js59

Stat boy - please reconcile viper acr vs regular viper top speeds in comparison to cd.

What is your explanation of the 20 mph difference? Honestly?

I'm about ready to take back my comment about appearing to be a smart guy. If you follow the viper models over the years, it would be pretty obvious. You are either so pissed off about your Atari gauges and flimsy seats that it is clouding your judgment or you are just plain jealous of those that own a well rounded sports car.

jsiddall

Sorry, I have no good explanation, but I agree that something doesn't add up. With all the aero I would be surprised if the Cd is the same on the C7s as the C6 but who knows.

mirage2991

CD formula has velocity squared, so perhaps the two cars have a CD taken a different speed? I mean yeah it's airplane talk where we consider lower velocity to be something bellow 200mph but….just a guess...

3 Z06ZR1

When you add slicks to the ZR1. Fartpipes 10.32@ 135.35 IS the fastest 1/4 mile. Z06 is yet to come close!

qlawson

As I understand it, the 186 mph figure corresponds to the Z07 configuration, with the higher Cd (.37?).

An important factor here is induced drag. This is directly related to downforce.

Also, Cd varies with the speed of airflow, uniquely influenced by the body shape.

Here are some additional resources on the subject:
http://www.formula1-dictionary.net/drag.html
http://wright.nasa.gov/airplane/drageq.html

JoesC5

The 186 number is what I've read but not from a credible GM source. And, like you state, it is probably is for the Z07 package, if it is the actual top speed. But the stage 1 C7 Z06 has a .35 Cd and has nowhere near the 205 MPH top speed of the ZR1with it's .35 Cd or the C6 Z06 with it's .34 Cd and 145 less horsepower.

JoesC5

So, you think GM measures the Cd of it's products differently, just to confuse the people on this forum. The way I understand it, they measure the drag in the wind tunnel, and then based on the car's frontal area, they calculate the coefficient of drag.

Maybe they measure speed differently also...you think????? Maybe 186 MPH on a C7 is really the same as 205 MPH on a ZR1, but measured differently. Maybe they measured the C7 Z06 moving in reverse while they measured the ZR1 and the C6 Z06 moving forward?

Or maybe GM measured the mile with the C7 Z06 at 5642 feet while they the measured mile with the C6 Z06 or ZR1 at 5280 feet?

JoesC5

Okay,

I have you recorded as not having a clue what you are talking about.....yawn!!!!!!

JoesC5

I'm just using the info that GM has provided. GM said the Cd of the ZR1 was .35 and GM said the Cd of the C7 Z06 stage 1 is .35.

.35 Cd = .35 Cd, anyway you want to look at it.

The C6 Z06 has a Cd of .34 but when you add the more aggressive front splitter, the side skirts and the larger spoiler from the ZR1, it has less lift but also a higher Cd of .35.

qlawson

My theory is that induced drag is the primary contributor to the top speed differences.

In the absence of published measurements, and using the limited information available, I assume the following:

Down force: C7Z06(Z07) > C7Z06(all others) > 0 > C6 ZR1 > C6 Z06

The production of downforce generates induced drag.

JoesC5

Don't you also increase the Cd when you increase downforce? If you take a car, say a stage1 C7 Z06 with a Cd of .35 and then add a splitter, spoiler and side skirts that creates, say, 100 pounds additional downforce, you will increase the drag and thus the coefficient of drag to , say, .37.

Any increase in drag increases the coefficient of drag.

qlawson

That approach can be used, as demontrated in the NASA article I referenced earlier.

Cd0 is the coefficient of drag without induced drag.

Since downforce is a function of velocity, the above definition of Cd is dependent on velocity.

I believe GM's published Cd value is equivalent to the Cd0 in this scenario.

mrstage1

winner right here. Without sourcing the formulas for the naysayers(who probably would still refuse to believe) the obvious answer is that the CD quoted is accurate. However, it is also plain as day the C7 Z has higher induced drag numbers as speeds elevate. Aero aids, lots of times, have little to no effect at lower speeds and also minimal drag as there isnt enough airflow to cause them to "work" at say 60mph. Therefore we see no "data" since they are basically not there. Now crank up the speed, increasing air speed differential over said aero aids top and bottom surface and the drag climbs as the begin doing their job. The act of redirecting the air over the surface gets harder to do as we get faster and faster.

