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Thanks to Iker for starting the discussion; I just incorporated the RWHP data along with the 5-6 shift, and also ran a sensitivity analysis on the coefficient of drag and the frontal area. I used Iker's formula for Vmax as it's part of a well recognized textbook Vmax formula (the rest of the formula considers other parasitic losses).
Some notes; In my simulations the C8Z always attained top speed in 6th gear; the 5-6 shift was not a limitation, when I varied estimated shift points to hit 6th anywhere from 188 to 195mph.
In the top graph, where the lines intersect, is the Top Speed. The bottom graph shows the variation of this intersection as parameters are varied.
Also, this isn't necessarily an accurate prediction, this is just fun with math for now as it contains assumptions and error bands.
Of course, these equations assume the engine speed is at the horsepower peak, and that coincides with the top speed of the car. Based on the gear ratios published on another thread, that's not lining up with the speeds above. So the +/- 2 mph error band is way over optimistic.
However, let's keep working in it. Is there a horsepower curve published for the Z06 engine?
Of course, these equations assume the engine speed is at the horsepower peak, and that coincides with the top speed of the car. Based on the gear ratios published on another thread, that's not lining up with the speeds above. So the +/- 2 mph error band is way over optimistic.
However, let's keep working in it. Is there a horsepower curve published for the Z06 engine?
The equaion we are going to use to calculate top speed is :
vmax = ( 2 · P / (c · D · A) )1/3
P = power in watt
C = drag coefficient
A = frontal area
D = air density, sea level = 1.25 kg/m³
Let’s start with the C7 ZR1 top speed to see how accurate this equation is
P = power in watt on wheels = 660whp = 492000 watt
C = drag coefficient 0.40 (low wing version)
A = frontal area = 2.10 (based on Tadge comment in question and answer section)
D = air density, sea level = 1.25 kg/m³
vmax = ( 2 · 492000 / (0.40 · 1.25 · 2.15) )1/3
Vmax = 97.2 meter per second = 350 km/h = 215 mph
Official top speed = 212 mph in 2 direction
992 GT3
P = power in watt at wheels = 445 whp = 336000 watt
C = drag coefficient 0.36
A = frontal area = 2.08 (based on Porsche website)
D = air density, sea level = 1.25 kg/m³
vmax = ( 2 · 336000 / (0.36 · 1.25 · 2.08) )1/3
= 89 meter per second
= 320 kmh = 198 mph
Porsche official website climed 197 mph official top speed
—————————————————————-
Let’s apply this calculation to estimate the new Z06 top speed
Z07 version
P = power in watt at wheels = 590whp = 440000 watt (assuming 12% drivetrain loss)
C = drag coefficient 0.47 (6% improvement over C7ZR1 Cd 0.50)
A = frontal area = 2.25 (assumption based on narrower previous generation 2.15)
D = air density, sea level = 1.25 kg/m³
vmax = ( 2 · 440000 / (0.47 · 2.25 · 1.25) )1/3
= 87.3 meter per second
= 314 kmh = 194 mph
Non Z07 version should have Cd around 0.38
vmax = ( 2 · 440000 / (0.38 · 2.25 · 1.25) )1/3
= 93.7 meter per second
= 337 kmh = 208 mph
Z07 = 194 mph
Non Z07 = 208 mph
+\- 2 mph
Excellent method to extrapolate top speeds. I am just adding Coefficient of drags numbers referenced in SAE and Tadge as well as official verified speed for the base C8 (non Z51).
Basically coming to this more from an empirical/observation angle and bottom up instead of top down. .
Also the assumption here is that when it comes down to top speed the advertised or video documented numbers from all manufactures reference the most sleek and less down force impaired version of the car.
Thanks to Iker for starting the discussion; I just incorporated the RWHP data along with the 5-6 shift, and also ran a sensitivity analysis on the coefficient of drag and the frontal area. I used Iker's formula for Vmax as it's part of a well recognized textbook Vmax formula (the rest of the formula considers other parasitic losses).
