Exhaust diameter
 

So I have searched for awhile now and can’t find an answer. Wanted to see if anyone could help.

I have had beluga test pipes on for about 4 months now, and I’m getting tired of the fumes. So I decided to get HFCs, but noticed the z1’s are 2.5” outlet. I know my catback exhaust has a 2.25” diameter and I started thinking maybe I’m having more fumes or a leak because my test pipes are also 2.5” and found out they were.

So my question is, is it bad to hookup a 2.25” catback to a 2.5” hfc/tp? Does it cause any problems at all?

The stock exhaust is 2.25, not sure about the stock cat. If the exhaust smell is present in the cabin i would for sure check for leaks.

To answer your question check that video, i think he put it in a way better way than i could explain it
https://youtu.be/jjPeP_Nn2B4
-FJ

Thanks. I understand the importance of exhaust velocity and all that good stuff. I’m just asking if bolting a 2.5” outlet cat to a 2.25” y-pipe is bad.

The only time you should smell fumes is standing outside at the back of your car. I have test pipes and the only time I smelled them were during the initial period.

To your question, "bad", not in the sense your going to harm your car or see a noticeable change in power. But it's not good either.

Yea maybe I have a leak at the manifold or something, but I doubt it. Other members say they’ve had similar exp when they’re running their climate control but I have only noticed it this season since it’s the only time I run my climate control. Z1 responded to my inquiry and said there shouldn’t be any issues. I guess it’ll give me a reason to get a better exhaust soon!