Yep, makes a huge difference. The wife has a tweaked 89 LeBaron with a 2.5 turbo, which had no cat., but is in a very good state of tune. It did 1850 ppm Nox, 60 HC, .7% co. on the drive test. After I put a used convertor(40K) off a 98 GrandCherokee on it it w... Login to read more.