I'm thinking of getting cats for my C2S but don't know which number of cells should I go with and which one going to give me power the most. Is it true that it causes some Loss low end torque at acceleration but gains on upper end. Is that true

Right now I have PSE and x-51 headers and I need your help to decide.(bypass cats, 100, 200 or 300 cell).

 

I would go with 200 so that way your car does not throw any CEL codes.

 

100/200/300 cell cats with the PSE will be VERY VERY LOUD INDEED! The standard cats on a 997S do half the silencing, the mufflers the other half. 200-cell cats plus the non-PSE, standard exhaust cans is a very loud combination as half the silencing has gone (guess what my car is running at the moment)! With cats + PSE in open mode, 2/3rds has gone compared to a stock car.

Unless you want a car that screams 'look at me' (and why not ) then you should listen to these combinations before you buy. For the most part, a muffler designed to work with the standard cats will be unusably loud with free-flow cats. A muffler such as AWE is designed to work with free-flow cats and is more controlled. Conversely, a muffler designed for use with free-flow cats will usually be no louder than stock if used with standard cats.

Ian

 

I am going to install my PSE muffler with my AWE Cats and my Evo Headers, and intake. I have done dB readings before and I will do them after the change over. I have been told that 75% of the sound comes from the mufflers and that it only gives you about 10% of the gains. I am curious as to how much the system will really change the sound and gains. I am of course hoping to tone it down to a civilized tone.

I will report my findings either late tomorrow, or Friday.

 

Yeah why not "look at me" I want my car to be loud but I'm asuming 200 cell with PSE woudn't be louder than bypass muffler pipes rght?

 

100 cell I think you might need to have the ecu tuned, however on the safe side stick to 200 cells and dont look back.

 

More important than cell count is the manufacturer of the cats.

For years, the best cat we could find was a US produced metal core 300 cell unit. However, cat technology around the world has improved, and now the clear leader are the Emitec cores used by HJS.

Emitec is an OEM German supplier to VW/Audi/Porsche, etc. HJS gets cores made to their size specs from Emitec and "cans" them in heavy duty stainless steel housings, readiy to be installed in aftermarket exhaust systems.

The genuine HJS cat in a 200 cell configuration is the only cat that we have found that works on all the modern Porsches, as well as LEV, ULEV, and SLEV cars that we also produce exhaust systems for.

There are very few companies that are using real HJS cats. Beware when someone tells you they are using a German cat that is not HJS. We have searched high and low and the only real aftermarket German cats are from HJS, and the can will have their part numbers and name stamped on it. Seems that all European aftermarket exhaust manufacturers and us here in the States are the only ones using HJS on all their systems. I have heard rumors that B&B has started to use them, too, but cannot confirm.

HJS cats are over $400 ea as a landed cost here in the States, which is why most US exhaust manufacturers are hesitant to use them. We get them by the pallet-full, which ties up almost 6 figures worth of dollars as they sit in raw form in inventory waiting to be installed in our exhausts, but there is no substitute.

So bottom line, if it is not an HJS cat, step away quickly.

If it is an HJS cat, we have found that 200 cell count is the most stable for long term CEL avoidance on US spec cars. 100 cell can work sometimes, but the power advantage over 200 cell is very slim and the threshold for keeping the CEL light off is much smaller with the 100 cell.

Hope that helps.

 

Todd,
When Did you start using HJS?
Can we upgrade old awe cats to new ones if were getting cel's?
Regards
Simon

 

We started using them about 2 years ago.

We have a discounted price for original owners of our old style cats that would like to get the HJS ones under warranty. PM sent.

 

Todd, Can you address the question of sound with the 200 cell cats and otherwise stock exhaust? It has been said that AWE "cats only" is a louder system than AWE cats AND cans. True?

What about power curve? Is there a loss of low end grunt in exchange for mid or high end power? I am very close to pulling the trigger on a new system (AWE is at the top of my list) but hear so many conflicting stories it makes me hesitant to spend a chunk of $$ on what could be a mistake.

You are the proverbial "horse's mouth". Give us the straight scoop. Thanks.

 

Um, err....

I'll be completely honest here. I don't think I've ever heard our cats when used with otherwise stock parts. During development, we tested many combos, but not the cats alone with stock mufflers and headers. We've probably had that combo come through the shop at some time, but I can't recall what it sounded like. My experience in exhaust development leads me to believe that our mufflers coupled with our cats would be louder than OEM non-PSE mufflers coupled with our cats.

