The first 928 (early '70s) made a Cw 0.39 with the 1:5 model (911 was Cw 0.381) I found a list that ist quite interesting, and contains a lot of Cw vfalues. Its in German, but not hard to understand. An English translation is below.
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hier nun die von Markus (MG) aus dem Elfertreff zusammengstellte Liste:
Luftwiderstandsbeiwert (Cw) x Stirnfläche (A) m2 = Luftwiderstandsindex

356/1 Gmünd 1948 (offen, mit 2 Personen): 0,45 x 1,41 = 0,648
356/2 Gmünd Coupé und Cabrio 1948 bis 1950: 0,29 x 1,62 = 0,469
356 bis MJ 1952: 0,296 x 1,677 = 0.496
356 bis MJ 1955: 0,365 x 1,692 = 0,618
356 Speedster bis MJ 1958, Convertible D 1959: 0,377 x 1,640 = 0,618
356 A: 0,365 x 1,692 = 0,618
356 B: 0,398 x 1,611 = 0,641
356 B Roadster: 0,386 x 1,599 = 0,617
356 B 1600 GS Carrera GTL (Abarth): 0,389 x 1,495 = 0,581
356 C: 0,398 x 1,611 = 0,641


550 RS Spyder: ?

904 Carrera GTS: 0,383 x 1,401 = 0,536

914 1,7 (auch 914/6, 914/8, 914/8 SII) MJ 1970 bis MJ 1973: 0,38 x 1,60 = 0,608
914 2,0 MJ 1973 und 1974: 0,38 x 1,60 = 0,608
914 2.0 MJ 1975 und 1976: 0,377 x 1,60 = 0,603

924 (MJ 1976 bis 1979): 0,36 x 1,76 = 0,634
924 (ab MJ 1980): 0,33 x 1,79 = 0,591
924 Turbo (931): 0,34 x 1,79 = 0,609
924 Carrera GT (937): 0,34 x 1,82 = 0,619
924S (946): 0,33 x 1,81 = 0,597

944 (auch S) MJ 1982 bis 1989: 0,35 x 1,82 = 0,637
944 Turbo (951), (auch S2, Turbo S, 968 CS, 968 Turbo S): 0,33 x 1,89 = 0,624
944 S2 Cabrio MJ 1989 bis 1991 (auch S2 Cabrio, Turbo Cabrio, 968 Cabrio): 0,36 x 1,87 = 0,673

928 MJ 1978 bis 1982: 0,41 x 1,95 = 0,799
928 S MJ 1980 bis 1986: 0,38 x 1,95 = 0,741
928 S4 MJ 1987 bis 1991 (auch CS, GT): 0,34 x 1,98 = 0,673
928 GTS MJ 1992 bis 1995: 0,35 x 2,02 = 0,707

986 Boxster: 0,31 x 1,93 = 0,598
986 Boxster S MJ 2000 bis 2002: 0,32 x 1,93 = 0,617

987 Boxster: 0,29 x 1,96 = 0,57
987 Boxster S: 0,30 x 1,97 = 0,59
987 Cayman S: 0,29 x 1,98 = 0,57

955 Cayenne (V6) MJ 2004: 0,38 x 2,78 = 1,056
955 Cayenne S (und Turbo) MJ 2003 + 2004: 0,39 x 2,78 = 1,084

901 1964: 0,363 x 1,685 = 0,612

911 MJ 1965 bis 1967 alle Typen (auch Targa und S): 0,363 x 1,685 = 0,612
911 MJ '68 (alle Typen): Cw x A (m2) = 0,381 x 1,6853 = 0,642

