I ran the bigger of the 2 years ago in my mustang. Very good cam for stock to "mildly" modded 5.0s. Mine had ported stock heads, demon 650 carb on an rpm air gap intake. This cam was alot faster than the E-303 & the X-303 by a bunch. Low & mid range power were much better. My car had 3.55 gears & went from 83 mph best to 87 mph & 8.32 to 7.72 in the 1/8th. The only negative with it was the lack of lope at idle. The X cam sounded really good, the 258 was barely noticeable. Ive been told that on a fuel injected motor it has a more noticeable lope.