Decat vs sport cat

[willk86]

Sorry if this has already been covered millions of times...

Is there much loss in gains by going with a sports cat on a 3" downpipe?

I'll be using a standard cat back for now, looking at the pipeworx downpipes as they look like decent bits of kit plus I know a few people that have had stuff from then before, bikes and cars.

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[Dan_FR]

Pro's

• Gains in flow over stock
• Will pass an MOT with plenty of heat

Cons

• Doesn't flow as well as a decat so will sacrifice a few HP up top. How much depends on the individual setup
• Will pass 1 MOT, maybe the following year too with LOTS of heat. Then it won't and you'll either need a friendly MOT tester, a new sports cat or refit the standard one

Me personally - Decat everytime, refit standard annually if needed

[Manny_ED30]

Pro's

• Gains in flow over stock
• Will pass an MOT with plenty of heat

Cons

• Doesn't flow as well as a decat so will sacrifice a few HP up top. How much depends on the individual setup
• Will pass 1 MOT, maybe the following year too with LOTS of heat. Then it won't and you'll either need a friendly MOT tester, a new sports cat or refit the standard one

Me personally - Decat everytime, refit standard annually if needed

This is interesting Dan  - but say for those who run a sports cat on their daily and hard/spirited drives are far in between, would it still be the case of the sports cat only doing its job for so long until you need a friendly MOT tester?

[Dan_FR]

Yep. Why do you think the sports cats are so cheap compared with OEM quality - the quality of the precious metals inside is awful. They are made as cheaply as possible. Hey, you may be lucky and get 2 or even 3 years, who knows..... But you certainly wont get the same lifetime that you get from an original part

[Manny_ED30]

Ahh right, never thought of it like that in all honesty!

Always been abit skeptical about going decat as the noise increase from removing the cat may become abit of an annoyance.

My thinking was a sports cat BCS DP, front silencer delete with the variable tone back box would be a good set up, gains wise and noise. If I opted for this but with a decat, won't it be too loud?

[Dan_FR]

Hard to say whats too loud or not loud, everyone's tastes and preferences are different. Whats loud to me may be acceptable to you.

Mine has a decat and 2 full size silencers as its a daily that's used to shuttle my son to school with a 5 month in tow. Perfectly civil and quiet driven normally, not a great deal louder than standard, but with a nice note and quite a bit more volume on boost.

BCS cats are supposedly better quality than the likes of eBay specials but I've never used them. Ideally you'd need to get out in a few cars with BCS system and try before you buy.... Find someone local maybe, either on here, or try TFSI Tuning group on Facebook?

[f00glee]

I think I've seen in the BCS blurb that their sports cats have a "greater than" flow compared to the 3" pipework either side. So there is nothing to be lost in terms of performance by having the sports cat in place. I could be mistaken though, perhaps give Nige a call to confirm  The BCS cats in their images have "euro 5" engraved in them too - suggesting a certain level of efficiency.

[Manny_ED30]

Nige pointed out that the BCS cats are oversized to help with flow. Overall they look better quality than other cat DP's i've seen/been offered.

Driving in bumper to bumper traffic through the busiest parts of my city to and from work, the last thing I want is for people to turn their heads or they feel the vibration from the noise of my exhaust  when gently applying the peddle. - abit extreme I know but i've been in plenty of cars, for example my mates S3 with a decat, straight through miltek is only fun when planting it, otherwise annoying.

But I guess this is where you opted for the variable tone BCS to keep everything as close to stock sounding as possible?

[Powervalve Nige]

As a generalisation the quality of so called sports cats is something of a lottery to the uninitiated.
A 4.0" dia 100 cell cat will deliver an equivalent flow rate of around 72.25mm once cross sectional area has been calculated and laminar flow corrected.
With regard to the road legality it's true that the value lies in the amount of precious metal in the cat washcoat -  a 5 gram washcoat will get a cat through an MOT once maybe twice and then its going to start to struggle due to basic entropy...
In addition the quality of European fuel also has a knock on effect with regard to its long term effectiveness, when compared to say US fuel.
We offer a larger 125mm 200 cell cat which gives a genuine corrected flow ratio of 79.0mm in addition we offer a 40grm washcoat to provide complete road legal conformity with current MOT legislation and to ensure the durability of the cat.
For guys looking for big power we recommend the new 100 cell variant which definitely out performs a cat delete with a corrected flow ratio of 88.0mm and again comes with our massive 40grm pm washcoat.
Again for cars wanting to go beyond 450 bhp we offer a 90.0mm downpipe and our 140.0mm 200 cell Mega Cat - which has a true 90.0mm flow ratio.
Ultimately the 2 questions that need to be asked are what is the diameter of the cat and what is the wight of the PM washcoat, if this cannot be answered then fear the worst.
It maybe true that there are very marginal gains to be offered by opting for a cat delete against one of our 200 cell cats, but there are also other considerations such as the road legality of a cat delete and the consequences of knowingly running one.
One of the ways that we will be further enhancing the performance of our downpipes is by the introduction of the new 'Softflex' on all 76.0mm downpipes from 2018.
The benefit here is that it has a genuine bore of 76.0mm as opposed to the braided 76.0mm flexis which in truth have only a 70.0mm bore.
Our downpipes and cats are not the cheapest but I think you will not find it possible to source a better one by application once you have determined your individual requirements.
Hope this helps 
Nige

76.0mm Downpipe with 200 cell cat




90.0mm Downpipe with 200 cell MEGA cat and 76.0mm Downpipe with 200 cell cat and OEM downpipe for comparison purposes





76.0mm Downpipe with 100 cell cat and softflex

[Manny_ED30]

Thanks Nige.

If I went with the sports cat DP, how can I determine with flexi is best?

[Powervalve Nige]

The braided flex is the the smaller bore - the chainmail soft flex is far more flexible and has the greater through bore...
Cheers
Nige

[pudding]

I use the APR cast downpipe with a GESI sports cat ($500 on it's own if sold separately!) and as Dan says, the cat is a pile of cack.  If hot enough, it just about scrapes through the MOT at the pass limit of 0.1%.   The pair of stock cats show 0.01% for reference.

Still, my local friendly dealer are happy to let it through and have done for 2 tests now.  Lenient test stations is the key to running aftermarket exhausts!

I like the APR because being cast (and therefore much thicker wall thickness), it's very quiet and has a nice tone.  Currently using the stock catback with it, so a good blend of daily refinement and performance.

[shoaybmakda]

sorry to hijack the thread - but i was contemplating a milltek DP with a sports cat as i already have a milltek cat back - is adding a DP going to add any drone? i currently enjoy the sound it makes but wouldn't mind a little more rumble. my car isn't mapped to crazy numbers or i don't use it for track or anything but just slowly adding performance mods to my daily to keep things interesting in my car.