I have purchased a Magnaflow 49483 direct-fit OEM cat pipe and the ubiquitous fleaBay shorty header most people recommend. When inspecting the connection at the header outlet/cat pipe inlet, I verified that they do fit each other, however, every thread I've read about adding the cat pipe says that the Magnaflow-provided donut gasket doesn't fit to the OEM EX exhaust manifold, so forum members commonly recommend using the OEM EX donut gasket instead. Again, both the Magnaflow and the header are advertised as fitting the OEM EX exhaust system- just to clarify.

The trouble is that online searches reveal that the OEM EX exhaust manifold outlet is 2-inch. My eBay shorty header has a 2.25-inch (O.D.) outlet diameter. Am I misreading something somewhere? I'm in search of the correct gasket and was wondering if anyone else has encountered the same issue, as I haven't seen very many (if any) threads about folks combining this Chineseum header with the Magnaflow 49483 - presumably due to the prohibitive cost for not much gain.

I went to Autozone today with the header and cat pipe in-hand and walked out with the following:

Fel-Pro p/n: 61089
Inside Diameter: Approximately 2.333 inches (59 mm)
Outside Diameter: Approximately 3.124 inches (79 mm)
Thickness: About 1 inch (26 mm)
Material: Steel

Think this'll work? There's no way a 2in OEM EX donut is going to fit around the header outlet (which is 2.25 O.D.). The widest point at the cat pipe flange is ~3 inches.

 

(ADDENDUM):
A nice fella at the D-Series forum pointed out that I have a one in two chance of the right gasket as Honda only uses two sizes... I think I know where I went wrong here. The header outlet sits on top of the donut rather than the donut slipping around the outlet? Here's the o.d. of the header outlet: