Running CATS vs. CATLESS debate settled...
10-03-2017, 10:01 PM
#1
Rennlist Member
Thread Starter
Running CATS vs. CATLESS debate settled...
Hey gents,
Been away from here for a while with a couple of track events and a bunch of work away from car. Over the years, there has been a lot of debate over horsepower given up by running CATS vs. bypass pipe, or conversely hp gained by running bypass pipes. The general consensus is that going to catless will yield an increase in Hp and in most cases that is correct. As I have recently found out, and confirmed, to my surprise you can actually have your cake and eat it too.
Let me caveat this by saying that NOT all cats are the same even when comparing 100CPI cats from the same manufacturer. Most people do not understand this simple fact but you can just look at the HJS website and see all their various offerings of 100 cell Motorsport cats with various ratings from Cup catalysts, UL (ultralite) catalysts, or the top the line PE high flow catalysts. Sizes available are from 93mm diameter all the way to 153mm diameter and prices from $400 to in excess of $1000 per core. Hp rating for the various cores range from 360hp/pair all the way to 900hp/pair on the large diameter versions.
I am not affiliated with HJS in any way but they are the premier supplier of catalysts used by the finest OEMs across the globe. The street catalysts are the HJS "HD" 200CPI versions. HJS is also the premier supplier of Motorsport catalysts. The German company Emitec actually makes the top of the line PE catalyst motorsport 100CPI cores for HJS. The "PE" catalysts are the highest flowing Motorsports cores available and that is why I chose to use these on my exhaust when I had it built 3 years ago. You can see them in the pics below:
The current exhaust I'm running and used for testing is a custom 3" flow through exhaust utilizing the HJS/Emitec Motorsport 100CPI 130mm x 100mm PE cores. These 5.2" diameter cores are rated at 350hp each / 700hp for the pair. I have run these cats for 3 track season with almost 70hr track hours on them. They have performed flawlessly and the cores look perfect even after all this track time. I have measured temps of these cores at the end of a track session at well over 1000F with on track temps likely in excess of 1500F. In other words, these suckers are tough as they are rated by Emitec in excess of 1700F! We dynoed 621whp and 720wtq with these catalyst last month. For those wondering, these cores have always passed every emission sniffer test with flying colors and are fully OBD compliant. With that said, many guys in my area have run the HJS 200CPI HD catalysts and most have experienced core failures after a few track seasons as they are not designed to deal with the high heat of track use.
Two weeks after the dyno above, I installed a set of large 3.5" cat bypass pipes in place of the Emitec PE CATS for an apples to apples comparison. This was an easy swap as the CATS and bypass pipes are V-banded in to the exhaust. We dynoed the car on the same dyno with the bypass pipes and expected to find a small increase in power. To our surprise, we actually lost a small amount of power and torque thoughout the power band (about 3-5 hp on the avg.) There was a tiny 1hp increase with the bypass pipes yielding 622hp near the upper end of the rpm range at 7400 but overall a small loss. The overlayed dyno graphs were virtually identical indicating absolutely zero difference in spool up with or without the cats.
The ambient temperatures were a couple of degrees higher on the second dyno with the bypass pipes along with slightly higher intake temps. As a result, I would call the slight loss attributed to the higher temps and the variance within the dyno and thus statistically insignificant. In other words, the 3.5" bypass pipes did not produce any gains nor any statistical losses. Other things I would note is the fact that there was zero detectable increase of exhaust note or any appreciable increase in turbo whistle that I could make out. This is clearly an indication of how well the PE cores flow.
Now many people will ask how it's possible that 100CPI cores can flow as much as a large 3.5" bypass pipe. It's very easy if you realize that the larger diameter of core you have, the more "voids" you will have over the area of the catalyst core. Naturally, as you increase the diameter of the core, you are increasing it's flow capacity. Just eyeballing it, I would say that on a 130mm (5.2" core) PE core you will have a void area equal to or in excess of a 3" bypass pipe. In other worlds, there should be little if any flow loss. This theory is directly confirmed by the above dyno test. The byproduct and benefit of increasing the diameter of the catalyst core is also the fact that you have more surface with more precious metal which effectively gives you more ability to scrub the exhaust gases and maintain years of trouble free use from a high flowing catalyst. In other words, these large high end cores probably have as much if not more precious metal in them than your typical small 200-400CPI street or OEM core thus ensuring lond term durability.
The obvious downside of using these high end 100CPI HJS/Emitec Motorsports catalysts is the high costs which is why you do not see any aftermarket exhaust manufacturer (with the exception of Europipe) use these as just the cats would add close to $2000 to the price of the exhaust. This is why you typically see much smaller 100mm catalysts used which can be had for fractions of that price. When smaller cats are used, they are typically going to be 200CPI to have to ability to scrub effectively. Naturally, smaller denser cats will have much greater back pressure, retain more heat, and in turn reduce performance.