Check out our site for LOTS of dyno results:

http://awe-tuning.com/pages/info/con...cfm?content=38

The tuning of the 997 exhaust is not so delicate as with other cars (like the 997 GT3), so I would be very surprised if there was any loss of power using our cats with the stock mufflers vs with our mufflers.

Sorry for not being a better horse, here.

 

Todd, I have your cats with a set of Evo Headers and Stock PSE mufflers (switched from Evo mufflers 03.06.2008) and the sound in normal mode is very quite (when compared to the full aftermarket system) but sport mode is almost as loud (but different sounding). I have not noticed any change in performance, but my butt dyno is not a good measuring tool, but the sound is the issue that I need to solve. I will be testing the dB levels later today on my car to see what kind of a reduction that the mufflers made.

I am certain that the AWE cats made a huge difference to the performance as I ran only the Evo gear with stock cats, and if I needed to pull the cats then I would just pull the whole system (and go back to full stock) as I felt the cats were the biggest impact on performance. I am happy to say that I can run the current system and get close to achieving the best of both worlds. I am going to dyno my car soon, and I will be comparing my setup with a friend that has a stock 06 C2S as a bench mark for the mods that I have. We are also discussing installing Plenums in our cars and retesting them to see what we gains can be made.

 

Thanks for the info Todd. As you and your development staff know, proper sizing does make a real difference. I have the Europipe system on my 997 TT - it has Emitec 100 cell cats and I've never had an issue with CEL's - no special tuning either. Europipe explained the reason for no CEL's is that the contact area of the 100 cpsi cats they use is identical to the contact area of the 600 cpsi stock cats.

 

Well, I'll admit that the Europipe approach is unique, using the very large diameter cats. I do realize that their theory is that the more cat matrix face you can expose to the exhaust gasses, the more resultant catalytic action you get, but aerodynamic study suggests the problem is more complex than that.

Approach angle of the exhaust gasses as dictated by the inlet cone of the cat plays a big part in how effectively the gasses are "spread across" the face of the matrix. Too shallow of an angle (short inlet cone), and you'll get turbulent and ineffective flow at the far outside area of the exposed matrix. When you look at the Epipe cats, you see quite the transition from inlet tube OD to cat OD happening in a very short distance, which is recipe for fringe turbulence, which in turn negates the potential advantages of the larger core. This is ultimately a packaging issue with the car that the exhaust is being designed for.

Anyway, we have tested many cat configurations, and in reality the difference between a 100 cell and 200 cell cat in terms of backpressure and unleashed power is quite small and arguably within the background noise of a dyno and meter test. Given that the 997TT is starting with an 800 cell two stage cat, we felt it was prudent to leave a bit of headroom on the table in order to increase our chances in long term success of no CEL.

So far, so good.

 

Hi Todd

I'm very interested in some of the exhaust theory you've been explaining in this thread - you are clearly very knowledgeable on your subject.

On my 997S, I'm currently using your cats (very noticeable power increase) with the standard mufflers and headers. I will be adding your mufflers shortly for a better sound. If you don't mind, I have some questions for you regarding your headers for the 997S.

I'm currently hesitant to go down the route of adding your headers as they lose mid-range torque. I would also add that I tried another tuner's 'equal-length' headers (borrowed from a friend who was selling them). They also reduced mid-range torque very noticeably (and my friend now has them for sale again)!

I only use my car on the street and therefore rarely use the engine over 5000rpm where your headers show an improvement. So for me, they would be a downgrade for all practical purposes. I'm interested to know what the criteria were that led to the header design you sell and also interested to know if there are alternative header designs that would equal/better the top-end of the standard header but INCREASE mid-range. Or is it just the nature of ANY equal-length header on this engine that they lose mid range? The standard header looks really horrible (it must surely be very restrictive and does not appear to have been designed with any regard to inertia or pressure pulse tuning). Surely it can't be impossible to design a header that will give increases across the board compared to this item, rather than just over 5000 rpm?

I will be extremely interested in your insights and would also like to ask if you'd consider manufacturing a torque-enhancing 'street' header as an alternative to what is really a 'track-day' header that you currently sell? Assuming such a design is possible, it would be a more relevant part for the majority of us.

Edit: Lastly, it also occurs to me that the mid-range losses might not just be down to header design, but possibly to headers giving rise to different ignition timing requirements. This could leave the standard maps effectively timing the engine wrongly at certain rpms. Have you considered having someone do custom mapping designed to work specifically with your exhaust systems (as many of the European tuners do)?

Regards

Ian