912: enstprechen den Elfern der jeweiligen Modelljahre

911 MJ '69-'73 : Cw x A (m2) = 0,408 x 1,71 = 0,697
911 RS MJ 1973: 0,397 x 1,73 = 0,686
911 MJ 1974 bis MJ 1977 (auch S, Targa): 0,39 x 1,76 = 0,686
911 SC MJ 1978 bis MJ 1983 (auch Targa und Cabrio) und Carrera MJ 1974 bis MJ 1977: 0,40 x 1,77 = 0,708
911 Carrera 3,2 MJ 1984 bis MJ 1989: 0,39 x 1,77 = 0,690
911 Carrera 3,2 MJ 1984 bis MJ 1989 mit Front- und Heckspoiler (auch Clubsport):0,38 x 1,77 = 0,672
911 Turbo (930), (auch WTL, SC/RS, Turbo Flachbau): 0,39 x 1,86 = 0,725

959: 0,31 x 1,92 = 0,595

964 (auch RS, RS America, RS N/GT): Cw x A (m2) = 0,32 x 1,79 = 0,573
964 Turbo (994), (Frere): Cw x A (m2) = 0,35 x 1,88 = 0,658
964 Turbo (994), (auch WTL, Jubi) (Bongers): 0,36 x 1,89 = 0,680
964 Turbo S Leichtbau (994), (auch RS 3.8, Turbo 3.6, Turbo 3.6 Flachbau): 0,35 x 1,89 = 0,662

993 (auch RS): 0,33 x 1,86 = 0,614
993 RS Clubsport (mit Hechlügel 0° Anstellwinkel): 0,34 x 1,86 = 0,632
993 RS Clubsport (mit Hechlügel 9° Anstellwinkel): 0,36 x 1,86 = 0,669
993 GT 2: 0,34 x 2,04 = 0,684
993 turbo (auch 2S, 4S, Turbo Cabrio): Cw x A (m2) = 0,34 x 1,93 = 0,656

996: Cw x A (m2) = 0,30 x 1,94 = 0,582
996 4S: 0,30 x 2,00 = 0,60
996 GT 2: 0,34 x 1,96 = 0,666
996 GT 3 MJ 1999 bis 2001: 0,30 x 1,95 = 0,585
996 Turbo: 0,31 x 2.0 = 0,62

997: 0,28 x 2,00 = 0,56
997 Cabrio: 0,29
997S: 0,29 x 2,00 = 0,58
997S Cabrio: 0,29

980 Carrera GT: 0,396 x 1,94 = 0,768

Theo
1988 928s4 cherry red
The Netherlands
928s4.no-ip.info
============================================

I found a list by Markus (MG) from the list put together by the 911 meeting that is quite interesting and contains a lot of Cd values:
Air resistance factor (Cd) x Front surface (A) m2 = air resistance index

356/1 GMÜND 1948 (open with 2 persons): 0.45 x 1.41 = 0.648
356/2 GMÜND Coupé and Cabrio 1948 to 1950: 0.29 x 1.62 = 0.469
356 to MJ 1952: 0.296 x 1.677 = 0.496
356 to MJ 1955: 0.365 x 1.692 = 0.618
356 Speedster to MJ 1958. Convertible D 1959: 0.377 x 1.640 = 0.618
356 A: 0.365 x 1.692 = 0.618
356 B: 0.398 x 1.611 = 0.641
356 B roadster: 0.386 x 1.599 = 0.617
356 B 1600 GS Carrera GTL (Abarth): 0.389 x 1.495 = 0.581
356 C: 0.398 x 1.611 = 0.641

550 R-S Spyder: ?

904 Carrera GTS: 0.383 x 1.401 = 0.536

914.1.7 (also 914/6, 914/8, 914/8 SII) MJ 1970 to MJ 1973: 0.38 x 1.60 = 0.608
914.2.0 MJ 1973 and 1974: 0.38 x 1.60 = 0.608
914.2.0 MJ 1975 and 1976: 0.377 x 1.60 = 0.603

924 (MJ 1976 to 1979): 0.36 x 1.76 = 0.634
924 (starting from MJ 1980): 0.33 x 1.79 = 0.591
924 turbo (931): 0.34 x 1.79 = 0.609
924 Carrera GT (937): 0.34 x 1.82 = 0.619
924S (946): 0.33 x 1.81 = 0.597

