I have heard SO MANY times that ram air is useless until speeds that will never be attained by a car. (i.e 600+mph) Well, these guys who develope a ramair system for the C5 asy otherwise, and here is the article. I don't think it will have as much impact on a GTP, but a N/A gt or se will see that impact.
http://www.vararam.com/reality_of_ram_air01.html
BC
http://www.vararam.com/reality_of_ram_air01.html
BC