In summary, if you are running an engine in the 600-650whp range and want to remain emission compliant without giving up any performance whatsoever, with the right cats, you can have your cake and eat it too. If running even higher HP, you can go with even larger PE cats that will remain 100% efficient to 900+hp. I am currently having another custom inconel/Ti exhaust built and it will employ even larger 143mm/5.66" HJS PE Motorsport cores. That is as large as we can go due to packaging constraints but these will give another 100hp of headroom maintaining 100% efficiency to 800hp. I would imagine that any reputable exhaust manufacturer can get these catalysts and build them into their exhaust if you specifically request them.
The last item of note I will add is with regards to the OEM secondary O2 sensors. As we all know, the pre-cat primary wideband Bosch 02 sensors are responsible for Lambda control. Many here however have also argued that the post cat sensors have some type of effect on controlling Lambda and fuel trims. There is nothing published by Porsche that would support this however. I have looked and analyzed Lambdas both when running cats and bypass pipes and can not detect any difference in Lambdas whatsoever. Zero, zilch, none. The secondary sensors are strictly there for cat efficiency purposes from what all data indicates. I am running two sets of primary wideband O2 sensors, one set of the OEM wideband Bosch sensors, and the other set being the 4.9 wideband Bosch sensors that are used by my Motec set up. The 4.9s are a newer more accurate sensor than the OEM widebands. Since switching to the 3.5" bypass pipes, I have also used a simple FVD 02 extender. It's a very nice German product with excellent machining. I've looked at many extenders and most are cheap Chinese parts that are sold on Amazon. Again I would say that not all are the same and you get what you pay for. With over 500 track miles running catless, I have not yet tripped any CEL which indicates that the FVD extenders work. All readiness codes show as "PASS" so these do the trick. You can see them in the pic below.
Hopefully this settles the catted vs. catless debate.
Cheers!
Here is the latest version of the HJS Emitec 100 CPI Motorsport catalysts which I'm going to be using on my new exhaust. These are even larger at 145mm diameter (5.7") and are rated at 400hp per core at 100% efficiency.
[
Been away from here for a while with a couple of track events and a bunch of work away from car. Over the years, there has been a lot of debate over horsepower given up by running CATS vs. bypass pipe, or conversely hp gained by running bypass pipes. The general consensus is that going to catless will yield an increase in Hp and in most cases that is correct. As I have recently found out, and confirmed, to my surprise you can actually have your cake and eat it too.
Let me caveat this by saying that NOT all cats are the same even when comparing 100CPI cats from the same manufacturer. Most people do not understand this simple fact but you can just look at the HJS website and see all their various offerings of 100 cell Motorsport cats with various ratings from Cup catalysts, UL (ultralite) catalysts, or the top the line PE high flow catalysts. Sizes available are from 93mm diameter all the way to 153mm diameter and prices from $400 to in excess of $1000 per core. Hp rating for the various cores range from 360hp/pair all the way to 900hp/pair on the large diameter versions.
I am not affiliated with HJS in any way but they are the premier supplier of catalysts used by the finest OEMs across the globe. The street catalysts are the HJS "HD" 200CPI versions. HJS is also the premier supplier of Motorsport catalysts. The German company Emitec actually makes the top of the line PE catalyst motorsport 100CPI cores for HJS. The "PE" catalysts are the highest flowing Motorsports cores available and that is why I chose to use these on my exhaust when I had it built 3 years ago. You can see them in the pics below:
The current exhaust I'm running and used for testing is a custom 3" flow through exhaust utilizing the HJS/Emitec Motorsport 100CPI 130mm x 100mm PE cores. These 5.2" diameter cores are rated at 350hp each / 700hp for the pair. I have run these cats for 3 track season with almost 70hr track hours on them. They have performed flawlessly and the cores look perfect even after all this track time. I have measured temps of these cores at the end of a track session at well over 1000F with on track temps likely in excess of 1500F. In other words, these suckers are tough as they are rated by Emitec in excess of 1700F! We dynoed 621whp and 720wtq with these catalyst last month. For those wondering, these cores have always passed every emission sniffer test with flying colors and are fully OBD compliant. With that said, many guys in my area have run the HJS 200CPI HD catalysts and most have experienced core failures after a few track seasons as they are not designed to deal with the high heat of track use.
Two weeks after the dyno above, I installed a set of large 3.5" cat bypass pipes in place of the Emitec PE CATS for an apples to apples comparison. This was an easy swap as the CATS and bypass pipes are V-banded in to the exhaust. We dynoed the car on the same dyno with the bypass pipes and expected to find a small increase in power. To our surprise, we actually lost a small amount of power and torque thoughout the power band (about 3-5 hp on the avg.) There was a tiny 1hp increase with the bypass pipes yielding 622hp near the upper end of the rpm range at 7400 but overall a small loss. The overlayed dyno graphs were virtually identical indicating absolutely zero difference in spool up with or without the cats.
