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    • Fabspeed argues going catless is not always necessary and you can lose power compared to sport cats on modern platforms such as McLaren, Porsche, Ferrari, etc.

      The conventional thinking is that going catless (ditching your catalytic converters) is best for power. That traditionally was the case but modern motors adjust so many parameters so quickly and are built for such efficiency that you can actually lose power by getting rid of the cats.


      Frankly, with German HJS 200 CPSI catalytic converters or sport cats you can have 93% of the flow of going catless. That means there is truth to Fabspeed's argument.

      Look at this 991.2 GT2 RS and what happens when going catless without any software tuning to accompany it as tested by 311RS.com:

      Porsche runs a heavily torque-based control strategy with it’s ECU. Just because there is a reduced back pressure doesn’t mean the car will produce more power than the target torque value. The ECU will close the throttle, limit wastegate duty cycle, etc. to keep that targeted number exactly the same.


      The ECU did not like it. They lost considerable power up top and torque through the curve.

      Fabspeed makes a good argument especially in relation to McLaren platforms:

      Quote Originally Posted by Fabspeed
      Fabspeed Motorsport has the most long term experience with all these Mclaren models since we were the worlds very 1st company to design, engineer, and incrementally dyno develop exhaust on each and every Mclaren model since the launch of the Mp412C. Our exhaust systems use CAD Designed 3D proof of concept printed and then investment cast lost wax stainless steel inlets and maxflo cast outlets for all our or systems. Nothing is left to chance and our sole mission is "ultimate bespoke quality and maximum power and sports car sound" for all fellow Mclaren enthusiasts worldwide.

      Some facts- Mclaren catbypass pipes will give you a Check Engine light P420/P430 code on these cars. Often you can use simulators to keep the light off BUT its not guaranteed. The car runs 100% fine but you get a small light on the dash. Simulators give you a 50% chance of eliminating a CEL light.

      Fabspeed Motorsport has awesome record setting safe tunes for all these McLaren cars for stock, with highflow cats and also No Cats RACE system with no CEL Lights 100% guaranteed. All of our tunes are set up safely for 92 to 93 octane pump fuel.

      Point of interest- in virtually all of our testing super highflow German imported Extra large diameter HJS 200 cell Catalytic converters make more absolute power and torque all across the RPM band than catbypass pipes. The HJS Catalytic converters FLOW 93% of a straight pipe and the cars don't go into overboost/ spike and the ECU doesn't try to trim and pull everything back as what happens when you install a catbypass pipes.

      Fabspeed Motorsport has tunes for all catted or no cat Mclaren cars. Whats interesting is that the power increase/ difference in ONLY +5HP by going tuned and catless. In our years of back to back dyno testing since 2010 with these cars catbypass pipes/competition pipes and with a tune you get only an additional +5HP more than a Mclaren with HJS German sport race cats with a tune on "same day same weather".

      So in essence a super premium quality German HJS 200 CPSI catalytic converter will give you all the power the car requires while passing emissions, you will have no Check Engine Lights, full readiness codes and have excellent sports car sound and maximum power all in one. The one and only thing is not all HJS catalytic converters are the same you have to get the largest HJS tri-metallic cores to get the 93% equivalent flow. Some companies offer small HJS cats and these restrict power and can have a CEL light as their is not enough surface area to scrub the exhaust.

      We have systems in stock and encourage anyone to come by for a shop tour and see the passion and teamwork that makes our systems world class. Fabspeed Motorsport is the only company to include 2200 degree Thermal military quality blankets on all Mclaren systems to allow for more engine protection, more power and less radiant heat in your engine bay.
      Going to sport cats while remaining emissions compliant can be a benefit versus going catless unless you have a tune that will take advantage of being catless. Even then, the percentage gained over modern sport cats is minimal.

      Look at this McLaren 570S.

      Sport cats:


      Cat bypass:


      The cat bypass pipes made a little more power but less torque and the ECU seemed to struggled a bit down low with the bypass pipes. A CEL (check engine light) without cats is inevitable and at that point you likely are losing power on the factory tune if the car isn't triggering various limp modes.

      Ideally, you want a tune to take advantage of the pipes whether running straight pipes or sport cats but the advantage of going catless is not what it once was. You also can lose power if not properly tuned and on the factory tune while triggering a CEL.

      Definitely something to keep in mind.

      This article was originally published in forum thread: Fabspeed argues going catless is not always necessary and you can lose power compared to sport cats on modern platforms such as McLaren, Porsche, Ferrari, etc. started by Sticky View original post
      Comments 21 Comments
      1. jcolley's Avatar
        jcolley -
        This is odd to me, almost like portions of the ECU aren't fully mapped. Most ECUs with torque management (fully acknowledge that I've never been within probably 50 miles of a McLaren DME) have a static torque map that is empirically derived from dyno testing representing n-m torque in a "load" vs "RPM" table. "Load" is often throttle plate angle (alphaN), MAP, or in BMW's case some "relative filling" value representing the combined 'holes' allowing air in (i.e. idle actuators, throttle actuators, EGR, seconadary air, etc).

