De Cat of standard header

Has anyone tried de catting the standard header and have any experience on the result both in terms of sound and Hp Gain (if any). Thanks

Good question! Also would de-catting the headers set off the O2 sensor?

The primary cats are located in the manifolds to ensure a quick warm up and compliance with EU class 4 emissions as quickly as possible. Their size by comparison to the secondary cats is much smaller and when the secondaries are warmed up , these are more than capable of the lions share of the work. The second set of Lambda sensors in the headers downstream of the primary cats need to be disabled via the ECU to prevent emissions warning lights. However , the engine control is determined by the primary lambda probes upstream of the cats so there should be no ill effects other than an error message on the dash. Having heard de cat pipes and 100 /200 cell headers on other cars I'm interested how the standard headers with the void from removed cats will sound , and if a gain or loss in Hp and torque will result from them being removed. For interest the 2.7 987 (pre 2007 with M96.25 engine ) has 400 cell ceramic cats as standard in the headers.

Berty, I have not done this on 987, but on other cars i have done this on I gained about 5% gas mileage and a bit more low end torque.

I have catless exhaust set up. Before and after install are very different. Mid range to top end power feel way better, also response better. But it's gonna be really loud though.

Thanks for the feedback. I am hopeful that by keeping the rear silencers stock (keep the rear cats and silencers untouched) the sound increase will still be manageable. I have the factory PSE fitted and this is way quieter than standard with the valves closed. If I can achieve a good sound and power gain with the PSE in quiet mode and something louder but still tolerable with them open , I will be pleased with the result. I will post something up on the articles section if it proves to be successful , along with sound clips and dyno runs.

I run the NHP catless race headers with the stock silencers (not the Porsche sport exhaust). The exhaust tone is a bit deeper, more open, and throaty, but it still retains the classic flat-6 stock Porsche sound, just a bit louder. Sorry I do not have sound clips or dyno runs. I really like the change in the exhaust note and would not change back. In swapping to these headers, I did not notice any loss of low end torque, but the pull in the middle and upper rpm ranges is noticeably more stout. If you look in the dyno section of the forum, you will find evidence from Tomaz that paints a nice picture for this modification.

I am very interested in your setup because I want to do the same. I know that carnewall replaces the cats in the original headers with a new ones with 100 or 200 cell. I think than 100 cells could be a good option because you don't need to reprogram the ECU.

I saw that you have de ECU Flash from FVD. Can this software prevent the ECU warnings?

softronic I believe does the same. I originally planned on getting catless headers, there aren't any emissions tests here in Arkansas, but since I plan on moving to Georgia, catted headers are in my future.

Bought the CEL adapters from maxspeed motorsports and plan to fit these with stock headers that have been de catted without modding the ECU. The idea behind the maxspeed solution is that a mini cat is part of the adapter so the second lambda sees the correct oxygen value and therefore doesnt throw a fault. It will be interesting to see the results and how the longer fitting sits in the space confines under the car. Regarding the ECU reflash Rhonda, do you have a graphical comparison of stock versus modified Bhp and torque for a 3.2 S 987 ? My car appears to have a development porsche map and i have a plot of this before any other mods were carried out. The flywheel hp was just over 291 Hp versus stock of 280. The power and torque curve is also significantly more agressive compared to standard once the resonance flaps modulate around 3000 rpm.

If you're talking about gutting the OEM headers, it's not a great idea. Some have experienced a loss of power due to improper back pressure. The aftermarket headers are designed to give proper back pressure.

It's improper flow momentum -- not improper back pressure -- that kills the power. So with the stock headers, why not just cut out the section with the cat and weld in a 1.5" or 1.75" pipe (I forget the OD)? That would keep the exhaust velocity up while removing the restriction posed by the cats. If you can weld and don't mind more noise, you can't go wrong because pretty much any angle of pipe (i.e. no mandrel bend) is going to flow much better than the cats were flowing.

Im trying to do this the simplest way , so dont really want to get into making a jig (for re welding) and cutting out the original cat housings. I understand that the void created by removing the cats may potentially increase turbulence and create a drop in gas velocity and that bridging the void with a straight pipe would be better. I will look at whats involved in doing this and if its possible to weld that far into the manifold tubeing without cutting off the ends of the manifold. Catless manifolds are on offer for around 500 pounds or 200 cell units for about 600 , re catting the standard manifolds (headers) works out about the same. The used manifolds I have de catted cost 100 pounds , so this is really just an experiment. I quite like the idea of a louder exhaust , particularly as I have a PSE which is far too quiet on standard mode and not enough crackle on bypass. If this works and gives a gain and better sound then I will be happy, if not , I will sell on the manifolds to those that want to re cat with 100 or 200 cell performance options.

Hey all. i am also considering this, but removing the rear cats with a straight pipe from SuperSprint, but keeping the rear mufflers etc, so in essense just removing the two rear cats. i appreciate this will destroy the connection into the rear mufflers, but i have my hands on a second hand muffler, so can return it back to stock if i need to sell the car of get bored with the sound!

Just back from the dyno having fitted the 2.7 catless headers .....some interesting results. 1. The exhaust note sounds richer but without any noticebale drone 2. With PSE "active" the note is much deeper and more raspy, sounds great ! 3. The 2.7 headers fit straight on to the 3.2 S suggesting the reverse is also true. 4. Both the 3.2 S and 2.7 use 400 cell ceramic cats , the difference is the 3.2S uses a 3 into one equal length pipework arrangement. 5. The results show an approximate 5hp peak gain with 1- 2 hp elsewhere throughout the rev range. 6. Most significant is the power no longer drops off so sharply after 6000 rpm 7. Slight loss in torque throughout the rev range , probably due to the headers not being equal length primaries. 8. CEL adapters worked a treat. In summary , I think de catted 3.2 headers will give more power and either sustain or improve torque . This follows the results seen on other cars by the dyno operators when standard cats have been removed. This also shows the 3.2S equal length headers genuinely improve torque over the standard branch design . The M97 engine (2.7 and 3.4) and 2.7 M96 standard manifolds are therefore far from optimised.

I just done this mod and posted it on the forum!!! Its super easy!

you're replying to a thread from 2011, i doubt any of those guys are still even on this forum