by Geoff WayAfter-market exhaust systems and in my particular case custom built exhaust systems on post 1986 vehicles do require the inclusion of a Catalytic Converter in their design. A popular after-market purchase is a “Cat Back” exhaust which obviously retains the original Catalytic Converter but custom built systems may lead to replacing the original Cat, what then?

Tip # 1
The Toyota factory Cats as fitted to MR2's are very durable but the ceramic style internals as found in most after-market Cats' can prove to be a problem. If your fuel mixtures are a few percent too rich or too lean they can literally disintegrate the ceramic core. Damaged units must be replaced, the EPA fines for not having one fitted run into 5 figures.

Tip # 2
After-market Ceramic Core Cats can be purchased for about $220 or even less if you have good contacts. Wreckers do sell Cats from wrecked cars but check them first, a quick look will establish its condition. Tell tale melted material indicates a problem and you should be able to see light through the centre indicating that the gases can pass through easily.

Tip #3
If your exhaust rattles and you trace the rattle to the Cat, replace it immediately and check the downstream area of the pipes for dislodged pieces of the Cat internals, these broken pieces will restrict exhaust flow and therefore engine performance considerably, similar to the old potato up the exhaust pipe trick.

Tip #4
My AW11 Turbo has a full custom built exhaust system which includes extractors and 2.5” outlet system. This matches perfectly with the Holden Commodore Catalytic Converter (VL onwards) which has a 2.5” inlet/outlet and has flanges at each end to facilitate quick and easy replacements at any time.

These can be sourced from most wreckers for under $100 almost anywhere in Australia . They have a Ceramic Core so monitor its condition regularly if used.

Tip # 5
Zoom magazine Issue April/May 1997 did an article on Cats and indicated that the ‘High Flow' Cat from Exhaust Technology in Adelaide was the pick of the bunch. They supply flanged units for Holden Commodores and will supply a 3” inlet/outlet version. Phone 08 8272 7500

Bolt and flange installations such as mine come in handy, as a last resort on a trip or Rally you can remove the Cat, dislodge the pieces from your exhaust pipe, refit the empty Cat shell and complete the journey. Be sure to replace the Cat as soon as possible
In summary, a ‘Cat Back' exhaust modification that retains the original MR2 factory fitted Cat may be the best option. If you opt for a bigger outlet pipe and need to change the factory Cat for an aftermarket ‘Ceramic Cored' unit you may experience failure of the core as time goes by. Ensure that custom built systems use flange and bolt installation for the Cat to allow easy replacement.