hi to everybody.
I have and issue with my just recently installed Magnaflow cat. conv. I have 06 G35 seda 6 MT. The car is california spec. But because I live outside USA in EU that is not an issue. But because I made mistake and brought my car 49 state version of cat conv. and the flanges are different from calif. spec.
Whe I found out it was too late to do anything and I did not wanted to send them back I decided to use my old OEM flanges that were welded to my new 49 state spec cat. conv. I am using OEM gaskets but there is still leak on exhaust and I have checked it several times no leak. But I can smell the leak in car.
There was said from magnaflow I cannot use 49 state version on california spec car? Why not? If there is difference in flanges, it is not problem but now I hear there is different gas sirculation, is that possible fix?
How can this cause exhaust gases leak if there is no visible leak?
What is the difference that I cannot use it with no problems?

Hello from the US!

A few thoughts: First, there should be TWO catalytic converters on your car (one on each side). Did you replace both?

I want to make sure I understand - You cut the flanges off your original cat and welded them to the new cat?

There could be several problems - the most likely, in my experience, is that the angle of the flange is not exactly correct. Exhaust systems and components are built in a jig, in order to keep everything at the correct angle and alignment. If it is off by a VERY tiny amount, there will be a leak. Exhaust leaks are not always visible - a tiny gap can allow a lot of fumes to escape - possibly on the top of the piping, where you cannot see.

The 49-state catalytic converter assembly is different from the California assembly (because California does stupid things ). Here's the difference:

Right side, 49-state converter for your car:


Right side, CA converter for your car:


I thin the smartest thing to do would be to purchase the correct model for your application, OR use a Magnaflow universal converter (since you are not subject to emissions testing).

We'll help you figure it out.

Yes I replaced both sides, product code 49144 and 49143. I think still that when there is leak even tiny hole, it would be black of dust-exhaust gases. As I have talked to exhaust experts even a needle head size hole makes several inch size dust on the surface that can be seen.
I want to make sure I understand - You cut the flanges off your original cat and welded them to the new cat? Answer-Yes.
I still do not understand how there can be leaks if everything is tight and no holes?