Top Speed Runs in S2

[Rusty]

1997 S4 Saloon Cd 0.31 Frontal area 2.03m^2
1999 RS4 Avant Cd 0.34 Frontal area 2.04m^2
1993 S2 Coupe Cd 0.32

[s2avant]

Email on it's way. I've included the program for calculating speeds, rev drops etc.

IIRC Lucas is using a 0.60 6th gear. That gives a big drop into 6th for the stock S2 box (not as bad on the DSY box). I think he said that was where he was getting his flatspot but I think for the normal driver it would be that much of an issue. Depends on that final stretch at VMAX though. If you are on a limited distance then it would become an issue. You'd be dropping around 1900-2000rpm going into 6th which could put you right out of the power band.

Ben

[stiglet]

its not the Cd i'd be worried about. Enough Power will overcome that to a certain extent. Its the Lift Coefficient. Most cars will have a natural tendency to lift off the ground with speed. This is why the S2 feels unstable with more speed. I'm guessing your S4 has some downforce to cancel this out which is why it feels stable?

034 did this at Bonneville salt flats. They used a 90 i think, with a specially made front bumper and a few other modifications. I would imagine the coupe rear window would give a bit more lift at the back end? Should be good fun anywyaz....

Good luck.

[Rusty]

Hence why a front splitter and a rear diffuser are a good idea... Even a subtle rear spoiler might help although that increases drag.

[stiglet]

You would be suprised what a small vertical lip on the end of the spoiler could do, similiar to nascar. It might not increase drag too much but could give a lot more downforce.

[Fat Audi 80]

Some of this surprises me, as my S2 Coupe always feel rock solid at high speed. I have seen 150mph on a private test track and felt like it would sit there all day. Does this feeling change when you get to 165, 170 etc??

The rear spoiler on the coupe is designed to hold it down...

Cheers,

Steve.

P.S. I know you got the jump on the Lambo Doug, but you still destroyed it!

[stiglet]

The rear spoiler on the coupe is designed to hold it down...

Cheers,

Steve.

I would have my doubts about the standard rear spoiler at high speeds. It may not produce enough downforce to counteract the lift at 200mph (which on a coupe will be huge).

[Keeper of The Kitten]

I suspect the coupe rear window area presents a relatively "flatter" rear bodyline than a saloon body, but that depends on whether the air stays attached to the saloon rear window (it's not that steep). But an Avant would likely be flatter still - that aids in reducing lift.

At the front, for higher speeds, excluding air is a big deal - a splitter that practically touches down, even if it is barn door vertical, will improve aero efficiency - people have tried faux-streamlining (wedge shapes) and it makes very little difference. Same goes for taping panel gaps, they're not such a big deal - but smaller (or no) mirrors will improve things.

Definitely worth lowering to present less of the tyres to the airstream, combined with closing larger volumes of air off from going under the car with the splitter.

I think the main issue with counteracting lift is to try and keep a balance - a small gurney on the rear might help but I would be reluctant to do anything without proving it in a tunnel first, although empirical testing in the real world would give a feel for what's going on. Sadly tunnel time is not cheap but then, neither is wrecking a car at high speed.

People must remember that Cd changes with speed - the figures that manufacturers quote are practically meaningless advertising blurb, particularly when you get into the realms of pushing for Vmax.

If I was going to put a finger in the wind, I would start with lowering the car to present less projected area and to exclude some air from under the car, and manufacture a splitter that closes off more air from going under the car. Use smaller/no external mirrors (depending on whether there is a rule about road legality).

Closing off the air that would enter the engine bay would make a difference (as much as possible), if the car can run without overheating. Suspect that this is one that will only be much good if you switched to ice tank air-water intercooling!

Beyond that - discs over the wheels (fixed discs on inside and rotating on the outside) - wheels are the worst aero barb on most cars. Slightly skinny tyres if you're feeling brave...

[VladaS2]

I've made this in the past and used it a lot for calculation of Cd, hp/vmax, 402 times and gear speeds: http://www.prelovac.com/aero/CAR%20MAX%20CALC.xls

[stiglet]

I suspect the coupe rear window area presents a relatively "flatter" rear bodyline than a saloon body, but that depends on whether the air stays attached to the saloon rear window (it's not that steep). But an Avant would likely be flatter still - that aids in reducing lift.

