bernrex

I'm hearing 680 HP and 217-218 topspeed ... from an initial test of mule.

Is this rumor correct ?

Obviously topspeed of Devilray will be dependent on the final car's weight and Cd. If the reported HP is 680, and weight comes in at 2900 lbs ... and assuming the Cd is same as the C7Z ....

What would physics equation predict for the Devilcar's topspeed ?

LTC Z06

Yes you could but you would need more than Cd, you also need frontal area I believe.

Tom400CFI

Weight has very little to do w/top speed. It has a large effect on the RATE at which you get to top speed, but heavy or light, everything else being equal, (power and aero) two cars will get to the same top speed.

shopdog

Drag power = 0.5 * Q * Cd * A * V * (V+Vo)^2

Drag power, in kilowatts, is the amount of power required to push the car to the speed V. (For those stuck in the imperial world, 1 kW = 1.34 Hp.)

Q is air density, 1.202 kg/m^3

Cd is the drag coefficient, a number between 0 and 1 that is a function of shape and surface condition. For the current base C6 it is 0.28, Z06 is worse due to tacked on scoops and spoilers. (0.31 as I recall)

A is the frontal area of the car is square meters.

V is vehicle speed in kph

Vo is the component of wind velocity in kph along, or opposed to, the line of direction of the car. In other words, for the purposes of the equation above, head winds are a positive quantity, and tail winds are a negative quantity.

Runge_Kutta

I posted this a few months ago.

======================================== ============
Oh, someone said the SS will top out at about 235 mph. No way. The
power required to hold a given velocity is proportional to Cd*A*v^3.
The Z06 tops out at 198mph with, say 440 RWHP. If the SS puts 575hp
to the pavement then it's top speed can be estimated based on the Z06.

vSS = vZ06 * ( (575*CdA_Z06)/(440*CdA_SS) )^(1/3)

The SS will present a larger cross-sectional area to the flow than
the Z06 and will have a larger drag coefficient. I suspect that
Cd*A will increase at least 10% with the SS. So,

vSS = 198 * ( 575/(440*1.10) )^(1/3) = 209.7
======================================== ===============

OK, let's say that the SS puts 625hp to the ground. Then we're are
215.6mph.

bernrex

Great stuff R.K. .... then, it looks like the D.R. car will put perhaps 635 or so to the ground if its aeros are similar to the Z's.

Halltech's word to the street is .... it ran 217 on a Z06 frame last summer in tests.

itchynackers

Actually, top speed is independent of a car's weight. If its heavier, it just takes longer to get to that speed.

Racer X

Weight is not an independent variable in the equations, to say top speed is independent of weight is not entirely factual. The affect of weight is embedded in other variables. It can greatly affect rolling resistance. It can affect frontal area, as heavier cars tend to be physically larger. They can require wider tires to accomodate larger loads, which impacts frontal area.

If weight has no impact on top speed, do freight trains that have as much as 10,000 hp have top speeds that exceed 400mph? Of course not.

Weight may have minimal impact, but it does have some impact in the real world.

Al Pettee

Weight has an impact because it increases resistance to movement perpindicular to the force of gravity (downforce) which through friction from rubber contact to the road impedes this movement. If there were zero friction (resistance to horizontal movement perpindicular to gravitational forces), then weight would have no impact-compare to a puck on an air hockey table in which friction is minimal (but not zero) with air turned on, but greater with air off, slowing movement. A heavier puck would move more slowly versus a lighter puck with air turned off, but this difference would be minimized (although not negated) with air on.

Tom400CFI

You can offset added weigh and increased rolling resistance as a result....by adding air to the tires and getting the same net result (except slower acceleration).

The statement that added weight=great frontal area is ridiculous and has nothing to do w/this thread. Everything else being equal (meaning same car) weight will not have a notable effect on top speed.

Racer X

The friction of the tires on the road is impacted by the perpendicular force applied (weight). Increase weight, increase friction. Airing up the tires will not completely offset it.

