Audi URS4 Speedweek

[urs4guy]

to put in into perspective:

my A4 theoretical top speed in 6th @7000rpm was 226mph, with 280?! bhp i could not pull more than 150ish in 6th but in 5th, on the rev limmiter was an indicated 160/165

closed road ofcoarse

Closed road huh? I'm trying to get my head around the math concerning your theoretical top speed of 226mph @ 7000rpm. How do you get there? Thanks for explaining to a poor island boy from Hilo.

Hap, wit dakine Hilo xplainin not from Evahboost, Maguire

[quattro84]

Closed road huh? I'm trying to get my head around the math concerning your theoretical top speed of 226mph @ 7000rpm. How do you get there? Thanks for explaining to a poor island boy from Hilo.

Hap, wit dakine Hilo xplainin not from Evahboost, Maguire

I get 185 mph @ 7000rpm with 6th gear ratio of RS4 box which is 0.684, diff ratio of 4.11, rolling circumference of tire just under 2 meters based on 17" wheels with 225/45 tires.

225mph would need 8500rpm.

[UrS4boy]

Oh yeah, he just went 250.009.

Just for fun:

Power needed to go a certain speed is said to increase with the cube of the velocity.

So the power needed to go 250 mph in a C4 is 227*(250/150)^3 = 1050 hp.

Sounds about right.

[quattro84]

Just for fun:

Power needed to go a certain speed is said to increase with the cube of the velocity.

So the power needed to go 250 mph in a C4 is 227*(250/150)^3 = 1050 hp.

Sounds about right.

That's the power needed to stay at that speed, so even more to accelerate to that point.
Rolling resistance due to friction & hysteresis in the tires needs to be added, as well as road inclination, and wind speed added or substracted to be precise.

[Error404]

I'm surprised he's not done more in terms of aero as that must make an immense difference above 200mph... or are you not allowed to due to the rules etc?

[A1QSHIP]

I'm surprised he's not done more in terms of aero as that must make an immense difference above 200mph... or are you not allowed to due to the rules etc?

When you run in the "stock" class at Bonneville you are limited to the changes you can make to the bodywork. This vehicle retains the stock exhaust system installed for smother airflow under the car in spite of a side exit pipe for that mahoosive turbo.

[UrS4boy]

That's the power needed to stay at that speed, so even more to accelerate to that point.

No.

[UrS4boy]

When you run in the "stock" class at Bonneville you are limited to the changes you can make to the bodywork. This vehicle retains the stock exhaust system installed for smother airflow under the car in spite of a side exit pipe for that mahoosive turbo.

Agree and to add to that, if you look at the hood/bonnet above the right headlight there is a piece of aluminum that is pop-rivited to the hood. That is because they tried to use a NACA duct (above the turbo inlet) to feed air to the turbo. Nope, that is a modification to the bodywork that is not allowed (but notice no exterior mirrors is okay).

[mouse]

The full interview from last year is a good read

http://www.quattroworld.com/speed-week/the-worlds-fastest-audi-242mph-audi-s4/

Talks about some Aerodynamics and aero related suspension settings too

[UrS4boy]

A lttle speed in gears info for comparison

This is for a stock car (7200 rpm rev limit)

[UrS4boy]

No. With Feeling.

That's the power needed to stay at that speed, so even more to accelerate to that point.

Sorry, I should have added this diagram that I drew years ago for another forum to my "No" post. Acceleration is provided by the horsepower that is being made that is excess of that needed to over come rolling resistance and drag, etc. Once the horsepower being made equals that forces of drag and rolling resistance, acceleration stops and terminal velocity is reached. One of the problems with this is as the speed increases, the engine RPM increases but at the same time horsepower starts to drop off (once past the point of peak hp).

[Kieron20V]

Pretty sure Sean is running on 2.5 v6 diesel box hence thd top speed.

[quattro84]

... Acceleration is provided by the horsepower that is being made that is excess of that needed to over come rolling resistance and drag, etc. Once the horsepower being made equals that forces of drag and rolling resistance, acceleration stops and terminal velocity is reached.

You are right sir, and i am aware of that.
What i ment to say was the same but you would need to add 0,.. hp to accelerate to reach that final asymptote of vmax. If there is no reserve power left, there is no energy to proceed to that speed right? All hypothetical...

I derived the basic laws to derive the drag coefficient of the S4 body to a CdA of 0,6119, based on Cd of 0,29 and drag area of 2,11m², what do you use?
Circumference of stock tires is just under 2 meters, like you use. Dynamically it would be a bit less because of deflection of tire side walls.

With stock gearbox it looks like you'd be hitting the vmax with stock 230hp at 272kph never finding the rev limiter at 7200rpm.

Guessed interpolated torque curve:


Speed curve for all gears: