Ok.

I have read that the 997s has a lot of breathing problems and my next set of mods will be to attack this.

Has anyone tried FABSPEED CATBYPASS PIPES?

If so was there a power increase?

Eventually i will be doing:

Custom Headers
Cat Bypass
Custom Sport Mufflers


I hope this will give me the most HP & TQ gains!

 

Mo will this stay a street car as well? If it will you are guaranteed a fix it ticket for noise pollution. Also, the difference in 200cpi metallic cats and no cats is probably only a couple of hp.

Dave

 

Dave,

Are the catbypass louder than the muffler bypass?

I had the muffler bypass on before, but i though that the catbypass would not be as loud as the mufflers will still deaden sound.

No sure, thats just my thought.

 

Cat By-Pass in So Cal???? No way you will get away with that.

In order to do Cat By Pass you will also need to visit your Porsche shop and have them turn off the CEL.

When you start to do these engine breathing mods you will need a custom ECU program (ie Softronics) to really notice and take advantage of the free breathing from intake and exhaust mods.

 

Well when you consider that the cats themselves (OEM) are half of the sound control you will see that this combo will be extremely loud especially with sport mufflers. I heard a 997S with the cat bypass with OEM mufflers and to be honest the car sounded like ****. I do realize that you save alot of money if you go this route instead of buying high flow cats but an alternative would be to go with the FVD route. You can buy 100cpi metallic cats by themselves and just build a cutsom cat pipe and either through software or 02 extensions http://shop.fvd.de/us/en/Porsche-0/9...Extension.html



you can avoid the dreaded CEL..


Dave

 

NA motor needs some backpressure to operate efficiently IIRC, whichever changes you make be sure to dyno before / after to make sure you're going in the right direction. My humble opinion is to not mess with the cats, if you remove them the car will be very very loud. I've tried several different configurations and my best netted gains / sound so far have been with the combination of:
KN intake
Stock cats
AH mufflers
IPD plenum

Car is perky and quick as heck, and my gains were verified on the dyno throughout the upgrade process to eliminate guessing. I have not done software yet, still undecided on which one to get.
The lead tech at Pacific Porsche had my car in the other week and was asking me what mods I had done to it because it felt so much faster / quicker than a stock 997 - plus he thought the exhaust sound was stellar. .

hope that helps.

 

go high flow cats, do the environment a bit of a favor and keep a bit of backpressure also. socal with its street mounted sniffer operations from time to time could prove expensive otherwise...that ticket is not cheap.

 

Yes and no. NA motors don't "need" the back pressure, it's really about where you want maximum power. Ultimately you want an efficient "pump", where air can get in and get out.

That being said, at 7k rpms the ideal exhaust is very different then the one at 2k rpms Slower exhaust flow means it can cool quicker and become more dense, so a fully open system may actually decrease velocity which would seem counterintuitive. However that same exhaust at 7k rpms may not have the density change issue, so it's a benefit instead of an impedence.

Take header design in racecars, the headers on a NASCAR V8 look different to those on a Formula1 V8, because one is designed to operate at around 8500rpm and the other at 18500rpm. Either way though, neither is concerned with how much torque they have at 2k rpm and what advantages they could have by redesigning the exhaust to maximize power at 2k rpm.

So NA cars don't need back pressure, what they need is an exhaust that maximizes velocity (and scavenging) at the desired operating rpm (or range). The issue is designing something optimal that covers 6k rpms of use. Like the concept of variable intake manifold runners (or in modern times variable trumpet heights) that switch from long to short at varying rpm/throttle, the aim is to have it both ways. Though unlike intake manifolds, changing exhaust diameter (or flow restrictions) based on RPM sounds like a difficult thing to manufacture and implement. The best I can think of is like the PSE bypass design, but imagine that linked to RPM so you can remove restriction as RPMs increase. This would be difficult for the daily driver though as the exhaust would change in sound as they drove, which would likely be a complaint.

Given modern ECUs which are counting on the O2 delta from pre to post catalytic converter, I say running no cat's is giving up too much. I'd go high flow if you want, or stay stock. You keep the ECU happy, no issues with SMOG, etc. Bear in mind, cars run extra rich on cold start to heat up the cat's as quick as they can to get them working, imagine where all that fuel goes without the cat's? I think to run correctly without cat's you need an ECU re-tune.