If you reduce weight by reducing the thickness of the materials of the body panels, at some point the panels will begin to flex and impact the CD of the car. So weight changes can impact other variables.

The Blue Devil is the subject of this thread. Where do you believe the additional weight will come from. Do you doubt they will try to put wider wheels and tires on it? If they do, the car will have greater frontal area. Will they widen the fenders? If they do, they will increase the frontal area. You have missed my point, if you put lead in the car so that it does not change the roll centers, weight distribution, polar moments and adjust the springs so the ride height does not change, and god fixes the tires so the rolling resistance does not change, then maybe the top speed would not be affected materially. However, that is not how the weight will be added in the real world.

It is not that you have added weight, it is how you add the weight (except rolling resistance).

I am sorry that I did not describe my position in sufficient enough detail for you to understand, or that I did not make my explanation of the really complex interactions necessary to properly modify a production vehicle to a higher level of performance, and a different enough look to justify a 30-50% increase in price, simple enough for you to understand. I apologize for my lack of eloquence.

Most things in physics are simple in the theoretical world, however, the real world is much more complex. One can rarely hold all other things constant, in the real world.

You don't need to be insulting to disagree. If you don't understand a position, all you need to do is ask for an explanation. You don't need to call someone ('s statement) “ridiculous”. Once all sides have made their points clear, it will be clear to everyone, who, if anyone, is ridiculous, or ignorant, or misunderstood, or stupid. Name calling is not necessary.

Al Pettee

But you can't COMPLETELY offset it, even if the added air to the tires adjusts tire contact to equal that of a lighter weight car. ANY friction, no matter how small, produces a GREATER resistance to moving a mass the GREATER the mass of the object, even if all other variables of the two vehicles (Cd, frontal surface area, polar moment, etc.) are constant.

BTW, I'm a big Utah skiing and summer mountain climbing fanatic, so I imagine you must have a blast driving around those Wasatch canyon roads.

Tom400CFI

RacerX, you're right; I did come off too harsh, and it's is because I didn't consider all the factors you mentioned. Sorry for that.

Little and Big Cottonwood Canyons can be fun, but there is too much traffic, and too many hikers by the side of the road to really boogie. I've had a lot more fun driving the California coast.

32valves

my calculator says 218.6 (given equal aero to the Z06) so 217 sounds just about right.

2006c6keller

If tires didn't have any resistance, (friction and flexing from downward force - gravity) they wouldn't get warm or hot. They would be cold and that is not the real world. Just monitor the tire pressure sensors and note that the pressure is increasing from friction as you drive, even in cold weather. I'm not an engineer but I understand this. Did I oversimplify this?

Racer X

We are OK.

I am sometimes a non-linear thinker, and often a stream of conciousness writer, and often when online I do not go back and read what I write to edit for clarity. As a result, sometimes people don't get my point because they don't think like I do, or can't read my mind (and if they did think like me or could really read mt mind, the world would be a scarier place ).

The writer has primary responsibilty for ensuring his thoughts are clearly presented. I failed. Thanks for the time to allow me to clarify.

Gohard777

1st, the SS is not a mule yet, they did take the drivetrain and put it in a Z06, so they could have tested that. 2nd, the SS does not have more frontal area, I have seen them. and 3rd, it doesn't necessarily mean that GM will make the car in production that they have right now. Sometimes they make one car, and want to change it completely and the original becomes a concept car, happens all the time, and usually, I get to see 'them'.

Racer X

Interesting that you say the SS does not have more frontal area. That means one of 3 things; they have been able to reduce the frontal area (perhaps by lowering the roof or narrowing the track ), they made no body changes (disappointing); or they very coincidentally made changes to the body/tires that added frontal area in some places and reduced in other and changes exactly netted to zero difference in frontal area.

The z06 has greater frontal area than the standard coupe, large part due to the wider fenders. Did you mean to say that there are no significant or apparent differences in the frontal area?