The good news is that, although replacement Audi S4 catalytic converters can be costly from your local dealership, aftermarket units (many times made by the same original equipment manufacturers) are substantially less expensive and can be purchased as direct-fit bolt-on units (assuming that the original converter was also bolted on) or weld-on units. Replacing your Audi S4 catalytic converter can restore power that has been lost due to a faulty original converter and will make your vehicle run better overall. In addition, a bad Audi S4 catalytic converter means that your exhaust is releasing harmful toxins into the atmosphere and environment, so getting a new one means you’re doing your part to keep the earth and its atmosphere clean.

Modern catalytic converters are much less restrictive than in days past, so much so that the antiquated (and illegal) method of "gutting" the converters of their internal structures has been deemed almost pointless on newer cars, as the performance gains are minimal, if any. Aftermarket high-flow Audi S4 catalytic converters are therefore a much better (and more responsible) choice for those seeking to upgrade their exhaust systems or replace a faulty converter.

So how do you know if your Audi S4 catalytic converter is on its way out? If your Audi S4 engine seems to be losing power or your temperature gauge reads a little high, one possible culprit could be that a rich condition is feeding excessive unburned fuel into the catalytic converter, which can overheat it as well as damage it. It is common to see your Audi S4 catalytic converter glowing orange/red when this condition is present. Another common sign of catalytic converter failure is the infamous "rotten egg" smell. Other common symptoms include: a lack of power, rough engine idle, or stalling. If you are replacing your Audi S4 catalytic converter due to any of the above circumstances, it is a good idea to also replace your oxygen sensor, since it plays a vital role in the air/fuel mixture ratio and may have also been damaged due to the same adverse conditions. Finally, physical damage can sometimes occur if a large rock or other object hits Audi S4 catalytic converter, resulting in a damaged ceramic core. This can often be heard, as smaller ceramic pieces will bounce around inside the converter housing. As you can imagine, this is often accompanied by a loss of power due to exhaust blockage.

Q: What is a hi-flow catalytic converter? Why buy one?
A: All stock catalytic converters are restrictive when it comes to exhaust flow, and they essentially place a choke hold on performance. The hi-flow catalytic converters on the market today have a higher flow capacity than factory units. Still able to pass emissions and gain horsepower, how can you go wrong with a hi-flow catalytic converter?

Q: How do you install a hi-flow catalytic converter?
A: There are two kinds of catalytic converters. The first are direct fit converters (no welding required) which have all necessary flanges and oxygen sensors just like the original equipment catalytic converters. There are also universal fit catalytic converters that are designed to be welded or clamped in place. Universal fit converters have the same flow characteristics as direct fit models with the same inlet and outlet diameter.