In this thread I will show the difference in vehicle weight between the Nismo and the base model Z due to downforce at 103 mph. Downforce is no different than physically adding weight to a vehicle, it's just achieved through aerodynamic means instead.

Using the downforce formula located here:
http://redline.wikispaces.com/air+resistance#

I have come up with the following:

Fd = v^2 * Cd * 0.5 * Da

where v is velocity, Cd is downforce coefficient, and Da is the density of air in kg*m^-3, as you can specify in the environment. The default is 1.2929 kg*m^-3 (which is the approximate air density near sea level).

This means that if we know the amount of downforce generated at a certain speed we can calculate the downforce coefficient, like this.

Cd = Fd * 2 / (v^2 * Da)

We already know from car and driver that the downforce on the Nismo is 55 pounds at 75 mph. So we need to convert these numbers to kilograms and kilometers per hour:

1 lbs. * .45359237 = kg
1 mph * 1.609344 = kph (look these up yourself)


Fd = 55 lbs. * .45359237 = 24.94758035 kg
v = 75 mph * 1.609344 = 120.7008 kph

Then we need to calculate the downforce coefficient for the Nismo in order to calculate the downforce at different speeds:

Cd = Fd * 2 / (v^2 * Da)

Cd = 24.94758035 * 2 / (120.7008^2 * 1.2929)
Cd = 49.8951607 / 18835.850406675456
Cd = .0027

Or, you can use the calculator if you want, it didn't work for me. But you'll still have to convert to metric.

Now that we have the downforce coefficient for the Nismo we can calculate the downforce at 103 mph, the trap speed recorded by car and driver like this:

v = 103 mph * 1.609344 = 165.762432 kph

So,

Fd = v^2 * Cd * 0.5 * Da

Fd = 165.762432^2 * .0027 * 0.5 * 1.2929
Fd = 27477.183862554624 * .0027 * 0.5 * 1.2929
Fd = 47.959 kg

47.959 / .45359237 = 105.65 lbs. downforce @ 103 mph


Now, just to be fair. The same information provided from car and driver stated that the base 350Z had 18 pounds of lift at 75. So that means at higher speeds it's going to be more lift. We can use these same formulas to calculate that as well. Lift would simply be a negative number rather than a positive number.

Fd = -18 lbs. * .45359237 = -8.16466266 kg
v = 75 mph * 1.609344 = 120.7008 kph

Then we need to calculate the downforce coefficient for the base 350Z in order to calculate the downforce at different speeds:

Cd = Fd * 2 / (v^2 * Da)

Cd = -8.16466266 * 2 / (120.7008^2 * 1.2929)
Cd = -16.32932532 / 18835.850406675456
Cd = -.0009

Now that we have the downforce coefficient for the base 350Z we can calculate the downforce at 103 mph:

v = 103 mph * 1.609344 = 165.762432 kph

So,

Fd = v^2 * Cd * 0.5 * Da

Fd = 165.762432^2 * -.0009 * 0.5 * 1.2929
Fd = 27477.183862554624 * -.0009 * 0.5 * 1.2929
Fd = -15.986 kg

-15.986 / .45359237 = -35.24 lbs. downforce @ 103 mph, or 35.24 lbs. of lift


Now the vehicle weights would be adjusted as follows:
Nismo Curb Weight = 3353 + 105.65 = 3458.65
Base Curb Weight = 3339 - 35.24 = 3303.76

That's 154.89 lbs. difference in vehicle weight at 103 mph. Basically like having another passenger (either a small guy or a big girl). Is that weight enough to affect the trap speed and ET of a 13 second car? You tell me.

 

too much math involved... im stoopid...

 

Corrected

 

golf clap...the Nismo aint designed fer da 1320 homeskillet. see if you can mathematically figure out how much having an open diff kills launch btw Nismo would win, more grip, LSD, better launch.

 

Very true much more grip.

 

Congratulations. You win the bench racer of the month award.

 

 

You people have been bench racing this subject for days. I read it all. He is the only person who has actually provided something to back up his claim other than talk. What has anyone else done? The whole lot of you are bench racers. pfft.

 

Just what I was thinkin

 

Why not put the vehicles in a real race instead of a race on paper.

 

oh, i agree

 

i would assume the nismo would be quicker, otherwise i believe there would be some pissed off people angry they paid the extra money..

either way, impressive math skills dude.. i dont understand a damn thing you wrote but i assume its some hard sh*t.. congrats

 

I'd be happy to race a stock Nismo if anyone in the area would meet me at Bradenton Motorsports. I never said I wouldn't. I'm even in a Touring, not a Base which evens things out more. But since some of you mentioned the LSD, then compare against an Enthusiast and subtract 7 lbs. There's no aerodynamic difference.

I'm not a bench racer. Just because someone believes something and posts some fact to back up that theory doesn't make them a bench racer. I've been to the track, and I'll be going to the track again. I posted this to back up my "theory". Take it as you will, I don't care.

Bring a stock Nismo to the track for me and we'll settle it in real-time. At least now you'll have an excuse if you lose.

 

... nevermind

 

Well I have timeslips to back up my car. I even weighed my car on the scale at the track. Its nowhere near what Nissan claims.

I have over 80+ timeslips of my 07.
He has 1,2 maybe 3 at most. And he bases his thoughts by his 1 run and other people's timeslips which he cannot duplicate yet.

 

Bleh, I don't even pay attention to bench racing. If someone actually goes through with this race, take a vid and post it up on youtube though! Or at least ppost out some timeslips with pictures. I would actually be curious to see how the two stack up against eachother.

 

that weight is enough to make a difference IF its really a passenger AND all other things equal. but since the difference starts at 0 and works up from there, spending the largest percentage of the race being low (downforce increases exponentially with speed) its not like having a passenger. then you add in the difference that helps the nismo (lsd, stiffer rear suspension, downforce helps you not spin second or third, etc) its gonna be an even race. i think we can all agree that a 150lb difference at 103 isnt nearly the difference it is if youre starting from 0

 

Where's the "it doesn't matter" option?

The minute difference in weight will not matter too much in real life. Theoretically, the Nismo should be slower, but only on paper. That is, (going back to physics 101) in a perfect and equal launch and run (driving wise) for both cars with exact same coefficient of friction from the road surface, with exact same climate conditions, with exact same track variables, assuming both cars put down equal amount of power/torque to the ground on both wheels, etc etc.. Yes, the Nismo would be slower due to the stiffer suspension (affects launch), more downforce (which translates to more "weight"), among other things.

There are way too many variables to fully determine (and pointless) which is faster when in reality, DA and driver skills matter more than everything else.

 

Cool post 2007-Z. I'm too lazy to check the details at the moment, but will take a closer look later. Although, much of this comes down to the driver regardless, so even if a race is setup, it won't necessarily settle things.

I have a Nismo and have done a few short highway pulls against a stock '07 Z and it was pretty much even.