 

Ryans4- Good post / info. I was being very general with my backpressure comment so forgive my "layman" terms. Not being a tech myself, all I can really speak on is from my experience. I noticed that keeping some backpressure in the system resulted in better TQ across the band, whereas opening up the exhaust (trying muffler bypass with stock cats, then trying stock mufflers with cat bypass) resulted in lower TQ. This could be due to the stock ECU software mapping correct? I had similar results on my 996.

most of my driving is in the 3-6k range, and the AH pipes combined with stock cats + intake + IPD have given me the best results so far with increases to wheel HP/TQ in this range. Maybe it is the nature of the muffler design giving some backpressure at lower RPM and then being increasingly less restrictive as RPM's increase? I don't know the science behind it, all I know is it seems to work pretty well so far. Do you think adding a custom tune to the ECU would help out even more?

 

No worries at all, I wasn't calling you out or anything. Though I'm really curious to see back to back dyno runs on the same car with various exhaust configurations. Not so much for Torque but I'd like to see how the peak HP changed. Can you post pics of your various dyno runs?

As for the ECU Tune, having someone sit down and work out the best setup for your parts/environment/gas is great. Think of it this way, Porsche has one ECU that all of North America gets, from the poor people in Las Vegas at 2500 ft above sea level on 91 octane fuel with ambient temps in the 110F's to the lucky ones at sea level on 94 octane running around on 50F days. The ECU has to do a lot manage that variation in conditions. The ECU is smart though, it can advance and retard timing to make up for good or bad fuel and what not, but I can only assume the range at which the car can adapt is fixed. And they presumably build that with the factory parts in mind. So say you can reprogram the car to not worry about 91 octane fuel, or higher altitudes, etc. And you can push that timing range up to take advantage of performance parts on the car. A lot of this is speculation, but I have to assume there is a fixed range to what the factory ECU can adapt to.

 

No worries brother- I have been trying hard to openly document the process.

Dyno charts:
After installing AH pipes and comparing to stock :
https://www.6speedonline.com/forums/...ds-coming.html

Dyno charts:
After installing IPD and test results with stock mufflers / AH mufflers:
https://www.6speedonline.com/forums/...o-results.html

A Dynapck dyno was used to do all tests, the run actually starts on the graph at the valley of the first dip (when clutch is dropped in 3rd-gear roll on). Nature of that particular dyno I guess. Not so concerned with peak numbers, just the gain changes shown between initial baseline runs and post-modification runs.

I didn't keep the run charts from the muffler bypass pipes or cat bypass (stupid!) the avg. loss IIRC was about 5TQ in the lower to midrange, HP was fairly unchanged. Plus the car was TOO LOUD!

I have a dyno run chart from my 02 996 with stock cats, KN intake and Agency mufflers posted SOMEWHERE here in he 996 forum, but I can't seem to find the thread (from 2 years ago). IIRC, Adding the Agency mufflers and KN intake netted me about 7HP / 8TQ gain over stock mufflers / intake. A very good mild upgrade.

 

I have to say that I have been greatly impressed with the sound of the AH mufflers. They sound more "gurgley" than other variants, almost like a mid point between a muffler bypass and a Fabspeed muffler. I've been a Fabspeed guy, but I think it's time to try a set of these. I won't mind the weight savings, either.

 

Cattman- I think you just described the sound about perfect as I have heard both (bypass and fabspeed mufflers). Well put

..thinking about it, that statement really makes sense. They are pretty much just elongated straight-through bypass pipes with a couple of tuned resonant sections- One could call them a "muffler / bypass pipe" hybrid I guess?

 

I have both Fabspeed cat bypass and sport cats. I bought the sport cats cause of noise restrictions at certain tracks. The car is stronger with the cats in.

 

I tried a few combinations and found the following to be the best balance:
1. Softronic software.
2. OEM mufflers.
3. AWE 200 cell cats - no CEL issues.
4. Porsche X51 headers.

You get increased performance, remain street legal, don't end up with Check Engine Lights, save your wallet, etc. The X51 is a pretty good solution for only $625, the AWE Cats are fantastic, and the combination of it all gives you a great sound to boot.