The ambient temperatures were a couple of degrees higher on the second dyno with the bypass pipes along with slightly higher intake temps. As a result, I would call the slight loss attributed to the higher temps and the variance within the dyno and thus statistically insignificant. In other words, the 3.5" bypass pipes did not produce any gains nor any statistical losses. Other things I would note is the fact that there was zero detectable increase of exhaust note or any appreciable increase in turbo whistle that I could make out. This is clearly an indication of how well the PE cores flow.
Now many people will ask how it's possible that 100CPI cores can flow as much as a large 3.5" bypass pipe. It's very easy if you realize that the larger diameter of core you have, the more "voids" you will have over the area of the catalyst core. Naturally, as you increase the diameter of the core, you are increasing it's flow capacity. Just eyeballing it, I would say that on a 130mm (5.2" core) PE core you will have a void area equal to or in excess of a 3" bypass pipe. In other worlds, there should be little if any flow loss. This theory is directly confirmed by the above dyno test. The byproduct and benefit of increasing the diameter of the catalyst core is also the fact that you have more surface with more precious metal which effectively gives you more ability to scrub the exhaust gases and maintain years of trouble free use from a high flowing catalyst. In other words, these large high end cores probably have as much if not more precious metal in them than your typical small 200-400CPI street or OEM core thus ensuring lond term durability.
The obvious downside of using these high end 100CPI HJS/Emitec Motorsports catalysts is the high costs which is why you do not see any aftermarket exhaust manufacturer (with the exception of Europipe) use these as just the cats would add close to $2000 to the price of the exhaust. This is why you typically see much smaller 100mm catalysts used which can be had for fractions of that price. When smaller cats are used, they are typically going to be 200CPI to have to ability to scrub effectively. Naturally, smaller denser cats will have much greater back pressure, retain more heat, and in turn reduce performance.
In summary, if you are running an engine in the 600-650whp range and want to remain emission compliant without giving up any performance whatsoever, with the right cats, you can have your cake and eat it too. If running even higher HP, you can go with even larger PE cats that will remain 100% efficient to 900+hp. I am currently having another custom inconel/Ti exhaust built and it will employ even larger 143mm/5.66" HJS PE Motorsport cores. That is as large as we can go due to packaging constraints but these will give another 100hp of headroom maintaining 100% efficiency to 800hp. I would imagine that any reputable exhaust manufacturer can get these catalysts and build them into their exhaust if you specifically request them.
The last item of note I will add is with regards to the OEM secondary O2 sensors. As we all know, the pre-cat primary wideband Bosch 02 sensors are responsible for Lambda control. Many here however have also argued that the post cat sensors have some type of effect on controlling Lambda and fuel trims. There is nothing published by Porsche that would support this however. I have looked and analyzed Lambdas both when running cats and bypass pipes and can not detect any difference in Lambdas whatsoever. Zero, zilch, none. The secondary sensors are strictly there for cat efficiency purposes from what all data indicates. I am running two sets of primary wideband O2 sensors, one set of the OEM wideband Bosch sensors, and the other set being the 4.9 wideband Bosch sensors that are used by my Motec set up. The 4.9s are a newer more accurate sensor than the OEM widebands. Since switching to the 3.5" bypass pipes, I have also used a simple FVD 02 extender. It's a very nice German product with excellent machining. I've looked at many extenders and most are cheap Chinese parts that are sold on Amazon. Again I would say that not all are the same and you get what you pay for. With over 500 track miles running catless, I have not yet tripped any CEL which indicates that the FVD extenders work. All readiness codes show as "PASS" so these do the trick. You can see them in the pic below.
Hopefully this settles the catted vs. catless debate.
Cheers!
Here is the latest version of the HJS Emitec 100 CPI Motorsport catalysts which I'm going to be using on my new exhaust. These are even larger at 145mm diameter (5.7") and are rated at 400hp per core at 100% efficiency.
Last edited by powdrhound; 09-21-2018 at 07:27 PM.
10-03-2017, 10:20 PM
#2
RL Community Team
Rennlist Member
Rennlist Member
Very thorough. Thanks.
10-04-2017, 12:08 AM
#3
Rennlist Member
+1!
This is what's so fascinating to me and why I'm so grateful for the info. I'm new to 996TT ownership, but I've been reading various car forums about modifying cars for a long time, and no one ever talks about this. The obvious answer is that no one wants to shell out what it takes for a proper setup, but kind of like forged wheels -- the only downside is cost. Those are the kind of engineering compromises worth saving up for. But if even the Porsche guys don't want to do it, you know the Honda guys aren't.