Some notes; In my simulations the C8Z always attained top speed in 6th gear; the 5-6 shift was not a limitation, when I varied estimated shift points to hit 6th anywhere from 188 to 195mph.
In the top graph, where the lines intersect, is the Top Speed. The bottom graph shows the variation of this intersection as parameters are varied.
Also, this isn't necessarily an accurate prediction, this is just fun with math for now as it contains assumptions and error bands.
Thanks to Iker for starting the discussion; I just incorporated the RWHP data along with the 5-6 shift, and also ran a sensitivity analysis on the coefficient of drag and the frontal area. I used Iker's formula for Vmax as it's part of a well recognized textbook Vmax formula (the rest of the formula considers other parasitic losses).
Some notes; In my simulations the C8Z always attained top speed in 6th gear; the 5-6 shift was not a limitation, when I varied estimated shift points to hit 6th anywhere from 188 to 195mph.
In the top graph, where the lines intersect, is the Top Speed. The bottom graph shows the variation of this intersection as parameters are varied.
Also, this isn't necessarily an accurate prediction, this is just fun with math for now as it contains assumptions and error bands.
To add to your great work above in an attempt to narrow the error band by getting the assumptions closer to reality, the number for RWHP needs some minor tweaking. Using a percentage of FWHP as a means to estimate RWHP is incorrect as there are exponential and constant sources of HP also. Using percentage only ignores both of them and implies the linear source is the only component of HP loss.
A more accurate way is to take the HP loss of a similar drivetrain like the base C8/Z51/LT2 and use the total HP loss with a few minor considerations, basically treat it as a constant loss plus or minus. Going through the C8 Tech forum, I found a post from a tuner stating he sees an average of 442 RWHP from the Z51 cars giving us a loss of 53 HP. The higher RPM of the LT6 will give more loss to churn/windage but not by a lot as the dry sump does its job. Another area is the sweep rate of the Dyno, the typical is 250 RPM/second which causes losses due to overcoming rotational inertia losses. While approaching top speed, the “sweep rate” is approaching zero also which means we can back out the HP loss due to rotational inertia. It’s not a lot to begin with due to the FPC of the LT6 and no driveshaft so I would call the small decrease a wash with the small increase in churn/windage.
Can you run the graphs again using 53 HP loss for a maximum of 617 RWHP? It looks like it may come out close to the OP calculated 208 MPH.
Ready to rip, LT6 delivers remarkable 670 net (per SAE Standard J1349) horsepower at 8400 rpm. The redline is 8600 rpm, while the torque curve peaks with 460 lb-ft (623 Nm) at 6300 rpm. The super-short stroke minimizes the crank’s rotating inertia, expediting the rush to the redline. Though executive chief engineer Tadge Juechter insists Z06 is not a “numbers” car – its official GM-listed top speed is actually slightly slower than that of the conventional Stingray – he does tout a 2.6-second 0-60 mph time.
Edit: which means the cD/frontal area are magnitudes (non linear) above base C8.....?
Not necessarily, it appears from reading the article that Tadge was talking about the Z07 equipped Z06. There was an interview/reveal where a GM rep (can’t remember who) stated the regular Z06 will slot between the C7Z and C7ZR which puts it between 205 and 212…right where the above calculations show.
Ready to rip, LT6 delivers remarkable 670 net (per SAE Standard J1349) horsepower at 8400 rpm. The redline is 8600 rpm, while the torque curve peaks with 460 lb-ft (623 Nm) at 6300 rpm. The super-short stroke minimizes the crank’s rotating inertia, expediting the rush to the redline. Though executive chief engineer Tadge Juechter insists Z06 is not a “numbers” car – its official GM-listed top speed is actually slightly slower than that of the conventional Stingray – he does tout a 2.6-second 0-60 mph time.
Edit: which means the cD/frontal area are magnitudes (non linear) above base C8.....?