944 (also S) MJ 1982 to 1989: 0.35 x 1.82 = 0.637
944 turbo (951) (also S2, turbo S, 968 CS, 968 turbo S): 0.33 x 1.89 = 0.624
944 S2 Cabrio MJ 1989 to 1991 (also S2 Cabrio, turbo Cabrio, 968 Cabrio): 0.36 x 1.87 = 0.673

928 MJ 1978 to 1982: 0.41 x 1.95 = 0.799
928 S MJ 1980 to 1986: 0.38 x 1.95 = 0.741
928 S4 MJ 1987 to 1991 (also CS. GT): 0.34 x 1.98 = 0.673
928 GTS MJ 1992 to 1995: 0.35 x 2.02 = 0.707

986 Boxster: 0.31 x 1.93 = 0.598
986 Boxster S MJ 2000 to 2002: 0.32 x 1.93 = 0.617

987 Boxster: 0.29 x 1.96 = 0.57
987 Boxster S: 0.30 x 1.97 = 0.59
987 Cayman S: 0.29 x 1.98 = 0.57

955 Cayenne (V6) MJ 2004: 0.38 x 2.78 = 1.056
955 Cayenne S (and turbo) MJ 2003 + 2004: 0.39 x 2.78 = 1.084

901 1964: 0.363 x 1.685 = 0.612

911 MJ 1965 to 1967 all types (also Targa and S): 0.363 x 1.685 = 0.612
911 MJ ' 68 (all types): CD x A (m2) = 0.381 x 1.6853 = 0.642

912: Similar to 911 of respective model years

911 MJ ' 69-'73: Cd x A (m2) = 0.408 x 1.71 = 0.697
911 RS MJ 1973: 0.397 x 1.73 = 0.686
911 MJ 1974 to MJ 1977 (also S. Targa): 0.39 x 1.76 = 0.686
911 SC MJ 1978 to MJ 1983 (also Targa and Cabrio) and Carrera MJ 1974 to MJ 1977: 0.40 x 1.77 = 0.708
911 Carrera 3.2 MJ 1984 to MJ 1989: 0.39 x 1.77 = 0.690
911 Carrera 3.2 MJ 1984 to MJ 1989 with front and tail spoiler (also Clubsport):0.38 x 1.77 = 0.672
911 turbo (930) (also WTL, SC/RS, turbo slant nose): 0.39 x 1.86 = 0.725

959: 0.31 x 1.92 = 0.595

964 (also R-S. R-S America, R-S N/GT): Cd x A (m2) = 0.32 x 1.79 = 0.573
964 turbo (994). (Frere): Cd x A (m2) = 0.35 x 1.88 = 0.658
964 turbo (994) (also WTL, Jubi) (Bongers): 0.36 x 1.89 = 0.680
964 turbo S lightweight construction (994) (also R-S 3.8. turbo 3.6, turbo 3.6 low rise building): 0.35 x 1.89 = 0.662

993 (also R-S): 0.33 x 1.86 = 0.614
993 R-S Clubsport (with rear wing 0 Angle of incidence): 0.34 x 1.86 = 0.632
993 R-S Clubsport (with rear wingl 9 Angle of incidence): 0.36 x 1.86 = 0.669
993 GT 2: 0.34 x 2.04 = 0.684
993 turbo (also 2S. 4S, turbo Cabrio): CD x A (m2) = 0.34 x 1.93 = 0.656

996: Cd x A (m2) = 0.30 x 1.94 = 0.582
996 4S: 0.30 x 2.00 = 0.60
996 GT 2: 0.34 x 1.96 = 0.666
996 GT 3 MJ 1999 to 2001: 0.30 x 1.95 = 0.585
996 turbo: 0.31 x 2.0 = 0.62

997: 0.28 x 2.00 = 0.56
997 Cabrio: 0.29
997S: 0.29 x 2.00 = 0.58
997S Cabrio: 0.29
980 Carrera GT: 0.396 x 1.94 = 0.768

Theo
1988 928S4 cherry red
The Netherlands