ROG100

That is the Dave Lomas X pipe designed in conjunction with Louie Ott and dyno tested to the extreme and the SS Cat Back exhaust. I have one fitted on my GTS - awesome.

MotorSport SLC make the X pipes and cat back system and they are sold by 928sRus and 928MS.

Red Flash

Dave, thanks for chiming and offering to help. I didn't know that this product was still being made and supported. The point above indeed could be the problem. I have it my mind they are Magnaflows, but I'm not sure. I will update in a short while when I get a chance to look again.

Since I like the sound of the car as it is, the best thing to do is probably to work with you and buy better fitting cats or something to get the fitting issues resolved. I also suspect that the cats might be slightly plugged up. So, buying new ones is an option.

Unfortunately, since I don't have the history on this aspect of the car, I have no clue why it is like it is!

Mark R.

Both of my S4's currently have x-pipes installed.
One is an old original from Louie, and the other is a more recent one from Dave.
The x-pipes look similar, and I assume for the most part, are pretty much equivalent.

My 88 five speed has the small resonators, so I had to reinstall the rear muffler.
It is still pretty loud and roudy sounding, but fine for a weekend fun car.

My 87 auto has the large resonators, so I tried running with the RMB in place.
But it was just a little too loud for a daily driver, so I put the rear muffler back on.
Now, with the large resonators and rear muffler, it is actually a little too tame.
But running with only the two large resonators alone is just not enough...

Just my experience...

P.S. - Catalytic converters (all) definitely add some noise muffling.
Of course, it can vary significantly with the type (size, flow, restriction, etc.).
But they all add some amount of extra suppression...

worf928

Here's a picture of the end of John's x-pipe with cats. This is more-or-less the way it was originally installed (not by me.) As far as I know, the x-pipe and cats were supplied by SLC. It's pretty clear that the cats are too big. Despite what it looks like the exhaust does seal at the cats. The only issue is that R&Ring the RMB is a four-handed job because the ends of the mid-pipes are forced apart because of the cats.

I did advise John that the simple route would be a new SS RMB (the aluminized RMB is showing its age) and a ratchet strap during the install to force the ends of the mid-pipes together sufficiently to get the RMB to seal.

Andre The Giant

Not sure if this has already been done, but it would be nice if people could record the sound of their setup for about 30 seconds or so, idle and revving it up a bit, and describing their exhaust setup so we could actually compare before making this purchase.

I say this because that is on my list of modifications I want to do to get a few more guaranteed HP and a little more sound, I don't want too LOUD since I love to use my car as a daily driver from spring to fall.
I actually have a little clip of my original sound.

Tried uploading a little .MOV file but could not, is it possible or do I have to upload from a web link ?

tv

What that pic above shows is not the way to build a proper custom exhaust imo. My post from the other current exhaust thread;

Stock cats, I believe merge the exhaust flows, much like a crossover, X Y H, would. I have read all the threads, posts, articles I could find years ago about scavenging etc. I don't believe the possible gain in power is worth the lower quality in sound. Some believe that the quickness of the air flow is just as important for power, fewer curves in the piping, not opening into larger diameter, not going into a large muffler.

A true dual exhaust on these cars sounds best and that is custom, but you need 2 cats and 2 "mufflers".

my muffler -- https://rennlist.com/forums/attachme...ystem-muff.jpg here http://www.summitracing.com/parts/mo...WCMhoCyXzw_wcB

my cats --https://rennlist.com/forums/attachments/928-forum/97558d1138578671-anyone-working-on-a-16v-exhaust-system-dynatech-cat.jpg here http://www.summitracing.com/parts/dt...0025/overview/

Everyone's tastes are different, but this setup produced the best sound I have heard so far on a V8.

My system is completely SS and tig welded, 1 piece (but completely dual) from header to tips that can be carried with 1 hand. No leaks, no rusting, no vibrations, no droning. It can be done, other than being a tig welder, I had no lift or special equipment. YMMV look before you leap

bureau13

Is this really true, about the stock cats incorporating a crossover? I've never heard that anywhere else. Not saying you're wrong, just surprised at the gains people are measuring with an x-pipe if the stock system essentially has he same thing, or close.

worf928

Not on 87+.

tv

I said, 'Stock cats, I believe merge the exhaust flows, much like a crossover, X Y H, would. '


I believe I was right, here are the pics of different years;

80-84 US from 928 intl and Porsche - https://rennlist.com/forums/attachme...erters-cat.jpg

85-86 S3 - https://rennlist.com/forums/upload/cats.jpg

87 stock -- http://members.rennlist.com/dan87951/cat3.jpg

another early car version -- http://members.rennlist.com/porken/7...rossmember.jpg

some mystery version -- https://rennlist.com/forums/attachme...s-image014.jpg


The common feature is that they are all merging both banks of exhaust before the cat and even do a rudimentary version of a crossover. It was even discussed here - https://rennlist.com/forums/928-foru...l#post11233572


So I really don't know what the big deal is about XHY pipes, but still say for sound and exhaust gas velocity the setup I ended up with works best that I know of.

worf928

Merged exhaust is not a crossover (as in X-pipe.)

bureau13

Ahhh, I see what you're saying. Looks a little like they put in an "H" crossover thingy right before the cats.

James Bailey

the H thingy mostly gets the oxygen sensor into exhaust gases from both heads....