Clutch discs

The 5135 discs have a higher Cf (Coefficient of friction - heat tolerance without slipping) than the 5191’s. The higher the Cf of the disc, the less pressure or counter is generally needed to lock up the clutch. The 5191 is less aggressive, it’s ability to slip is greater and thus would require a higher static/counter combination to achieve the same hold as 5135.
With the lower Cf comes a much wider window of adjustment than the 5135 - meaning it is usually easier to get down the track without being ‘perfect’ on the clutch. Thus the 5191 as standard disc in the billet clutch...

The 5135 is real aggressive and is good for one run and has to be deglazed. If it is not deglazed after one run it will lock up real fast on launch. The 5191 can go for sevearal runs with out deglazing.