Maybe a little late for an answer but for anyone else reading this... The 904 was a '60s racecar which 4, 6 and 8 cylinder versions. I believe the thread starter must have meant to ask about the 914 which had either a 4 cylinder (/4) VW engine or a "proper" 6 cylinder Porsche one (/6). Anyway, since the 904 is a stunning looking racer (and very succesfull too in its days) heres a link
http://www.flat-6.net/view.php?model...=904&tab=oview