OMG true pro fabrication

 

We plan on making the entire system modular so that the side mufflers and center muffler can both be deleted together or separately. I am not sure we will see much gains from a "freer flowing" center muffler. As it stands, it is a straight through design, unlike the side mufflers which are baffled.


Each bank of cylinders passes through the center muffler via a tight u-bend on each side, with a few inches of perforation exposed to the can's shared interior volume, which acts as a sound cross over.


Hopefully by end of December, if not sooner. We are able to re-use a lot of existing components, such as can skins, collectors, cats, etc. The rest is just making bends on our bender, cutting and welding, and then polishing. Our bypass parts will probably be ready much sooner.

I am not keen on building a header with a close coupled cat (meaning having the cat very close to the exhaust ports). The HJS cats are a metal core, and they do not fare well when exposed to the high EGTs found there. We opted not to do Cayman headers for the same reason, and to date most companies making Cayman headers with aftermarket cats in the stock location are having failures.

If there were a high quality high flow ceramic cat out there, it would be able to withstand the heat and pounding of a close coupled location. To date, OEMs are the only ones having close coupled ceramic success, but they are not high flow.

 

Our cats will be repositioned. See the response above why we do not want to place an aftermarket metal cat in the stock location.

Depends on what you refer to as the primary muffler.

I would not call the center muffler the primary muffler in terms of sound muffling. It may be the first in line as the exhaust gasses make their way to the tailpipes, but my guess is that its job is mainly to address some rpm/load specific harmonics that cropped up when moving the cats closer to the cylinder heads. Unlike on a 997 GT3 or GT2, this center muffler is playing a secondary position in sound muffling.

The side mufflers are doing the majority of the work, and they appear to be the same type of baffled design like on the previous gen 997.

Ultimately, we will do incremental power and sound level/load testing on the various bypass parts we are making, which will quantify what you get at each stage.

 

Thanks for the reply, Todd. I am saving my Christmas money!

 

Todd,

If the side mufflers are similar to design to the previous side mufflers, can we assume then that the center muffler is purely there to adjust the harmonics of the total system. If that is the case, then why are the harmonics different than the previous model. Is the reason because of the placement of the cats, design of the headers and the overall length/travel of piping. Just trying to understand the reasoning behind Porsche's design change.

Finally, I have seen another design where the cats are connected to the headers as one piece (similar to the GT3). If the exhaust path remains the same by going through the center muffler, then the side (improved) mufflers, then out the tips, wouldn't this eliminate the concern of dispersing the heat?

Thanks.

 

In my opinion, the harmonics probably changed due to moving the cat closer to the exhaust ports. This is the trend for a lot of OEMs as they seek to improve cold running emissions. By moving the cats closer to the exhaust ports, they "light off" faster, beginning their catalytic action sooner.


I am unsure what you are stating here.

Are you asking that if EGTs at the cats remain the same even if they are moved away from the cylinder heads while keeping the center muffler and side mufflers n place?

Increasing the distance alone from exhaust port to cat placement will drop the EGTs that the cat sees, regardless of what remains in place after the cats.

If I read that question wrong, let me know.

 

So that is the goal for keeping EGT low: moving the cats further away from the heads. Why can't someone use Porsche's design for their cats, (which is right off the heads) yet convert to a free flow design.

Thanks for your explanations.

 

Well, there are still benefits to moving the cats away from the heads on this engine. Unless the cats are moved away, it would be incredibly difficult to improve the header flow without seriously compromising road clearance.

That is why the header tubes are so "squooshed" looking on the OEM headers. They need to snake from the head to the cat in a short distance while allowing access to their fasteners and also providing road clearance.

 

I would say that the length of the exhaust pipes are different that the older model and the harmonics of the sound changed. I have seen 2 video's on the net:
1- the center muffler is removed on the 997.2 car and stock side mufflers remain and the car sounds better to my ears but is louder than a stock 997.1

2- the side mufflers are removed and the center muffler remains and to my ears this sounded the best per the video. In person the sound will change so who knows.

I was thinking that by removing the side mufflers you lose a lot of rear end weight and then use a center free flowing muffler with out the U bends could be used. Elminate the U bends and have for example the right side exhaust exit through the left tips and vica versa. This would be a more straight flowing design.

 

Here's a silly question, Todd: Why not use the old 997 exhaust system and bypass the center muffler with long cats like before.

 

It's a new engine and Porsche redesigned the exhaust to cope with the changes, don't forget there is DFI too.

 

mdrums, can you please post links to the videos. thank you

 

seven, understood, but that doesn't conclusively mean you can't have the exhaust in the same format as before especially since the design of the headers and cats on the new model is even more restrictive than before.

 

That's a really good post, a company who show all it's R&D, how it works, is a company who is proud of his work, a company that customers trust !

 

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