Drag coefficient

[TheRedSlantnose]

Pretty much all modern sports cars nowadays have readily-available info on their drag coefficient, but finding the drag coefficient of a 930/Slant seems to be nearly impossible without actually having to calculate it. A search on Google turned up no useful info on this topic and very vague answers about the Slant indeed having improved aerodynamics due to having a decreased frontal area, which is already pretty self-explanatory.

I already know the 930 has more drag since the wider body increases the area, but yet that's decreased to some amount with the Slant, but exactly how much? The drag coefficient of a 930 Slant is a pretty big mystery to me, but maybe I'm just not looking in the right places. I estimate it to be somewhere between 0.3 and 0.4.

Does anyone know what the drag coefficient is for the 930 Slant?

Thanks,

[Tilikum Turbo]

A standard 911 of the 70's/80's had a Cd of around 0.39 to 0.41.

I would guesstimate a Slant would be around 0.35 to 0.37

Consider the Slant has the advantage over a 911 with the Frog-Eyes lopped off, but the rest of it has the increased surface area/frontal area of the 930.

[SAY - 642]

Just for comparison: According to history-of-cars.com

Ruf CTR "Yellow Bird" 1987-1989, Germany

aerodynamics: coefficient of drag (cd): 0.34 - drag area: 7.026 sq.ft.

[Noah930]

I don't think it will be as low as you hope. From word-of-mouth ('cause I'm not sure Porsche ever publicized it) I've heard a stock 930 had a cD of close to 0.50. So I'd guess a slantnose 930 would be better than that, but I'd be a little surprised if it was < 0.40.

Part of what made the Yellowbird more slippery are details like the shaved rain gutters (can't recall if it had flush glass) for a lower cD, and the narrow, non-turbo body (less frontal area). So I'm not sure if it's easily comparable to a slantnose 930 for bench racing.

[Highway-Star]

Here are a lot of Porsche -models drag-coefficients:
CW-Werte Porsche-Typen - Forum: Porsche Fahrzeugpflege von PFF.de

But one value for all 930 LOL

[TheRedSlantnose]

Originally Posted by Noah930

I don't think it will be as low as you hope. From word-of-mouth ('cause I'm not sure Porsche ever publicized it) I've heard a stock 930 had a cD of close to 0.50. So I'd guess a slantnose 930 would be better than that, but I'd be a little surprised if it was < 0.40.

Part of what made the Yellowbird more slippery are details like the shaved rain gutters (can't recall if it had flush glass) for a lower cD, and the narrow, non-turbo body (less frontal area). So I'm not sure if it's easily comparable to a slantnose 930 for bench racing.

I suspected it wasn't made official because as I mentioned, it was basically impossible to find online.

The 930's drag coefficient is close to 0.50? That's almost as worse as a Mustang's, and very unexpected. You would think a high-performance sports car built for speed like a Porsche would be aerodynamically efficient, especially since the 930 is a step up from the non-turbo 911's of that time, but I guess not.

[clutch-monkey]

Originally Posted by TheRedSlantnose

I suspected it wasn't made official because as I mentioned, it was basically impossible to find online.

The 930's drag coefficient is close to 0.50? That's almost as worse as a Mustang's, and very unexpected. You would think a high-performance sports car built for speed like a Porsche would be aerodynamically efficient, especially since the 930 is a step up from the non-turbo 911's of that time, but I guess not.

wide guards, upright windscreen, gutters.. what were you expecting from a 1970's car? lol

[Noah930]

OK, I still don 't know the right answer. Does anyone have Paul Frere's book on the 911 Turbo, or Karl Ludvigson's Excellence Was Expected? But I looked at Paul Frere's Porsche 911 Story and got these figures:

The 934 had a Cd of 0.44
The 935-76 was 0.435

The H-series Carrera (I took it to mean narrow body) with front air dam & rear spoiler was 0.414
The H-series Carrera without aero aids was 0.423

The use of American market impact bumpers raised the Cd from 0.40 to 0.42. While Frere was not very clear to which 911 variant he was referring, the context seems to suggest that it's the narrow body car, not the turbo body. Still, if that's the Cd of a narrow body car, the Cd of a turbo body must be worse.

The 964: 0.32
The 965: 0.35
The 993: 0.33
The 993tt: 0.34

Edit: another book I have, Randy Leffingwell's Porsche 911: Perfection by Design lists a 1983 Carrera with a Cd of 0.40.

[Noah930]

The 930's drag coefficient is close to 0.50? That's almost as worse as a Mustang's, and very unexpected. You would think a high-performance sports car built for speed like a Porsche would be aerodynamically efficient, especially since the 930 is a step up from the non-turbo 911's of that time, but I guess not.

I've heard tongue-in-cheek speculation that the reason why it's so hard to find an actual Cd figure for the 930 is because the number is so embarrassingly dreadful.

[rsnodgrass]

So strange that no coefficient of drag or front/rear lift data exists for the 930 Turbo, either with original whale tail or the revised tea tray style tail. Anyone else found some rare mention somewhere?

[Rawknees'Turbo]

Originally Posted by rsnodgrass

So strange that no coefficient of drag or front/rear lift data exists for the 930 Turbo, either with original whale tail or the revised tea tray style tail. Anyone else found some rare mention somewhere?

Here is a tail comparison chart published by Porsche, way back in the day - the tea tray is the most effective, by far, at reducing rear lift.

[panzerfaust]

Originally Posted by Highway-Star

Here are a lot of Porsche -models drag-coefficients:
CW-Werte Porsche-Typen - Forum: Porsche Fahrzeugpflege von PFF.de

But one value for all 930 LOL

Are those recent test in a rolling road tunnel? Perhaps these are more accurate then the test conducted 40 years ago the old stationary tunnels

Interesting that they listed the cd for 3.2 n the 930 as the same?

Wind tunnels are like dynos.... hard to compare apple to apples

[panzerfaust]

Originally Posted by Highway-Star

Here are a lot of Porsche -models drag-coefficients:
CW-Werte Porsche-Typen - Forum: Porsche Fahrzeugpflege von PFF.de

But one value for all 930 LOL

Originally Posted by Noah930

OK, I still don 't know the right answer. Does anyone have Paul Frere's book on the 911 Turbo, or Karl Ludvigson's Excellence Was Expected? But I looked at Paul Frere's Porsche 911 Story and got these figures:

The 934 had a Cd of 0.44
The 935-76 was 0.435

The H-series Carrera (I took it to mean narrow body) with front air dam & rear spoiler was 0.414
The H-series Carrera without aero aids was 0.423

The use of American market impact bumpers raised the Cd from 0.40 to 0.42. While Frere was not very clear to which 911 variant he was referring, the context seems to suggest that it's the narrow body car, not the turbo body. Still, if that's the Cd of a narrow body car, the Cd of a turbo body must be worse.

The 964: 0.32
The 965: 0.35
The 993: 0.33
The 993tt: 0.34

Edit: another book I have, Randy Leffingwell's Porsche 911: Perfection by Design lists a 1983 Carrera with a Cd of 0.40.

As you can see the minimal drag cd improvemenst with the 934 vs 935-76. What would be really interesting is the difference with the center of pressure. Going slopenose by having the pontoon fenders off as well as the larger verticle wing supports would drastically move the center of pressure rearwards for high sport stability