        Any alteration in intake or exhaust head less (read back-pressure on the exhaust side) contributes a change to volumetric efficiency at various points in the VE fueling table. Properly calibrating the VE table after a modification (as opposed to relying on the closed loop fueling / lambda correction to un$#@! everything for you) requires altering all the steady state VE points on the VE table. Time consuming, especially on a reflash based tuning environment vs live tuning, but still possible. Once the VE tables are corrected, plugging in accurate numbers on the static torque maps allows everything to work backwards as designed to determine the correct "load" value target for the current torque request at the current RPM value.

        If the DME isn't producing greater torque at higher VE values, then it's an indication that either the torque management tables haven't been accurately altered to request more torque or the ignition tables haven't been optimized to take advantage of the higher VE values at the load site.

        All of that is with the assumption that VE actually increase at those load sites with reduction in exhaust head loss and that may not always be the case. It would be interesting to see if injector pulse-width actually went up or down as a result of the de-catting, that's the true indicator of VE changes assuming constant lambda targets. If so, then it can be determined that the lack of torque increase is a function of sub-optimal ignition advance and then it's off to determine of they are hitting the ignition targets or being pulled by other means (i.e. torque management.
      1. Vlps's Avatar
        Vlps -
        standalone ecu and catless pipes if you want real power
      1. Blown6's Avatar
        Blown6 -
        How can removing a restriction net you less power on a turbo car! The turbo is attempting desperately to expel its’ exhaust gases lol
      1. Mm3boost's Avatar
        Mm3boost -
        Click here to enlarge Originally Posted by Blown6 Click here to enlarge
        How can removing a restriction net you less power on a turbo car! The turbo is attempting desperately to expel its’ exhaust gases lol
        From what I gather from this article, the factory tuning in some of the higher end manufactures are so sensitive to backpressure changes that even though the exhaust system is freed without the restricitve cat, the reduce in backpressure is picked up by the ECU and it automatically adjusts (in a sense, it's power output) to reach target value backpressure levels prescribed from the factory.

        Not to say that removing the cat is hurting power, it's more just the factory tuning adjusting in modern day exocitcs. Like mentioned above, a proper tune and no cat should always make more power, unless we start seeing NHRA drag cars running cats no reason to think otherwise Click here to enlarge.
      1. Bowser330's Avatar
        Bowser330 -
        Click here to enlarge Originally Posted by Vlps Click here to enlarge
        standalone ecu and catless pipes if you want real power
        Does it have to be standalone? Wouldn't a fully capable flash tune be able to optimize the tables necessary to make real power as well?
      1. Stevenh's Avatar
        Stevenh -
        "Company that sells high flow cats says high flow cats are better!"

        ... In other news
      1. Torgus's Avatar
        Torgus -
        Click here to enlarge Originally Posted by Blown6 Click here to enlarge
        How can removing a restriction net you less power on a turbo car! The turbo is attempting desperately to expel its’ exhaust gases lol
        Exactly. /thread
      1. Batman's Avatar
        Batman -
        We’re not there yet but we’re slowly getting there. The days of us being able to remove the cats from our vehicles and drive around in cat-less exhaust systems are numbered. With each election cycle, it seems like we’re getting more tree huggers in government who would rather see everyone drive around in a Prius, Telsa, or ride a bicycle. It also doesn’t help matters that some of the major vendors for our vehicles don’t even make or carry catted exhaust systems. All you see on their website for exhausts are cat-less. I’m not saying that you will definitely pass emissions with an aftermarket catted exhaust system but at least it passes the “visual” test. That’s why I have to commend those few companies left that still make it a point and provide the option to run an aftermarket catted exhaust.
      1. Bowser330's Avatar
        Bowser330 -
        Click here to enlarge Originally Posted by Stevenh Click here to enlarge
        "Company that sells high flow cats says high flow cats are better!"

        ... In other news
        Click here to enlarge
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by Stevenh Click here to enlarge
        "Company that sells high flow cats says high flow cats are better!"

        ... In other news
        You could look at that way or look at as you don't have to violate emissions while maintaining almost the same power and torque as going catless.
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by Batman Click here to enlarge
        We’re not there yet but we’re slowly getting there. The days of us being able to remove the cats from our vehicles and drive around in cat-less exhaust systems are numbered. With each election cycle, it seems like we’re getting more tree huggers in government who would rather see everyone drive around in a Prius, Telsa, or ride a bicycle. It also doesn’t help matters that some of the major vendors for our vehicles don’t even make or carry catted exhaust systems. All you see on their website for exhausts are cat-less. I’m not saying that you will definitely pass emissions with an aftermarket catted exhaust system but at least it passes the “visual” test. That’s why I have to commend those few companies left that still make it a point and provide the option to run an aftermarket catted exhaust.
        No idea what someone negged you on this, here's a thumb up.
      1. kouzman's Avatar
        kouzman -
        IMO this is half a truth...