I think that article is assuming that the 186mph speed that is used to describe the cars downforce is the cars top speed. Back when that article was written there wasn't (and still isn't) and "GM-listed top speed." Sometime last year I remember a video where Tadge was asked about top speed and he simply said they didn't know the top speed yet. But I've watched so many random Z06 videos over the last 6 months that I can't remember which one it was.
Ready to rip, LT6 delivers remarkable 670 net (per SAE Standard J1349) horsepower at 8400 rpm. The redline is 8600 rpm, while the torque curve peaks with 460 lb-ft (623 Nm) at 6300 rpm. The super-short stroke minimizes the crank’s rotating inertia, expediting the rush to the redline. Though executive chief engineer Tadge Juechter insists Z06 is not a “numbers” car – its official GM-listed top speed is actually slightly slower than that of the conventional Stingray – he does tout a 2.6-second 0-60 mph time.
Edit: which means the cD/frontal area are magnitudes (non linear) above base C8.....?
5th at peak HP rpm is low 190s according to my estimated gearing, so that would match up for Z07 atleast.
A more accurate way is to take the HP loss of a similar drivetrain like the base C8/Z51/LT2 and use the total HP loss with a few minor considerations, basically treat it as a constant loss plus or minus. Going through the C8 Tech forum, I found a post from a tuner stating he sees an average of 442 RWHP from the Z51 cars giving us a loss of 53 HP. The higher RPM of the LT6 will give more loss to churn/windage but not by a lot as the dry sump does its job. Another area is the sweep rate of the Dyno, the typical is 250 RPM/second which causes losses due to overcoming rotational inertia losses. While approaching top speed, the “sweep rate” is approaching zero .......
Can you run the graphs again using 53 HP loss for a maximum of 617 RWHP? It looks like it may come out close to the OP calculated 208 MPH.
All good points, sweep rate makes a difference - the vacuum pump and isolated block bays in this engine are a step above previous Chevys as well. I think the 617hp would be an upper limit -
corrected a typo as well, frontal area in the graph was 2.2 and not 2.25. One takeaway here is that we're really sensitive to area and drag coeff when counting MPH's, small changes make large differences. If you move the 5-6 shift to the low-mid 190's to account for any error in tire diameter I may have, the top speed difference isn't dramatically different, there may be a MPH or so here.
Ready to rip, LT6 delivers remarkable 670 net (per SAE Standard J1349) horsepower at 8400 rpm. The redline is 8600 rpm, while the torque curve peaks with 460 lb-ft (623 Nm) at 6300 rpm. The super-short stroke minimizes the crank’s rotating inertia, expediting the rush to the redline. Though executive chief engineer Tadge Juechter insists Z06 is not a “numbers” car – its official GM-listed top speed is actually slightly slower than that of the conventional Stingray – he does tout a 2.6-second 0-60 mph time.
Edit: which means the cD/frontal area are magnitudes (non linear) above base C8.....?
You're quoting something that is proven invalid as stated by others. There is no top speed and the 186(300kph) was a downforce reference. Now you will get people incorrectly quoting your incorrectly quoted post linked to non factual information.... And this is how the Internet works🙄
Thanks to Iker for starting the discussion; I just incorporated the RWHP data along with the 5-6 shift, and also ran a sensitivity analysis on the coefficient of drag and the frontal area. I used Iker's formula for Vmax as it's part of a well recognized textbook Vmax formula (the rest of the formula considers other parasitic losses).
Some notes; In my simulations the C8Z always attained top speed in 6th gear; the 5-6 shift was not a limitation, when I varied estimated shift points to hit 6th anywhere from 188 to 195mph.
In the top graph, where the lines intersect, is the Top Speed. The bottom graph shows the variation of this intersection as parameters are varied.
Also, this isn't necessarily an accurate prediction, this is just fun with math for now as it contains assumptions and error bands.
It is clear how tiny change in the numbers lead to a big difference in the results. Sure accurate numbers are needed for better results.
Do you have any idea how can we calculate the acceleration time from 0-186 mph and 1/4 mile trap speed for the base car?
05-23-2022, 10:58 PM
Top speed.. let’s do some math
