Dynojets give a higher hp/tq reading because they don't take into account atmospheric influences and whatnot. Mustang dynos (not Ford Mustang) are more accurate in my book, but give lower numbers. Craig at ...CUE>> has a top-of-the-line Mustang dyno on order! It takes into account vehicle weight, outside temp, atmospheric pressure, elevation, etc etc. You can get a fairly accurate 1/4-mile time on his dyno. I believe it also has automated rollers (say for a fwd, the rear roller are turned at the same rate as the front to simulate real driving, to diagnose problems for instance).

Dynopacks hook onto the wheel hub and are generally used to regestering gains/losses, not giving an accuarte hp/tq reading.