At the front, for higher speeds, excluding air is a big deal - a splitter that practically touches down, even if it is barn door vertical, will improve aero efficiency - people have tried faux-streamlining (wedge shapes) and it makes very little difference. Same goes for taping panel gaps, they're not such a big deal - but smaller (or no) mirrors will improve things.

Definitely worth lowering to present less of the tyres to the airstream, combined with closing larger volumes of air off from going under the car with the splitter.

I think the main issue with counteracting lift is to try and keep a balance - a small gurney on the rear might help but I would be reluctant to do anything without proving it in a tunnel first, although empirical testing in the real world would give a feel for what's going on. Sadly tunnel time is not cheap but then, neither is wrecking a car at high speed.

People must remember that Cd changes with speed - the figures that manufacturers quote are practically meaningless advertising blurb, particularly when you get into the realms of pushing for Vmax.

If I was going to put a finger in the wind, I would start with lowering the car to present less projected area and to exclude some air from under the car, and manufacture a splitter that closes off more air from going under the car. Use smaller/no external mirrors (depending on whether there is a rule about road legality).

Closing off the air that would enter the engine bay would make a difference (as much as possible), if the car can run without overheating. Suspect that this is one that will only be much good if you switched to ice tank air-water intercooling!

Beyond that - discs over the wheels (fixed discs on inside and rotating on the outside) - wheels are the worst aero barb on most cars. Slightly skinny tyres if you're feeling brave...

Not sure about the rear window, i would have thought it would be borderline for seperation.

Can definately vouch for the effectiveness of a gurney. Did some wind tunnel testing at MIRA and proved it was a very easy way to reduce lift without increasing drag too much on most vehicles. Doesn't need to be very big at all. Good point about the balance though!

Would agree best start with front bumper, lower, discs on wheels (as long as you don't have brake ducts!) and loose the wing mirrors.

[Doug_RS2]

I ran the S4 with no number plate on and open to the FMIC - i would have thought over a certain speed opening in hte bumper would not have that big an effect as you are not getting 150mph worht of air and volume through the coolers? i din't have an untertray on but i do have small mirrors on hte car!

Before doing the run in the S4 i would not even have thought about doing a 200mph run in a s2 - but after that did so well....

[4WheelDrifter]

Some of this surprises me, as my S2 Coupe always feel rock solid at high speed. I have seen 150mph on a private test track and felt like it would sit there all day. Does this feeling change when you get to 165, 170 etc??

The rear spoiler on the coupe is designed to hold it down...

Cheers,

Steve.

P.S. I know you got the jump on the Lambo Doug, but you still destroyed it!

Steve, if you're talking about a speedo indicated 150, that's still 4th gear on a 3B IIRC. I found it was shorty after shifting into 5th that the car started to feel a little 'floaty', so probably at about 155 mph (GPS) and above.

This is intersting stuff about aerodynamics guys, I did feel like this was where the problem lies. From what I've heard the Avant is a better shape for V-max.

@ Ben I'll be interested in the calculator you have. IIRC I'd have to rev to ~7800rpm to break the 200 mark, not that I'd want to try TBH.

[Keeper of The Kitten]

If you've got mesh grills on at the front they tend to stop air getting in a bit, which is why the ducting on race cars (for radiators) doesn't have the mesh at the opening - it's usually just before the heat exchanger. So the remark you made, Doug, probably does have some bearing on that.

But I would still say that closing air out is more likely to improve things.

Stiglet that's good information, knowing that a gurney worked for you - as I said it's surely important to see what the overall effect is (although you need to be careful with stuff close to the ground in a fixed plane tunnel).

I think I'd be tempted to go with inner wheel discs (as well as outers) and remove all brake ducting if it is present, you only need to do one stop at the end of each straight pass after all.

It goes without saying that side windows and interior air vents should be closed, but you might find that venting the rear bodywork (eg openings somewhere near the tail lights into the boot and cabin area) to relieve air pressure could also provides benefits.

[Rusty]

IIRC I'd have to rev to ~7800rpm to break the 200 mark, not that I'd want to try TBH.

What do you mean Stu, you big girl

[quattronutter]

i reckon you would be best off getting the car as low and stiff as possible on coilovers with an rs2 front bumper, sits lower than the s2 bumper and must have been designed with aerodynamics in mind by porsche,would be a good start anyhow