Corvette ZR1 hits 233 mph: Fastest car built by the automaker

In reply to TravisTheHuman :

For starters, what calculator or equations are being used to determine theoretical top speed? Is the horsepower  being used the the physical force (at the wheels) required to overcome the weight and aero forces, or is it also accounting for assumed inefficiencies for engine power?

Also, I am not finding officially published drag coefficient numbers for any C8, let alone for the ZR1. The CdA on the first page appears to be for the C7 Corvette, and the pre-adjustment Cd at that. Chevy later bumped the official number to .34, not including the extra downforce aero package(s). Apparently the full downforce setup took 8mph off the Z06 and 10mph off the ZR1.

With a .34 Cd x 2.023m^2 frontal area, the C7 top speed was claimed at 194mph for the Z06 (3524lbs) and 212mph for the ZR1 (3560 lbs). What is the power required for each of those?

With full aero that apparently dropped to 186mph and 202mph respectively. Assuming the same area, what is the drag coefficient required for that?

Now the C8 apparently has a slightly higher frontal area at 2.075m^2, and the ZR1 should add a little to that, so may be 2.08M^2. Assuming an equivalent percentage theoretical vs actual hp difference as for the C7 Z06/ZR1 above, what's the drag coefficient for 233mph with an expected ~4000lb curb weight based on the 3670lb 'dry' weight? Is the theoretica drag coefficient reasonable considering the amounts of downforce over the C7's also being claimed for the car?

wspohn said:

GM finally got to where the Jaguar XJ220 was in 1992 (they used a 500 bhp twin turbo V6)

That car was $650,000 in 1992. That's equivalent to a $1.5M car nowadays. Not in any way comparable to a $180k car. 

In reply to dculberson :

correct and only 282 were made in a 2 year span. they made that many standard c8s this week already 

dculberson said:

wspohn said:

GM finally got to where the Jaguar XJ220 was in 1992 (they used a 500 bhp twin turbo V6)

That car was $650,000 in 1992. That's equivalent to a $1.5M car nowadays. Not in any way comparable to a $180k car. 

...and a bit shy of the 233 mph ZR1.

Driven5 said:

In reply to TravisTheHuman :

For starters, what calculator or equations are being used to determine theoretical top speed? Is the horsepower  being used the the physical force (at the wheels) required to overcome the weight and aero forces, or is it also accounting for assumed inefficiencies for engine power?

Also, I am not finding officially published drag coefficient numbers for any C8, let alone for the ZR1. The CdA on the first page appears to be for the C7 Corvette, and the pre-adjustment Cd at that. Chevy later bumped the official number to .34, not including the extra downforce aero package(s). Apparently the full downforce setup took 8mph off the Z06 and 10mph off the ZR1.

With a .34 Cd x 2.023m^2 frontal area, the C7 top speed was claimed at 194mph for the Z06 (3524lbs) and 212mph for the ZR1 (3560 lbs). What is the power required for each of those?

With full aero that apparently dropped to 186mph and 202mph respectively. Assuming the same area, what is the drag coefficient required for that?

Now the C8 apparently has a slightly higher frontal area at 2.075m^2, and the ZR1 should add a little to that, so may be 2.08M^2. Assuming an equivalent percentage theoretical vs actual hp difference as for the C7 Z06/ZR1 above, what's the drag coefficient for 233mph with an expected ~4000lb curb weight based on the 3670lb 'dry' weight? Is the theoretica drag coefficient reasonable considering the amounts of downforce over the C7's also being claimed for the car?

 

Power equation I used is 

Road Load Force = [ 1/2*(density)*(Cd)*(drag area)*(velocity^2)] + [(mass w/driver)*(rr coefficient)]
Road Load Power = RLF * velocity

With a .34 Cd x 2.023m^2 frontal area, the C7 top speed was claimed at 194mph for the Z06 (3524lbs) - 401whp required
212mph for the ZR1 (3560 lbs) - 515whp

I don't know that either of those cars are at peak power when they hit their top speed, but assuming they arent, the numbers might be in the ballpark.  If the Z06 is geared such that its making 501hp when it hits 194, with a 20% drivetrain loss, that works out.  For the ZR1 with a 20% loss, it would be making 643hp.

With full aero that apparently dropped to 186mph - roughly 0.39
and 202mph respectively - also roughly .39-.40  

**not factoring in gearing changes.  The increased drag will not require more power from the car, but the lower speed pushes it further down in the powerband where it makes less power.

So yeah, if we assume the drag coefficient is ~.4, it does make the numbers work.  233mph would be 807whp, or 1008 with that 20% loss.  Well in the ballpark.

FWIW, with the original numbers on page 1 (2.05 and .31), 233mph would be 628whp.

Thanks for entertaining my math :)


 

** for drag area I used frontal area for worst case scenario.  I'm not sure how frontal area numbers posted were calculated.  SAE drag area is height*width*.8 to account for mirrors and whatnot, but at >200mph I imagine those small drag area differences can have a huge impact.