        I remember it back from my LAncer EVO days. untuned decatted car would run like $#@! simply because the zero restgriction would increase boost pressure and overboost too much and lean out the car, making it detonate thus pulling timing.

        The momment you tune it for decat the car makes more power that any catted system. Period!

        I think they also said that the 200 cpi cats are better than 100 cpi ones. They give a good supporting explanation as to why, but personally I still ordered a pair of 100 cpi motorport cats for my Inconel system. By the way they are also produced by the same German manufacturer and they are not too easy to come by... A 200 cpi almost guarantees a no check engine light and emissions passing, the 100 cpi might need some work the the location of the o2 sensors, and the test pipe? well, that's a different discussion...

        For maximum power on a tune I would go catless every single time.
      1. s13viper's Avatar
        s13viper -
        Physics is physics, when tuned there is no way catless can be worse at any stage. I don't care what anyone says, when tuned tp take advantage of it, catless is better everytime....

        I can believe it if throwing them on a stock ecu car, but who is going to do that.
      1. kohjul's Avatar
        kohjul -
        It shows that they dont tune the car correctly. It seems the tune doesnt turn off the closed loop system therefore it make the car run rich and lose performance. Right tune will make a big difference in power compare to any rated cat system. I’m sure that running HJS 200 cells still make the car Slower without a proper tuning and still run Rich compare to stock!
      1. maxnix's Avatar
        maxnix -
        Click here to enlarge Originally Posted by Batman Click here to enlarge
        We’re not there yet but we’re slowly getting there. The days of us being able to remove the cats from our vehicles and drive around in cat-less exhaust systems are numbered.
        You do not seem to understand that EPA standards are Federal Law and violating federal law is a felony,period. If the feds have probable cause to pull you over and you have tampered with a federally mandated emissions system so that emissions have even just increased, they can arrest you on the spot and haul you off to the clinker.

        It has been that way for decades. The way it is enforced is through emission testing so a vehicle that does not meet the federal standard for its year of manufacture cannot be licensed for the public roadways. I think CA has vehicles that can sniff your pipes once pulled over for any justifiable cause and if it fails, it can be impounded on the spot.

        But then marijuana is still a Schedule I felony drug under federal law also.
      1. maxnix's Avatar
        maxnix -
        Click here to enlarge Originally Posted by s13viper Click here to enlarge
        Physics is physics, when tuned there is no way catless can be worse at any stage. I don't care what anyone says, .....
        And you never saw LA in the Sixties.
      1. maxnix's Avatar
        maxnix -
        Click here to enlarge Originally Posted by Sticky Click here to enlarge
        You could look at that way or look at as you don't have to violate emissions while maintaining almost the same power and torque as going catless.
        That's the deal, you will have as much power on tap as your engine can produce except at top RPM. If everyone possessed this self indulgent streak to forego emission controls to be able to claim the last 5% of horsepower at peak RPM that they will seldom use on the street, the world would be a noticeably more toxic place. I give you Beijing, Delhi, Mexico City and other large urban areas that are choking from industrial pollution costing most residents years of less life. Emissions from vehicles just do not need to be added to such polluted environments.

        Remember, we all share the same air. It is not just we humans but the whole ecosystem.
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by maxnix Click here to enlarge
        Remember, we all share the same air. It is not just we humans but the whole ecosystem.
        Well it's a good thing I don't like people.
      1. Urmom's Avatar
        Urmom -
        Lol, sounds like me
      1. Stevenh's Avatar
        Stevenh -
        Click here to enlarge Originally Posted by maxnix Click here to enlarge
        That's the deal, you will have as much power on tap as your engine can produce except at top RPM. If everyone possessed this self indulgent streak to forego emission controls to be able to claim the last 5% of horsepower at peak RPM that they will seldom use on the street, the world would be a noticeably more toxic place. I give you Beijing, Delhi, Mexico City and other large urban areas that are choking from industrial pollution costing most residents years of less life. Emissions from vehicles just do not need to be added to such polluted environments.

        Remember, we all share the same air. It is not just we humans but the whole ecosystem.
        I was recently catless for about two weeks. My girlfriend was driving behind me one day and mentioned my car reeked of exhaust which I find to be pretty embarrassing. I love fast cars, but my days of loud exhausts and fumes are long behind me. I put the secondaries back in, the smell is gone, and the butt Dyno noticed zero difference.