Header options advice needed
 

Having upgraded the intake/throttle body side and just having had a custom tune done, I’m now considering some exhaust mods. At this point I have stock headers/cats, secondary cat bypass and stock muffler. I’m currently getting a CEL due to bad cats. I tried changing the O2 sensors but my Durametric tels me my cats are operating below spec. So... Do I replace the bad cats with stock? Do I try to find some 200 cell cat/headers? Do I put on catless headers and put my secondary cats back on with new bungs welded on for the O2 sensors? Or what else?
I am not interested in changing the sound. I track this car but I do use it around town so I don’t want to make it much louder. Any wisdom would be much appreciated!:)

I am curious to the responses also, I asked similiar question without much response.

My theory is headers with 200 cell cats, into the cat bypass. Will be a little louder, but will be breathing well, and the stock muffler will keep it toned down. At least in my theory.

Since you increased the input flow, it needs the exit to flow better. But this off my knowledge of 350 V8, but principles should still follow.

Concern would be how much back pressure to keep the bottom end torque nice. I would think stock muffler would work well for that.

Anyway curious to responses too.

Consensus among the cognoscenti is that best power is obtained by cheap Chinese long tube headers with NO cats feeding secondary pipes with hi-flo cats wired up to send the proper OBD signal and then the muffler of your choice.

Interesting. Any links or sources? :)

Negative, Ghostrider.

No cat tubular manifolds and 100 or 200 cell cats, I think you call them mid pipes or rear cats, works well for us in Europe. The cheapy eBay manifolds work fine use them on 2 Boxsters since 2012.

The only 200 cell secondarycats that I see on e-bay are the Circuit Werks brand at around $400 or so. Are you referring to these?

Out of curiosity, why do the long tube no cats with cats in secondary, produce more power than, short 200 cell cats, with no secondary? Generally same set up, with cats in a different position. Must be the design of the longer tubes.

The UK has exhaust test for inspection, that setup still passses?

I recently did my exhaust. I used eBay headers and eBay secondary cat deletes and stock muffler. I can tell you that it is really quite while cruising and accelerating but can get a little loud at wide open throttle at times. Not obnoxious at all and sounds really good. I also installed them at first using an O2 spacer and that didn’t set off my CEL at all and my emissions were ready except the SAI system. I was clearing codes almost weekly as my SAI was throwing codes but nothing else.

If you can go back to the dealership and convince them to put on a row tune, it’ll solve some issues unless they do emissions check where you’re at.

Circuit Werks isn't a known name here so it's not these. Search eBay UK for a comparison. There are a couple of retailers here that sell the mid/secondary pipe with cat. My old ones with 100 cell cats eventually failed the emissions so I have reverted back to the standard ones until I get a new car core welded back in.

If the straight mid pipes are cheap enough there's no reason why you couldn't modify those to insert a cat and copy the shape of the ones with the cat already in.

The exhaust is one of the places the Porsche used to keep the 986S down on power and out of the 996 market share. If you compare the two cars' exhausts and consider how much more power the 3.4 makes over the 3.2 it starts to become obvious. Anyhow, better headers are step 1. I've had the Chinese headers on my car for over 10 years now and they worked great. Were I to do it again, I'd go with the larger tube 987 Chinese headers which are only slight more $$. I've got the Fabspeed secondary pipes with 100 cell cats welded in. The advantage over stock is the larger diameter along with the much less restrictive cats. Originally I had the pipes without cats coupled to a Borla muffler. The SCCA judges started hassling me about the car being over their dB level so that's why I added the cats. After a few years the Borla fell apart so I had single chamber 2.5" Flowmaster mufflers welded in place, maintaining the 2.5" diameter throughout the system. Sound is good, power is 244 at the rear wheels.
From what I understand, the stock muffler actually flows pretty well despite the small pipe diameter. As well,it's got the acoustic tuning to eliminate drone. Probably the biggest advantage to dumping the stock muffler is the weight loss.
Hope this gives you some ideas to consider.

The circuit werks are made by a company in Texas, I just received my secondary cat delete pipes from them. Visual they look well built, price was right, and they shipped within 2 hours of me ordering them. Not sure when they will get installed to do review, probably fall. I want to get an fvd sound version put in same time, plenum throttle, and the fvd tune. So spreading the purchases out several months.

Anyway the user reviews i have read on the circuit werks have been positive, so hope they work well.

Fluid dynamics....
 

...the critical part of exhaust flow is immediately upon exiting the exhaust valve. Long tube headers with no cats allows the exhaust to QUICKLY get outta the combustion chamber and if tuned properly helps “scavenging” that allows intake flow to be better in addition to exhaust flow.

The exhaust gas cools very quickly and slows down as it cools due to the laws of thermodynamics. This is why cats that are further downstream don’t have as big a detrimental affect on exhaust flow.

The stock muffler actually works really well and the car NEEDS either the original muffler or a high quality copy of similar shape and mass because the entire drivetrain WITH the muffler was balanced and tuned by Porsche to act as a mass balancer of sorts for the entire vehicle. Only a big single can will prevent the horrible drone on the highway in top gear.

The FVD Brombacher “Sound Version” muffler is very expensive, but it is built out of T316 stainless, a much higher quality of steel then even the OEM muffler, provides a great sound, will stay shiny for life, and will never burn out. That is the best option for a real world, street driven car.

If you don’t care about cross-country driving without a headache, then buy any muffler you want.

The high flow cats in a quality secondary pipe won’t affect your power output much. For a street car, you really should run them if you use long tube, catless, headers.

The factory header with the cat built in is that close to the engine for a reason. The factory needs the catalyst to get “lit off” as fast as possible to pass the government smog tests. The cats need heat to work, and sticking them in the pipe as close to the engine as possible let’s them pass the smog test, because that factory test has a cold start portion and the cats have to get hot as fast as possible to pass.

For us out in the real world, where we drive to a smog check station, having the cats eliminated from the headers and just mounted in the mid pipe downstream doesn’t hurt us, because the car is warm and the cats are hot by the time we get to a smog check station and they can scrub the exhaust clean.

It’s just science.

Thanks for the run down, already kinda had an idea on the long tubes after thinking over it. But learned something new on the cat placement and why.

Welding a pair of high flow cats into myTopspeed bypass tubes is probably a viable option. I guess I would need fore and aft bungs to accommodate the O2 sensors as well as longer wires for those. Should I forsee any problems with CELs popping up?

Ebay has a plethura of headers from $125 to $1200 listed.

Look at the catalogues for what you call ROW. These are standards parts in Europe. On 986 we only have the rear cats. Early cars only had one set of lambda sensors and later cars and both before and after.

and consider the 987 oem muffler with cats built-in as well (if you want to keep cats at all).

Assuming that yours is a USA-spec car, suffice to say here that getting a ROW tune opens up a very large number of potential exhaust options for you. Any one of which will be leagues above the restrictive OEM cats within the stock manifolds.

I am only about a month away now from wrapping up a top-to-bottom review and rework of my exhaust system. I'll end up with what I personally feel to be the "right" system for me and my usage of the car.

My intent is to start a new "What I Did" thread here once completed. But here's a sneak preview picture.

Thanks - DM

http://986forum.com/forums/uploads02...1529680880.jpg

now that your tech knows how to push a tune onto a car, it is quick work to get a row version of your current flash (5 minutes). if allowed by law, of course (not sure what's up in pq). worst case, register it in the nwt - i just put plates on a full race car from 1968 up here - no inspection, nothing (no horn, no, turn signals, full cage ...).