Cat 6NZ max the jakes

When I worked for a guy who had some older cats, he would insist the Jake was good enough because I was able to kick the crap out of anyone on the pull....

So I would head down the smasher and deploy!

 

Not much you can do with a 6nz Jake brake wise, about the only way you will get more back pressure to get more boost is to run a compound setup similar to an acert or a smaller turbo or a smaller turbo A/R. Right now the 6nz I have makes up to 20psi of boost during braking with a 78mm Borg Warner with a 1.7A/R, if I did a compound setup with say a 66mm I could probably get it up to 25psi, if I want Jake braking similar to to an isx then would most likely need to run a single 68mm with a 1.3 or 1.4 A/R a stock Garrett or holset that size might not workout but a sx400 would work fairly well but on acceleration I'd probably be making only 35psi of boost so my 550 would feel more like a 475, but to answer your question you'd be best with a compound turbo setup, lower turbo A/R and a smaller secondary turbo, a stock c15 will never compare to an isx15 or x15 because they use vgt turbo's. And yes Cummins is the king of Jake brakes because the founder of Cummins invented the Jake brake