Performance difference between a sports catalyst and decat pipe

Tuning guide "Sports Cats vs de-cat pipe"

Sports Cats vs de-cat pipe Guide

Should you go with a decat, or sports cat?

The catalyst (also referred to as a pollution or smog control) resides inside the exhaust. Its job is to create cleaner emissions by causing a reaction which reduces the CO2 and NO2 in the exhaust.

Because they are constructed of a matrix they impede the flow of exhaust gases and have been blamed by many as power stealers. What options are out there that regain this robbed power?

What is a sports or performance catalyst?

Typically, a sports catalyst is bigger to meet the increased flow rate necessary to maintain performance levels.

The catalyst has long been seen as a significant adversary of your vehicle's power production, but does reality bear this out?

Weight is another factor to consider, and a sports cat is often lighter than a conventional catalyst.

While the majority of sports cats are direct replacements, some have a larger bore capacity and would be better suited to a vehicle that has had a sports exhaust modification.

On smaller engines, the improvements in power will be negligible. On bigger engines, power improvements of between 4 and 10bhp are possible. Generally, the more power a vehicle produces, the more advantage a sports cat will provide.

Primarily there are 2 options to get faster flowing gases through the exhaust:-

What is a decat?

The first and easiest is referred to as a de-cat or decat pipe .

It is quite simply a pipe that sits where the catalyst should go and effectively the entire catalyst is removed. What are the drawbacks of  a de-cat?

To begin, we should note out that in the majority of nations, counties, and states, removing a catalyst is unlawful and should thus be considered an off-road modification; nonetheless, certain tracks are requiring pollution controls in select situations.

Many people like go for a de-cat pipe, test pipe or catless exhaust mod. This is a pipe that is installed in lieu of the catalyst, allowing exhaust gases to flow freely.

It is illegal in most states and countries unless your car can still meet its stringent emissions requirements without one.

Many people swap back the catalyst at the time of the annual test to obtain a "roadworthy and safe" certificate but the Police are increasingly using spot checks at the road side to catch people out.

Some engines will also have a probe further up the exhaust from the catalyst and if this reports 'dirty' exhaust fumes it will adjust the ignition timing typically running the engine lean.


While a de-cat is a cost-effective alternative, it does have certain downsides. In certain automobiles equipped with O2 sensors, you will produce a defect in the ECU, resulting in a dash warning or, in the worst-case scenario, damaging the car's performance, forcing limp home mode or causing starting troubles.

Alternatively, the engine may elect to consume less fuel owing to the quantity of unburned oxygen or residual particles. This results in the engine running lean.T his will result in a loss of power and could even cause the ecu to go into a limp home mode.

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Other vehicles have the Lambda or O2 sensor before to the catalyst and hence may operate without a de-cat pipe.

What are sports catalysts?

The second and most professional option is a sports catalyst.

These are manufactured to higher tolerances than the OEM ones and have much better flow characteristics.

The drawbacks of the sports cats are usually the cost but in real terms they cost little more than a standard original brand catalyst.

When you put a car on a rolling road what sort of results can you expect to see?

Car Tuning Tips took a Mitsubishi Evo IV onto a rolling road and the baseline power with the original catalyst was 295bhp. With the decat pipe this increased to 305 bhp and then when the sports catalyst was introduced power reached 304 bhp.

So we have to conclude that there is very little performance difference between a sports cat and a decat.

The standard EVO catalyst is actually very good which is why we see little gain between them but on more humble engines power gains reach around 5-10% higher.

If your catalyst needs replacing we would strongly recommend that you source a suitable sports catalyst rather than going for an illegal decat option.

If you are using the car off road then the decat would be the sensible and most cost effective option open to you.

Why do people believe that cats are stealing your power?

Many individuals believe the widespread myth that a catalyst is the nemesis of your car's power.

This is mostly due to the experiences of those who received early catalysts.

This occurred in the United Kingdom around 1992. To meet rigorous pollution standards, manufacturers developed the catalyst and began measuring emissions using the Lambda sensor.

To reduce pollutants and increase fuel efficiency, the majority of manufacturers detuned their engines. When comparing a pre-1992 car to a pre-1992 vehicle, the pre-1992 vehicle will often seem to be more powerful.

Automobiles manufactured after 1992 have improved fuel efficiency. Thus, the catalyst had a little effect on the car's power output, with the majority of this being due to the manufacturer's newest economy mapping.

Catalyst design and construction have advanced significantly since their inception, and there is nothing to gain for the majority of current automobiles.

Due to the fact that the increase in power is only 4-10 bhp on all but the most powerful engines, we cannot suggest this upgrade unless your engine already produces more than 200bhp or your power band is extremely high in the rpm range, as is the case with many VTEC engines.

If, however, your catalyst requires replacement, we highly advocate the advantages of a sports catalyst; you may as well take advantage of the added performance, since the cost is often comparable to that of a conventional OEM catalyst.

Because the costs of an original catalyst and a sports catalyst are so close, you may as well invest the money on a high-performance alternative.

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Your Constructive comments on this article

14 Responses to “Sports Cats vs de-cat pipe”

  1. robin says:

    i have a decat pipe, also with a sports cat on my janspeed twin exit exhuast.. so i got best of both worlds and power because my decat is racing rep adding 12 bhp (dyno tested) with the sports jansped cat also adding more power ( Dyno tested again)

    so if you can afford both its so worth it

  2. hilldawg says:

    lol your clueless mate, why lie? you cant have a decat and a sports cat at the same time they replace the same piece of pipe haha….

