I removed mine but am concerned over the higher heat. Wrapping sounds nice and looks the works if done right - but will it not subject the tubing to too high a heat? Will the manifold not crack? Has anyone been running this way for long time on original manifold and can testify this holds and is reliable?
Another note - my two front cats are dying. Is this a possible result of the heat shield being off? They be rattling like mad when cold. If I get rid of their innards and have a tube instead - will it pass emissions?
No it won't crack if wrapped, That's assuming that the manifold is healthy! The manifold will get up to temperature a lot quicker but wont get any hotter beyond that than it did before... Exhaust gases escape and move quickly so don't get a chance to increase the temperature beyond the manifold's design specifications. You have to remember they have been designed to get white hot at the most extreme revs over long periods on a test bed... They don't even glow red hot in real world driving conditions. What happens once wrapped, is the rest of the exhaust components get up to temperature a lot quicker due to radiated heat... In effect you will move the heat further down the exhaust system and keep it away from where it shouldn't be under the bonnet area which naturally reduces power due to less dense air in the induction system and makes the coolant and oil system work a little harder than it should do originally due to increases the ambient temperature... Cats like to be hot as that is when they work at their best efficiency, they can't do their job properly until they reach optimum temperature anyway.
You have to remember that the original heat shield is just that, a cheap shielding that isn't very effective compared to wrapping but installed for that very reason, to reduce some of the ambient temperature in the engine bay.
Cats have a shelf life, they don't last forever... Removing a manifold heat shield wont have any bearing whatsoever on the Cats apart from them taking a little longer to heat up to optimum operating temperature. They are rattling due to the break down of the components inside, it happens eventually to all Cats.
As for removing the Cat, well that all depends on your emission law requirements in your country, how efficient your car is, how clean the emissions are now.
I personally wouldn't recommend de-catting the car for those reasons, there is no way of knowing if it will pass a gas test afterwards with a de-cat pipe.
I would certainly consider replacing the cats ASAP if they are rattling before they start to break down into bits, clog the exhaust and cause excessive back pressure in the engine.
The chances are, once they are replaced, the car may run better, have more power and better fuel economy which will end up paying for themselves in a few months of driving anyway
Hope this answers your questions