Dyno numbers are great for one thing: comparing before/afters on the same car with the same dyno while adding modifications or doing other tweaks to affect the tune of the engine. Trying to compare Car A/Dyno #1 numbers with Car B/Dyno #2 is almost meaningless. One of the tuner magazines did a great article on this a few years where they took the same vehicle to 7 different dynos on the same day. Not only did they get 7 different numbers, but the difference from hi to low was 54HP!!

Lap times and 1/4 mile ETs with trap speed are a much better indicator of real performance. Nobody ever lost a drag race only to respond "oh yeah, well my car pulled 12HP more than yours on a dyno, so there!" At least, nobody who's taken seriously.