  3. Moe says:

    Im pretty sure what robin meant was having bought both but not on at the same time e.g sports cat for mot purposes and decat for the rest of the year or for the race track.

  4. scooby says:

    A decat pipe and a sports cat …. WOW – how did you manage to fit them together ?!

    Does this mean that the end of your tail pipe sticks out further than it should 😉


  5. simon says:

    can somebody help? i bought this toyota celica impo, the problem is that the exhaust system is too loud, any ways to bring the exhaust sound down? it has a hks induction kit.

  6. Brett says:

    Best to visit an exhaust centre and let them take a look at it, also the induction kit won’t help on the noise front.

  7. josh says:

    wanting to fit decat to my astra vxr, it will go into limp mode becasue its new and ecu is the ultimate boss. someone said about o2 extender to stop it doing this, any ideas what they mean?

  8. Andy says:

    Why is he clueless? You can run a decat 2nd cat pipe on an impreza, while keeping the cat in the downpipe, or having a sport cat downpipe in place.
    The second cat can be removed for road use also if a sportcat downpipe or original downpipe cat is used, as the prodrive ppp pack cars have this without being illegal or failing mot’s.

  9. Alex says:

    A decat pipe does provide extra power, but the noticeable difference is when your car has done more than 160000Km’s. the power difference is largely ralated to the clogging of the catalytic converter.

  10. paranoidpolska says:

    Bro you can either run a cat delete or sport cat(s). You’re not doing both, regardless of the location of components on your exhaust system. Catless is gonna flow better, but then you have to pay for O2 Sensor Sims (~$200+) or use spark plug non-foulers ($5 at Advance) to keep your MIL light off and pass emissions. I think this article was just written by Al Gore. However, I agree the sport cat can’t be very restrictive. It utilizes ceramic honeycombs rather than a fine mesh grate of precious metals. You guys sound like a bunch of car n00bs driving riced out Celicas and Integras. Why even bother tuning a car with 90hp. Get a real car like an STI, M3, S4, Corvette, or Shelby before you go blowing money on an exhaust lol.

  11. Stephen Smith says:

    I’m thinking about going to stage two on my ‘hairdressers’ car. A fiesta St mk 7 (16 plate)
    It’s currently got all the Mountune upgrades ready for stage two except the map and the sports cat. Thing is I’m thinking about revo and someone said to me that I wouldn’t need the sports cat as the modern cats are good enough to accommodate the power. It’s a good saving but if it’s the difference between say, 5 to 10 bhp then I’ll pay it.
    Also does a new dump valve (recirculating, not atmospheric) make sense. Turbo smart maybe?

  12. Charlie of says:

    In the UK recent changes in the UK law mean all cars petrol or diesel must have original or H suffix replacement cat where fitted to the vehicle at manufacture.
    The MOT testers currently do not have to actively look for it, but no doubt this will change.

    While there is a small gain in BHP from decat or sports cats, from experience you are better spending your money on a proper tune, if possible on a rolling road.

    Fully service the car, and if being used on track days or off road, use the best fluids and parts you can afford and service more regularly.

    Use a hi flow drop in panel if conditions are not dusty. If they are dusty, stick to the paper. Beware of your vehicles air intake system, especially those that are low to the ground. While cold air systems can help, look at the design and where your engine hot spots are, such as manifolds. Do not expect to see big gains on small engines for CAI systems, just is not going to happen.

    Look at the benefits of EGR delete where fitted, but these may become mandatory at some stage in the future so do not bin it.

    Consider fitting silicone hoses on the induction and intercooler system. Word of caution though do not use a non branded version. Silicon hoses are considered better at handling the increased temperatures of tuned engines. When fitting check pipe clips after a couple of runs, as the hoses bed in when warm. Note OE rubber hoses are usually ok for mild tunes and in some cases better than silicone.

    While going quick is good, do not forget stopping is too, so check your pads and discs regularly.

    Final word – Tyres the best performance car in the world is going to go no where on poor quality tyres. It makes sense, think about where all that torque from your engine is going ?

    Join an owners forum if possible, there are like most things good ones and bad ones, but you will see from search engine results the most popular on different topics concerning your car.

    Most of all enjoy your car, going fast means you are responsible for the safety your self and other road users, doing so in a properly prepped car makes a difference to your driving enjoyment, and the environment.

    Ten horses on and EVO IV says it all really, what you did not mention was what difference it made to torque in the engine and torque to the wheels.

  13. Dave swaine says:

    I’m running an 03 jaguar STR lots of mods already done currently 441bhp at the crank & 431bhp at the rear wheels, mods done are 10% upgrade pulley, NGK iridium race spec plugs, KnN air filter, Caldoofy stainless hand made intake pipe, Adamesh cat back exhausts, I’ve been offered a pair of sports cats at an excellent price and wondered what benefits they would bring to an already beast of a car? Uk based

  14. mike says:

    Funny how so many experts on here do not realize many cars come with dual cats, one off the header, and another downstream. Typically only the first is metered. On a V8 it could be 4 cats total as with my Aston Martin. So you replace the first cat with a sport cat so you don’t throw codes, then the second cat with a test pipe. Bottom line though, if you can’t afford a high flow cat, you have bigger issues than going a little faster/louder.