Viper's 200+ Top Speed capability

[Toronto_ACR]

Viper\'s 200+ Top Speed capability

can someone please tell me why if the viper can easily make 800+ horsepower, it cannot go easily into the upper 220 mile per hour speed zone. I was reading an article of the Corvette sledgehammer from the late 80's. It had 860HP and it achieved 252 miler per hour. Now I know that drag has a lot to do with it. But the Ruf Porsche had only 550hp and it got to 220 miles per hour also. The Viper is not that bad aerodynamically is it. you cant tell me that a Porsche is more aerodynamic than a Viper. A few years ago mario Andretti tested the fastest in the world in a road and track article. Hennessy had more horsepower than the RUF Porsche but the RUF Porsche beat it. In fact Hennessy could barely reach 200 miles per hour(205 mph).

Thanks

 

[Prashant]

Re: Viper\'s 200+ Top Speed capability

The truth of it is that the Viper is a brick wall when it comes to high speed aerodynamics. the new one should be allot better at cheating the wind.

 

[Robert1994]

Re: Viper\'s 200+ Top Speed capability

Check out the "wind-cheating" methods employed buy the number ONE car in the C & D One Lap Challenge. One picture tells
one thousand words.........

 

[dmora]

Re: Viper\'s 200+ Top Speed capability

It also has a lot to do with gearing.

 

[Toronto_ACR]

Re: Viper\'s 200+ Top Speed capability

I know the Viper is not good aerodynamically. But how does a porsche with its body shape beat it in top speed with half the horsepower. No one can tell me that a Porsche is good aerodynamically. Does anyone have the drag number from all the sports cars including of course the Viper. I heard that the viper has a drag coefficient of .35

What is the coefficient of a Porsche and Ferrari.

 

[Toronto_ACR]

Re: Viper\'s 200+ Top Speed capability

So Allan does that mean if the Viper had very low gears like the corvette sledgehammer had that we would see the Viper up at 240 miles per hour.

Can someone please tell me the grag coefficient of the Vipe compared to other cars such as the Porsche

thanks

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Alan M 98 GTS NY:
lower Rear gears as said in the above post. As in most cases you do not see all the behind the scenes car setup info for the car in magazine shootout testing. Most people think it is showroom stock condition. The mag that had the corvette top speed at 227? Those were not the stock supplied rear gears from the showroom. What is more impressive hitting 195 mph in a mile or so or 250 mph in around 6 miles? Given the correct gears and a long space to get up to speed does not mean the average owner will realize those on the street with his stock car.

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[Toronto_ACR]

Re: Viper\'s 200+ Top Speed capability

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by John Hennessey / HMS:
Top speed is a function of cd, cda (frontal area), power and gearing. weight has very little to do with top speed. frontal area probably has the greatest impact, then cd, then power. for example, a stock bodied viper requires about 520 rw hp to attain a 200 mph top speed. a C5 coupe requires about 450 rw hp to attain 200. the differences being the frontal area and cd.


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[Toronto_ACR]

Re: Viper\'s 200+ Top Speed capability

Thanks John for clearing up some of my questions. But I am still a little confused John on some things in relation to top speed. John when you were on Road and Tracks Top Speed Test of 1998 your car ran 205 miles per hour. But you were pushing 600 plus horsepower. But a few years ago in Motor Trend magazine a stock GTS ran 192 miles per hour. That car had 200 horsepower less than your car. Are you saying that it takes another 200 horsepower to get another 10 miles per hour. Please try to clarify and unconfuse me

Thanks

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by John Hennessey / HMS:
Top speed is a function of cd, cda (frontal area), power and gearing. weight has very little to do with top speed. frontal area probably has the greatest impact, then cd, then power. for example, a stock bodied viper requires about 520 rw hp to attain a 200 mph top speed. a C5 coupe requires about 450 rw hp to attain 200. the differences being the frontal area and cd.


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[Toronto_ACR]

Re: Viper\'s 200+ Top Speed capability

John thanks for your reply. YES! I am a 2000 ACR owner. I also race my car even with the malfunctioning 5 point seat belts in the ACR. You didn't really give me a direct answer but that is OK.

Thanks anyway!

 

[phiebert]

Re: Viper\'s 200+ Top Speed capability

To answer your question. I think what John was saying was although your comment about 200 hp to do 10 mph isn't exactly right, the answer is at those high speeds the amount of horsepower required increases rapidly for each mile per hour faster.

If you look at John doing 205 mph in an Venom 600 (it probably wasn't quite 600 hp, maybe more like 550, not a shot at HMS at all!). Then a stock GTS did 192 mph and was probably closer to 450 HP than 400. So the difference in speed was 13 mph and the difference in HP was probably closer to 100 HP. Now if you take into account all the other factors, wind speed, tire set up, each cars CD (they won't have been exactly the same) and you will find that your answer is yes. Just as John pointed out that a Corvette can do 200 mph with 450 HP and a Viper needs 520, that's 70 HP different for the same speed. So it it not unusual to expect one car with 100 HP only goes 13 mph faster than another, especially if their CD is different.

Just my two cents.

