It's a new exhaust so it's gonna smell a bit. The hiss is also normal when you put a set of HFCs on the vq37 vhr.

So I have read every post in this thread and now feel compelled to chime in.

In stock configuration you have two pre cats and two main cats. Now, you have a driver side unit and a passenger side unit. Each unit consists of 1 pre cat, 1 O2 sensor and 1 main cat. That O2 sensor is located directly between the pre cat and main cat. It is considered your rear O2 sensor. It is strictly for emissions and does nothing to your Air/Fuel ratios. Your front O2 sensors which are located in your exhaust manifolds control your Air/Fuel ratios. Most people commonly refer to the exhaust manifold as a header.

By going to an aftermarket catalytic converter you will eliminate your pre cats! If the anti fouler on your aftermarket cats are done correctly, you should not get a CEL. To also ensure you never get a CEL, you need to make sure there is no exhaust leaks. Specifically between the exhaust manifold and aftermarket cats.

If you hear a hiss under acceleration you most likely have an exhaust leak. It could be anywhere and what you are hearing is a fluttering sound. If you drive between to large objects, buildings walls, etc... it will be most prominent! The "hiss" under deceleration is completely normal. It is at it's loudest when most or all of the back pressure is relieved.

I think that about sums it up. If you have any questions, please do not hesitate to give me a call.

Thank you, Tony

Interesting, i didn't know they had extra cats on the 370, i'm assuming that the 350 still just has the two cats?

Thanks for the information! I was able to learn something from it.

It is the same on the 350 as well. I know that at first glance it can throw you off. But if you dissect it, you can see that the pre cat is metallic and the main cat is ceramic.

I was actually surprised to see something of that high quality in an OEM part. The bottom line though at the end of the day they are still too restrictive! You know as well as do I that aftermarket cats are well worth the money!

Thanks, Tony

Anytime! As an exhaust manufacturer and vendor, I want to help where I can!

Thanks, Tony

Why don't aftermarket / HFCs have a pre-cat, then?

Ahh, so if you remove the cat section on the 350z, it removes them both?
There's nothing in the manifold? and nothing in the Y pipe?

Because...

pre-cats, or "pup" catalytic converters are there to reduce emissions before the catalytic converters heat up. The down stream 02 sensors aren't heated up and working at this point, either, so it wont throw a CEL if they are missing, and noone (meaning not me) really gives a **** about preventing the tiny bit of pollution experienced before the main cats achieve light off, and eliminating them reduces restriction to flow.

That is correct.