Our customer Sean wanted to add some more mods to his Z.  He brought it to us with Stillen Gen 3 Intakes & Stillen Catback.  Before installing the Stillen UD Pulley & Berk HFCs we got a baseline of where the Z stood.  Shortly thereafter we went ahead and installed the new parts.

Stock Crank Pulley

Stillen UD Pulley

The Stillen pulley is lighter by almost 4 lbs.  Factory pulley weighs in at 4.72 lbs and the Stillen piece at .99 lbs.  Accessories get underdriven by 20%.  The way these free HP is by removing weight, the lighter it is the easier it is for the crank to turn and by driving the accessories slower you also free power.  Judging by the before and after its hard to tell how much difference the pulley made.  Having not dynoed only one mod at a time we won’t know.

Stillen Catback

Berk HFCs  (Lookout for the header to factory CAT bolts!)

However its probably a safe bet to say that the HFCs made more significant changes.  AFR dramatically changed from before and after.  No tuning was done on our end.

It was a nice gain of 7 whp to get it over 320.  Most HP gains were had above 4700+ RPMs and torque benefiting all the way through the curve.  Sean’s Z is a strong performer judging by other 370s we’ve had on the dyno.  Tuning his AFR should get him some more mid-range power.