Does anybody know what the CD rating is on the 928 S4. I have heard that is was .32 in stock form. Also how about the frontal area, anybody know that? I was told it is 20 ft Can someone verify this information?

Thanks

 

The S4 CD is .36 with the cooling flaps open, and .34 with them closed; not very aero at all.

.36 is the CD of a pickup truck, literally.

 

WOW,

Thats terrible!!

 

Have pick-up trucks become THAT good in the meantime? I'd like to see some proof of that... it would amaze me.

Remember that the 928 was designed in the early 70ies where aerodynamic testing on production automobiles was still in its infancy. The original 928 was something like 042; the S was 0385 or so.

 

Tim... in "porsche 928", by J. Austen, p.121, he gives it as:
Area (meter sq.)= 1.98 (or 21.28)
Drag coef. = 0.34 (prob'y flaps, windows, sun roof closed)


G'luck.

edit - p.s. for comparison, at about the same Reynolds #,
one of Ken's liftbars, crosswise to flow, 1.0
a sphere, 0.6
a hemisphere, dome facing flow, 0.38
some NACA airfoils, 0.2

 

OK some numbers but no pickup trucks .. note that frontal AREA is critical to the amount of dragPorsche 924
0.31 - 0.33
1.80 frontal area in meters
19.37 frontal in sq ft
0.56 - 0.59
6.00-6.39 frontal area X drag co-effcient in feet;

Porsche 944 Turbo
0.33 - 0.34
1.90
20.44
0.63 - 0.65
6.75-6.95 ;

Nissan 300 ZX
0.33 - 0.36
1.82
19.58
0.60 - 0.66
6.46-7.05;

Mazda 626 Coupe
0.34 - 0.36
1.88
20.23
0.64 - 0.68
6.88-7.28;


Honda CRX Coupe
0.35 - 0.37
1.72
18.50
0.60 - 0.64
6.48-6.85;

Audi Coupe GT 5E
0.36 - 0.37
1.83
19.69
0.66 - 0.68
7.09-7.28;

Mazda RX-7
0.36 - 0.39
1.69
18.18
0.61 - 0.66
6.55-7.09;

Toyota Celica Supra 2.8i
0.37 - 0.39
1.83
19.69
0.68 - 0.71
7.28-7.68;

VW Scirocco GTX
0.38 - 0.39
1.74
18.72
0.66 - 0.68
7.11-7.30;

Porsche 911 Carrera
0.38 - 0.39
1.78
19.15
0.68 - 0.69
7.28-7.47;

Honda Prelude
0.38 - 0.40
1.84
19.80
0.70 - 0.74
7.52-7.92;

Mitsu Starion Turbo
0.38 - 0.40
1.84
19.80
0.70 - 0.74
7.52-7.92;

Porsche 928 S
0.30 - 0.40
1.96
21.09
0.74 - 0.78
6.33-8.43;

Por 911 Carrera Cabrio
0.40 - 0.41
1.77
19.04
0.71 - 0.73
7.62-7.81;

Jaguar XJ-S
0.40 - 0.41
1.92
20.66
0.77 - 0.79
8.26-8.47;

 

IIRC In the comparison book one of the reviews (Road and Track?) said that 928s were actually more aerodynamic going backwards than forwards. Don't know if this is true or not.

 

Thanks Jim.

 

Tim:

Just reconfigure the car so you can drive it backwards, and you will be much better off drag-wise.

 

Tim you know with .."6.4L / 515 rwhp / 519 tq *Street Legal ORR " who cares about drag

 

Tim
So figure yours is slightly better since its lower with a better airdam....maybe .33 or so....with a frontal area of 21sq ft that puts it at about 6.93.....which really isn't all that bad? My guess is you'll "find" some more HP over the winter and easily break the 210mph record!

 

The 928 rear-end, as attractive as that big, juicy butt is, is one of the biggest problems in terms or aerodynamics.

Somebody should come up with a Peter Brock-designed Cobra Daytona Coupe-style rear bumper cover. Brock based this on the aerodynamic ideas of Wunibald Kamm, and is called the Kamm-tail or Kammback. It was reported to have improved top speed and fuel economy by 25% over the more rounded earlier rear.

http://www.secondstrike.com/Coupe/Brock.htm

This back-end style is also seen on the Ferrari Dino.

If you've seen a 928 with the rear cover off, you'd see there is an opportunity to do this. The underlying structure is recessed quite a bit under the cover.

 

frontal area of a truck will be more and that means the drag will be more too!

at the top speeds, its all about hp to drag ratio

mk

 

The lower end looks very good versus the others but why such a wide range? It sort of damages the credibility of the numbers. Why should mine be 0.3 versus yours at 0.4; apart from the fact that I led a blameless life?

Marton

 

The VW Golf (Rabbit) 928 experiment in Germany purported to have a higher
top speed than the 928. That was the widened Golf body with a 928 chassis wedged into it. The more aerodynamic Golf yielded higher top end speed.
Think it pi$$ed off lots of Merc/BMW/Porsche's to have this economy Golf come up on the Autobahn and give them a flash to pass high beam.

Ernest (NYC)
That'll be a cool car to have.
"But Ossifer. Everybody knows a Golf cannot go 140mph."