Also, while you're using high HP setups as your example, I think everything you lay out actually applies just as well to any HP range. Just spec out the appropriate model for your HP range (now I need to buy a $450 cat for the $450 exhaust on my Honda
).
The obvious downside of using these high end 100CPI HJS/Emitec Motorsports catalysts is the high costs which is why you do not see any aftermarket exhaust manufacturer (with the exception of Europipe) use these as just the cats would add close to $2000 to the price of the exhaust.
Also, while you're using high HP setups as your example, I think everything you lay out actually applies just as well to any HP range. Just spec out the appropriate model for your HP range (now I need to buy a $450 cat for the $450 exhaust on my Honda
).
10-04-2017, 12:25 AM
#4
Rennlist Member
Nice info.
Apart from the neutral performance in comparison to very high end 100 cell cats, any feedback on the 'annoyance' factor while catless? Smell in particular?
Also, i might alternately say 'You can have your cake and eat it too, but this particular cake ain't cheap!'
Apart from the neutral performance in comparison to very high end 100 cell cats, any feedback on the 'annoyance' factor while catless? Smell in particular?
Also, i might alternately say 'You can have your cake and eat it too, but this particular cake ain't cheap!'
10-04-2017, 02:40 AM
#5
Rennlist Member
Thread Starter
Nice info.
Apart from the neutral performance in comparison to very high end 100 cell cats, any feedback on the 'annoyance' factor while catless? Smell in particular?
Also, i might alternately say 'You can have your cake and eat it too, but this particular cake ain't cheap!'
Apart from the neutral performance in comparison to very high end 100 cell cats, any feedback on the 'annoyance' factor while catless? Smell in particular?
Also, i might alternately say 'You can have your cake and eat it too, but this particular cake ain't cheap!'
Last edited by powdrhound; 10-04-2017 at 03:00 AM.
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10-04-2017, 01:58 PM
#8
Rennlist Member
eh. Your dyno differences are well within the "errorbility" of the dyno. A 3-5 hp shift from run to run easily happens.
The biggest issue with any of the "high flow" cats is that they lose their effectiveness over time. Unfortunately that time is short too. It's not unusual to put a new set in and pass emissions, then when you need to go through again in two years, to fail.
There's a reason why they flow better and cost so much less than the stock OEM cats. They have nowhere near the same amount of heavy metals in them.
In short, if you're willing to pay to replace them periodically, you can have your cake and eat it to. Otherwise you're better served with putting test pipes in at the track and running the OEM cats on the street.
The biggest issue with any of the "high flow" cats is that they lose their effectiveness over time. Unfortunately that time is short too. It's not unusual to put a new set in and pass emissions, then when you need to go through again in two years, to fail.
There's a reason why they flow better and cost so much less than the stock OEM cats. They have nowhere near the same amount of heavy metals in them.
In short, if you're willing to pay to replace them periodically, you can have your cake and eat it to. Otherwise you're better served with putting test pipes in at the track and running the OEM cats on the street.
10-04-2017, 02:05 PM
#9
Rennlist Member
Kinda seems like you didn't actually read his post.
10-04-2017, 02:47 PM
#10
RL Community Team
Rennlist Member
Rennlist Member
^ LOL.
10-04-2017, 02:55 PM
#11
Three Wheelin'
I do a lot of flow modeling as part of my job and deal with flow restrictions on a daily basis. In our case the the main restriction is the turbo, it produces significant back pressure as part of it's job. So when you place a restriction down stream of it, it's effect is minimal. If you were to test the same cats on a high flow NA car, i would think the results would be very different.
The turbo system on our cars is a closed loop control system, so only at the edges of the control envelope will a small additional restriction have a significant effect as the control loop corrects for it otherwise.
Thanks John for providing a well thought out and data based analysis of your exhaust choices. I wish i had your budget for car stuff.
The turbo system on our cars is a closed loop control system, so only at the edges of the control envelope will a small additional restriction have a significant effect as the control loop corrects for it otherwise.
Thanks John for providing a well thought out and data based analysis of your exhaust choices. I wish i had your budget for car stuff.
10-06-2017, 09:04 AM
#15
Great write up John. My only really note though is cost. For most guys, running catless for the performance gains is the cheapest and easiest way. The cars you have here are huge dollar compared to what most system up and flow much better. Your typically 100 or 200 cell cat is quite a bit more restrictive than the ones you are using here.
I do appreciate the research, time, and money that went into this though and the results to show for themselves what is possible with the RIGHT kind of parts. Got to pay to play sometimes.
I do appreciate the research, time, and money that went into this though and the results to show for themselves what is possible with the RIGHT kind of parts. Got to pay to play sometimes.