Drag Coefficient

[m2speed]

I have an excel spreadsheet for calculating top speeds and gearing selections for a Miata. I would like to use it on my Boxster but on of the things I need is the drag coefficient. I really would like to know it for the stock Boxster with top up, top down and hard top. Also any mods know to low the coefficient like different front end and lowering the cars overall effect.
I would like to post the spreadsheet for others to use but this site wont except it as an attachment.

Jeff

[blue2000s]

I seem to remember that it's about .32 with the top up. It's probably about .45 top down. Since it's vastly dominated by form drag, it should be about the same cd for hard top as top up, maybe a tick or two lower.

Where are you finding frontal area? Where are you getting the torque curve?

[Jeph]

Most of the results I find online say the Boxster is .29. But the ranges I have seen go from .29 to .31 -and that's for both 986 and 987. None of these numbers indicate top, down, or hardtop used. I would assume that it'd be convertible top up.

I'd find it surprisingly high at .45 with the top down. I'd love to see some source to back that claim up.

On a partially related note, evidently the Hummer H2 has a coefficient drag of .57!

Right from the Porsche web-site for the 987.

0.30 for the manual
0.31 for the Tip

http://www.porsche.com/usa/models/boxster/boxster-s/featuresandspecs/?gtabindex=5

From the Porsche sales brochure for the 2005 and 2006 987:

0.29 for the Boxster
0.30 for the Boxster S

[blue2000s]

Originally Posted by Jeph

Most of the results I find online say the Boxster is .29. But the ranges I have seen go from .29 to .31 -and that's for both 986 and 987. None of these numbers indicate top, down, or hardtop used. I would assume that it'd be convertible top up.

I'd find it surprisingly high at .45 with the top down. I'd love to see some source to back that claim up.

On a partially related note, evidently the Hummer H2 has a coefficient drag of .57!

Convertibles are typically in the 0.40-0.45 range.

[m2speed]

From the specs I have on Miatas is that the coefficient is top down is .44; top up .38; and hard top is .34. I think the Boxster hard top should be probably around .04 better also.