internal combustion engine generate more heat, but can run at a higher maximum temperature.

The outside air is much cooler compared to the ICE engine temperature: big differentials mean easier cooling.

Electric batteries and motors generate less heat, but run at a much lower maximum temperature.

So the outside air is closer to the maximum temperature: smaller differential means harder cooling.


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  Reply # 1874001 28-Sep-2017 11:04
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kingdragonfly:
frankv:

 

EVs have "on-board efficiency" of around 80% according to Wikipedia. I guess this means that 20% of the battery energy gets wasted as heat. So putting 3000hp out (is that measured at the wheels?) means that 750hp is waste heat.

 

Wikipedia says ICEs are at best 37% efficient, and typically 18-20%. Let's assume a Bugatti Veyron SS engine is 30% efficient when making 1200bhp. So it must spit out about 2400hp in heat (and noise).

 

So for a rough approximation I guess that an EV needs about 1/3 the cooling of an ICE car.

 



So in the YouTube video about the Bugatti, the author made the point that the aerodynamics for the Veyron was the same as a Cadillac SUV.

The reason was the Bugatti had 10 radiators, in various scoops.

Based on the various forces, he calculated it needed 1,800 HP (plus 3,000 HP of cooling)

So anyhow less cooling = less drag = less HP.

I don't know what the final HP figure would be, but I'll WAG it at 1,000 HP to reach the same performance with body with less air scoops.

 

My guesstimates were based on Wikipedia which says the Veyron produces 1200bhp. Probably 3000hp of waste heat is more likely than my guesstimate of 2400hp. And, yes, forcing air into ducts and through radiator cores will cause drag, and potentially lots of it.

 

There's no simple relationship between "heat extracted" and "drag induced". You can even use the hot air that has gone through the radiator to produce thrust (The Meredith effect). The P51 Mustang produces net thrust from its cooling system. If Bugatti is clever, there may be no net drag from the radiators at all.

 

But it's tricky; to have adequate cooling at low speeds, you need large scoops. At high speeds, you can get away with smaller scoops because the airspeed of the vehicle means you catch a greater mass of air for the same scoop area. A scoop that is too large will cause drag. High performance aircraft have variable geometry in their cooling systems to maximise cooling at slow speeds and minimize drag at high speeds. 

 

 


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  Reply # 1874041 28-Sep-2017 11:34
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frankv:

 

Wikipedia says ICEs are at best 37% efficient, and typically 18-20%. Let's assume a Bugatti Veyron SS engine is 30% efficient when making 1200bhp. So it must spit out about 2400hp in heat (and noise).

 

 

But a good chunk of that heat is simply dumped out the back with the exhaust gases.

 

In an EV performing to the extremes required to hit 500kmh you will generate that in the battery due to discharge, the conductors to the motor and the motor itself.  Presumably you will be inverting to AC and the inverter will get hot as well.

 

Could that all be managed in a production car and be a reliable safe system?  I have some doubts. 

 

In a pencil car that runs for a few minutes, clearly it is possible.

 

 

 

 





Mike



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  Reply # 1874235 28-Sep-2017 16:36
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The irony is that batteries and electric motors that normally run hot would be easier to cool.

Obviously it wouldn't be fun sitting on top of a bunch of red-hot batteries.

Someone calculated on specific internal combustion engines seem to be more efficient till 27 C ambient temperature, when it got less efficient

http://eprints.uthm.edu.my/7540/1/MOHAMAD_FUAD_BIN_ABDUL_AZIZ.pdf

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