Hi, I have a 4 inch single pipe on my car coming from 3" long tubes, and in the state I live now I need to add a cat converter to pass visual inspection.
I have yet to find a 4inch in/outlet high flow converter online.

Anyone else have something like this or know where I can get one?

So far, I'm only finding 4" diesels, and a 3.5" magnaflow spin flow.
I don't think its a good thing to put a diesel converter on a gas engine but haven't found out yet either what the real difference is in materials.

 

Why not put one 3" inch cat on each collector? This would obviously require modifying the y-pipe, but it is what I did. Since you have a 93 you have no after cat O2 sensors so there is no harm in having two converters.

 

Ditto. Pair of 3" Carsound cats, one in each branch of the 3" Y-pipe. Whole assembly was built by Mufflex and attached to their 4" catback. Converters were flanged so they could be dropped out for the track, and 3" Borla XR1 mufflers installed.