Better car engine sounds

[slickx]

What i did is find some dyno runs on youtube that were good enough and converted the video to mp3 than wav and choped them and tried to loop them. i do not know if that is bad or not since the videos did not have "all rights reserved".
found this http://porschedealer.com/sports_exhaust/ and i dont know ether if the sounds are usable for free or not

So let me know if this is cheating or not.
The sounds needed are as follow
Ill think of what do we need to make the cars sound great in terms of sounds and how to arrange them to work.Thanx for feedback