 

[SteveBCloud9]

Re: Viper\'s 200+ Top Speed capability

John, have to admit, your nice to everyone, even if they talk trash about you.
http://vca1.viperclub.org/ubb/Forum14/HTML/005289.html

 

[Scott J]

Re: Viper\'s 200+ Top Speed capability

Having a top speed of 220 MPH is completely absurd. Yes, we are all car enthusiasts and I don't mean to dampen the discussion, but top speed figures just don't matter for practical purposes (unless we're talking about a speed limiter being set too low).

Dodge may improve the aerodynamics of the car, but I'll take the tradeoff of a better looking design versus higher top speed any day - especially when the top speed is already approaching 180. Bottom line: I like my odds against your common Porsche any day of the week! If Stuttgart wants to invest a ton of money in a top speed vehicle, let them. There are plenty of rocket/car contraptions designed for the sole purpose of attaining high land speeds.

 

[Toronto_ACR]

Re: Viper\'s 200+ Top Speed capability

Bigjim, thanks for your answer. But what if a car had a rear wing added for downforce such as the GTSr in the Le Mans series. The GTSr is only 2600Ibs, but it has a rear wing added that adds to the weight due to downforce at high speeds. But you have said that weight does not matter. So then how does the GTSr with 600+ horsepower travel over 220 miles per hour. Meanwhile hennesey's car went only 205 miles per hour with about the same horsepower. Thats assuming you are correct that weight does not matter which I think you are correct.

Thanks

 

[dmora]

Re: Viper\'s 200+ Top Speed capability

The important things to look at are gearing, coef of drag, and power. You can have the power to overcome the drag, but if you run out of gear....? So you have to do everything jsut right. This is why there are testing sessions, and things to work out and math to be done. Its not an easy thing. This si why cars dont make it to magazine reviews all the time.

Hennessey is not here to please those brand ****** (auto mags), he just likes making the viper go fast. PERIOD.

 

[Supercharged Vipermad]

Re: Viper\'s 200+ Top Speed capability

AT 220MPH THE BALLS DRAGGING ON THE GROUND SLOWS IT DOWN A LITTLE.

 

[Supercharged Vipermad]

Re: Viper\'s 200+ Top Speed capability

OK. This conversation is getting a little too NUTTY for me.
Ill go ****** somewhere else until I get a grip on things and stop BALLING my eyes out.

Lets not forget friction. Where N is the force of the surface acting on the tire: W is the weight of car, P is a force pushing (or pulling) the tire in the positive i direction, F is the force of friction exerted by tires surface. If the tire is in equilibrium (no friction)or F = P. Note that friction force always acts opposite to the direction of motion (or impending motion).
Now, let's consider impending motion -- the tire is just on the verge of moving to the forwars, the maximum friction force will be equal to

F = uN u is called the coefficient of friction.
The Coefficient of most tires is 1.0-4.0 then the impending force on the pavement at high speeds is greater as the car speeds up. Thus slowing the car down. But you need traction to go that fast. Kind of a catch 22 if you think about it.
I dont know. Im ********

 

[dmora]

Re: Viper\'s 200+ Top Speed capability

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Ted Bigham:
I agree.

but... In an airless, frictionless environment, you'd only need a fraction of a horsepower to go 1,000,000 miles an hour, if you had the time.

<HR></BLOCKQUOTE>


No you wont... the car would go no where if there were no friction from the wheels to the pavement.

 

[treynor]

Re: Viper\'s 200+ Top Speed capability

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>349739942 x 3400 lbs. = 1,189.115802 lbs. of rolling resistance @ 210mph<HR></BLOCKQUOTE>

This cannot be. 1 horsepower = 550 ft-lbs/sec. 1189 lbs of force x 308 fps (210 mph) / 550 = 665 HP (measured at the wheels). Rolling friction is obviously not consuming 665 RWHP at 210 MPH.

As long as I'm in kibitz mode:

1) The gearing on the Viper is suboptimal, which acts to limit top speed. Ideally you would be at your peak HP RPM right at top speed. With Viper gearing, 5th is too short and 6th is way too tall for any near-stock car.

2) Production-based race cars typically have much less frontal area than do street cars simply because they're lower. The GTS-Rs may look like normal Vipers, but they're quite a bit shorter, largely because of their dry-sump engine and relative lack of suspension travel. Absent a high-drag wing, this reduced frontal area allows them to go faster with a given level of HP.

3) Although the force of drag increases with the square of velocity, it's important to remember that power ~ force * distance/time, so the power required to attain a given speed goes up as the cube of that speed.

4) last but not least, these are all approximations. If you want more exact calculations, you have to begin working with fluid dynamics equations, which exceeds the scope of this post.

5) there is no point #5.

6) No corvettes

 

[Toronto_ACR]

Re: Viper\'s 200+ Top Speed capability

In summary Treynor

If the Viper had a little better gearing a stock viper could reach 200mph. Then again if 192 mph was accomplished already with no modifications on motor trend then a viper with headers and exhaust plus smooth tubes for breathing would bring the viper to 200mph on a good day alone. This I hope to attempt shortly. I will let everyone know

Thanks