HJS logoMilltek Sport Hi-Flow Sports Catalysts

Your original catalytic converter will typically have 400 or 600 cells per square inch (cpsi), these original cats are restrictive in their flow, typically allowing an open area of around 55-65%.

A Milltek Sport Hi-flow Sports Cat which will be fully integrated into a large bore downpipe, has only 100-200 cpsi depending on application. These cats have an open area of between 75-85%, thus reducing back pressure substantially and increasing flow rates, all very desirable for extracting more performance, especially on turbocharged engines. Emission levels are maintained at legal limits by careful selection of the volume of the metallic substrate. Lambda probe positions remain unchanged from the original equipment.

Milltek Sport Hi-flow Sports Cats work exceptionally well on re-mapped (chip tuned) engines. See below for an example of the power and torque gains that can be achieved.

Milltek Sport Hi-flow Sports Cats are made from a special stainless steel containing aluminium (called 'Fecralloy'). This material was developed in England in the 1970's specifically to provide resistance to oxidation at very high temperatures.

The material is used as a very thin strip (2 thousandths of an inch) and is coiled together to make a honeycomb structure. Because the metal strip is so thin, the honeycomb has a very low flow-obstruction. To reduce the flow-obstruction even further, the honeycomb is made with 100 or 200 'cells' (i.e. channels) per square inch compared with 400 or 600 per square inch for a standard catalyst.

The result is that about 85% of the total cross-section is open. The honeycomb is held together by using a special nickel-based brazing material which is applied in a vacuum. The finished honeycomb is then coated with Aluminum Oxide, some rare earth metals and Platinum and Rhodium. The Platinum and Rhodium are applied at a rate of 25 grams per cubic foot, which compares with between 5 and 10 grams per cubic foot for typical US aftermarket items.

It is normal practice in Europe to use much higher quantities of precious metals on catalysts, because European gasoline has more impurities in it which gradually poison catalysts. If catalysts with such high levels of precious metals are used with US fuels, the post-catalyst emissions are extremely low and the durability of the catalysts is very good indeed.

Audi S3 1.8T Hi-flow Sports Cats Performance Graph

The following graph show the power increase when using a Milltek Hi-flow Sports Cat (in conjunction with a remap) over a standard car with a standard catalytic converter.

PLEASE NOTE: Milltek Sport hi-flow sports catalysts are manufactured from the highest quality materials and built with maximum performance and longevity in mind. However, they are designed to work specifically in conjunction with other Milltek Sport products and should not be used on their own (with the OEM exhaust system) or with other manufacturers exhaust systems. If the Milltek catalysts are fitted with non-Milltek exhaust systems, we are unable to provide any guarantee regarding noise quality, fit, performance or warranty against their operation.