Example. Hold your hand out the window of your car palm out at say 45degree incline. Do this at 20mph. Pretty easy to do. Now do the same at 70mph. Much harder to do as the airflow resistance is higher. Try it at a buck fifty and your arm damn near gets dislocated as the wind try to rip it backward.. Same phenomenon the Z06 is displaying.

Btw: CD is measured and calculated at xx speed. Likely below the threshold on the C7 Z06 before the aero bits get ahold. CALCULATED CD all factors included, is likely damn high above 125. Love to see a coast down from 150 by a C6 ZR1 and C7 Z06 to test that theory. Bet the C7 slows dramatically faster on coast down.

JoesC5

I understand what you are saying, but I also see the aero aids used on the stage 1 C7 Z06 to be pretty much identical looking to the aero aids on the ZR1. But then I see drag inducing items on the C7, such as the rear quarter panel scoops and the restrictive ducting and radiators used to cool the transmission and differential where as the ZR1 uses the engine coolant to cool the transmission and differential. That engine coolant is kept cool by the front mounted radiator, which the C7 also has. Routing the air through those scoops and through the ducting and the radiators can't be as smooth as the air flowing across the rear fenders and hatch on the C6.

The base C7 apparently also has a reduced top speed compared to the base C6, yet doesn't have the aero aids used on the Z06. I believe the C7's basic design isn't as "slippery" as the C6 or the C5 and that basic design is passed on to the Z06. I can't prove this, but I believe they made compromises in the C7's aero in order to achieve the "look" they wanted on the C7, from the start, that wasn't done on the C6.

What I find interesting is the GT-R's aero and downforce. The GT-R Nismo has a .26 Cd. Nissan increased the size of the rear wing and made revisions to the front splitter and the rocker panels to increase the downforce by 220 pounds at 185 MPh(I think that was the speed). But they also increased the car's Cd by doing that, so they made the front fascia a little wider and then lengthened the rear fascia a little while increasing it's taper and they ended up with a .26 Cd and it's top speed stayed at 196 MPH with the same 600 HP. Mt point....they increased the car's downforce but maintained the same top speed, by keeping the cd the same at .26. Velocity squared applies to the GT-R the same as any other C7 Z06 or the C6 Z06/ZR1.

I'm not arguing that increasing the downforce on the stage 2 and the Z07 increased the Cd and thus lowers the top speed, as it does, but I'm having a problem accepting that the same .35 Cd that is found on the stage 1 C7 Z06 and the ZR1 results in a sizable difference in the two's top speeds as they both have the same frontal area nearly the same horsepower(the C7 Z06 has the horsepower advantage). Nine MPH is sizable. I'm also having problems understanding why a 505 HP car with a .34 cd is two MPH faster than a 650 HP car with a .35 Cd. I don't understand how a .01 increase in the Cd negates 145 horsepower.

JoesC5

Are you aware that if you stick your hand out the window of a C7 Z06, you have the exact same airflow resistance as if you stick your hand out at 45 degrees in a C6 ZR1, at any speed you choose. The additional drag would measure the same in a C7 Z06 as it would in a ZR1 and thus you would have a corresponding increase in both car's coefficient of drag.

Flyboy22

If they have the same power and the C7Z has a lower top speed, then it has more drag. Period. This is not debatable.

mrstage1

yep

bdevault01

If the production specs are -

C6 ZR1
0-60: 3.3 seconds
1/4 Mile: 11.2 seconds

C7 Z06
0-60: 2.95 seconds
1/4 mile: 10.95 seconds (11.2 for the manual)

Then why does this thread exists. It says right there that the Z06 is faster..?

thegame

Cause races are not run on paper

bdevault01

I guess my sarcastic undertone wasn't obvious...