CATS CAN BE A PROBLEM
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.
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
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.