Everyone here is on point. The engine braking will be exactly the same until your rpms drop "below engagement" which is essentially 1800 rpms. When you are decelerating that's usually around 5-6 mph. At that point the belt makes a transposition from the sheaves to the one way/two way bearing and That point if equipped with a one way bearing, that handled the engine braking. On aftermarket primaries the bearing is a smaller diameter to give you more bottom end and a lower starting gear ratio. This also comes with a trade off. Stock clutching has a 55 mm one way bearing while after market clutching all offers smaller (50 mm cv tech, 45 mm STM, 44 mm QSC). With a smaller one way bearing you have a smaller surface area for the belt to "grab" onto.
Now on to the secondary. We battled this for months and months. I did so much testing and R&D trying to make it perfect it was unreal. A few changes were made to the design of the STM secondary to make the engine braking below engagement better. We cut helixes down to keep the secondary from trying to open on down hill descents, we had a notch cut into the gen 2 helixes. Several members on here were a part of this process as well and were happy with the results. Several out in the WV mountains.
Like stated before. The engine braking on any aftermarket clutch setup will act the same down to engagement rpm. In my personal, non biased opinion, the performance trade off of an aftermarket secondary is well worth it. Better back shifting, faster up shifting, and extremely tunable. The stock secondary is not capable of back shifting under a load. The STM will. It get you to and keeps you in your peak hp range faster and longer. The stock secondary is extremely inefficient and it puts you at a huge advantage up against someone that does have an STM secondary. In all scenarios.
Sorry for the long winded response. All in all the upgrade to the secondary is well worth it. Truthfully an unbiased, personal opinion.
