Suggestions re Conservative Upgrade to Factory Exhaust System - 89 911 Cab....

[ajmarton]

I already have a SW chip and wouldn't mind squeezing a little more HP out of my 89 911 cab. A lot of the threads I found involve radical (to me) modifications to the headers, cat and muffler system. Is there a middle ground or should I just go with a stock Dansk OEM replacement? I live in Califorrnia and the 911 has to pass an emissions test every 2 years. I would like to upgrade the exhaust and whatever else but keep the basic functionality of the heaters and no major mods. Any suggestions?

[RWebb]

find a high flow cat to replace yours with that CARB certifies

some manfs. have used dual cats - may be system like that also

[Zeke]

I replied to this earlier and hit the wrong button. Just pissed me off.

What I said was that I have read all the exhaust threads about 3.2's. My learned opinion is that the performance gain is to relieve the constipation before the cat, not after. Or do as Randy says.. Unless you are willing to ditch the cross over HE's, a muffler swap won't gain much except a different sound. You may feel you're going faster if it's louder, but the HP gain is marginal.

There was more to my original rely and if you want to hear it, ask.

[ajmarton]

Thanks Milt. I would love to get your full commentary.

[bmgmd]

I use early HE and 2-in-1-out OEM muffler, SW chip to match.
I swap the exhaust every 2 years for smog check, then usually swap back to the early HE set-up. Throttle response is probably the best I can get on a stock engine.

The SW chip is new since the last smog; I will leave it in and use the stock exhaust to smog this month. Hope it passes.

Brian

[Zeke]

Originally Posted by ajmarton

Thanks Milt. I would love to get your full commentary.

Well, it's sorta covered already. The early HE's or SSI's is one way to get some backpressure relief. I also mentioned (or tried to) the dual cat proposition. Keep your eyes out for a custom system by M & K for mmasotto on this BBS. It's not finished yet.

[911st]

The stock heat exchangers are not as bad as some like to think. The numbers I saw is SSI's have a 5 -7 hp advantage at 3000 and 3500, after that they are dead equal.

Dropping the cat and adding a sport muffler is good for 11 to 16hp from 4000 to 6000rpm's.

The SSI's may be felt more on daily driving but the stock headers w cat delete and sport.

It is possable that the SW chip may have already gotten you part of the HP gain availabe form the exaust change.

Please check you A/F's on a dyno, even if the chip is made for your combo. Mine was to lean.

[RWebb]

I agree completely with milt's comment - BUT I do not know of one that is smog-certified. The old-timey header type design is clearly better than the stock 3.2L setup re hp. That keeps SSI in business...

[WI wide body]

I don't mean to hijack this thread but you guys made me think of something:

I don't really like the way my muffler hangs down. See attached pic.

I was thinking of replacing it with a smaller (narrower) muffler and maybe also getting rid of the cat at the same time.

Got a couple questions...what happens to the O2 sensor? Or, what's the best way to to replace what the O2 is supposed to do if the cat is eliminated?

Thx.

[911st]

Most cat bypass pipes have provission for the O2.

Why not use a mirrored factory muffler with a second tail pipe. It is dyno proven design that works. There is a little to be gained over this without way more noise and drone.

---

SSI's and pre 75 exaust is on the size small for a 3.2 Carrera motor for it to achive it's full HP potental.

SSI's are great and make a Carrera more drivable and do add HP around 3000 to 3500rpms.

Per the dyno comparison I saw, they do not seem to add any HP after 3500rpm over a factory set of heat exchangers if the restriction of the cat and muffler is addressed.

SSI's are a pice of art, make nice music.

Opertunity may be to find a high performance cat to replace the factory cat. If there is CARB aproved cat that would be nice. If there is would be interested myself but not if it is $500.

One could use a cat bypass pipe as a bassis for constructing a performance cat system that would work and should pass smog.

However, I suspect a better soluition would be to use the factory Cat can as a base as it has a nicer connection fit and may flow better when done.

I started to try to look into high flow cats but did not find any clear winner. Random Technology was one that migh offer potental. I am not sure what a 100cell race cat is but could not find a source for one in the US.

The right highflow cat with a sport muffler has the potental to achive close to the same HP in the 4k+ range as any SSI based system. Again, because of it's larger primary tube size over the small 1.5 inch SSI system.

I would love to see a long tube 1.75 equal length header system where the three primary tubes are stacked and the collector stays open to the cat. Then it could have a B&B or flowmaster style muffler. It would be expensive...

The Pete Webber design headers could be a bassis for a long tube header design that could leave room for the cats before a muffler.

GHL makes a Header w cat system but it is a very short tube design and I dought it would be any better than somthing based on the stock HE's.