I would like to know which is the most accurate dyno , the dyno jet or the Mustang dyno. The reason I ask is most everyone agrees to stay around 450 rwhp with a s/c engine, if the dyno jet reads 450 but the Mustang dyno reads 425. The Mustang dyno always reads lower,so which one would you use to be safe.

 

Don't trust either one... too many variables. "X" number of rwhp is not a guarantee of engine health. You're better off making sure engine and tuning variables are conservative. For example, you can make the same rwhp numbers on two different boost levels. What do you think would be more "safe", assuming both made about 440-450rwhp:

1) 10 psi boost, 16*-18* timing, A/F = 11.5:1
2) 8 psi boost, 22*-25* timing, A/F = 12:1

Personally, I'd take #1 anyday. But that's just me.

 

From what I have read, either dyno is accurate (assuming its being maintained and sensors are calibrated regularly/properly). One compensates for losses that the other does not. Obviously comparing numbers between either is futile.

Don's comment is correct in that you need to be looking the A/F and timing variables. Too lean and your toy will be broken soon.