[jeegunkim]

I've got a JB4 with a custom map 6 tune on E85 blend with a catless downpipe with the stock exhaust. Totally safe to run with the stock exhaust and it definitely improves the exhaust sound, it's what I would consider "OEM+." Definitely not as loud as getting an aftermarket axle/cat back though.

I was running the JB4 with the stock cat for a while and adding the catless downpipe really opened up the car, the spooling of the turbo is noticeably louder and I could definitely feel the power gain it gave. I'm sure it'll be a nice upgrade along with your JB+ but like what Mike said, you get the full benefits with a real tune.

What's also really funny is that I have yet to get a CEL from the catless downpipe so far. So weird.