ChrisI

I'm running a Dansk Cat Bypass with a cup pipe, combined with a SW Chip. You can definitely hear a difference at startup/idle and under acceleration but if you're just cruising it's really not much more noticeable. I just had a cop doing an on-ramp seatbelt check tell me to slow down because I was going too fast (I was under the speed limit) so I'm sure that was just his way of telling me it sounded awesome. I installed the bypass tuned SW Chip before I installed the bypass, and it definitely feels better afterwards. I like the Dansk because you can retain all the heatshields for a factory look.
The exhaust smell is definitely a thing though..

No_snivelling

Yes, many on here have confirmed the smell being noticeable with a cat bypass. I noticed it the moment I swapped out my OEM cat for a gutted cat. Now, even with the garage door open, I cannot run the engine for more than a few minutes, but while driving it is mainly the guy behind you that suffers.

mystert

Ive never had a primary muffler on my car since I purchased it so I can only attest to that configuration. I dont feel it made it any louder, only changed the tone and performance.

Foxman

Ha, there’s definitely a bit of smell that goes with a cat bypass, or delete. It smells like, victory.

Foxman

Victory

https://www.dailymotion.com/video/x3639vj

mystert

I am curious, what does a classic short wheel base Porsche 911 from the 60’s-70’s smell like?? They have rich running carburetors and zero emissions controls/catalytic converters. A cat deleted 964 with modern electronic fuel injection compared to those classics is night and day, and even without a catalyst it runs much much cleaner. I could understand those classics smelling “obnoxious” but who in their right mind describes a 1969 911 that way? Maybe a Tesla fanboy but not a Rennlist Porsche enthusiast.

-nick

Closed loop injection constantly cycles between 14.x:1 to 5.x:1 at idle. So you get excess HC and CO when on the rich cycle and excess NOx when it cycles lean. Not sure if that’s the reason for the extra stink compared to older systems but could explain it. The 964 also dips excessively rich on wot.

I would be surprised if a sport cat robbed more 5hp over a bypass even on a modified motor. Foxman knows I’m a hippie but I strongly advocate a sport cat.

This has come up a zillion times. No reason to spend silly dollars- https://rennlist.com/forums/964-foru...l#post18358777

mystert

You must not live in California. Out here any replacement emissions parts needs to have a CARB EO number. Those look like universal cats and the Summit Racing page doesn't list any CARB certification info meaning you'll need to put the stock cat back on to pass smog if you have a smog tech that does the visual inspection properly. After I moved I tried a few smog shops before I found a good one, the first one I took my old E46 to, the tech was a ball buster and started taking off all the engine covers to make sure I didnt have any hidden performance parts etc, if he had seen the sport cat he would have failed the test. The guy I go to now runs the test and makes sure the car meets the tailpipe standards and isnt a ballbuster.

-nick

The location info next to my name should help answer your question? The OP is in Texas. This is a worldwide forum. There aren’t any CARB compliant CA 964 cat options that I’m aware of, but it sounds like you’re not looking for sport cat options anyway? Was your CA-specific post directed toward me? I think I miss the reasoning.

No_snivelling

So what do you do with your cabriolet? Switch back to a stock cat for each emissions test?

mystert

No I would never do that…. 😉

rsabeebe

just bought this from FVD today. couldn't resist the price.

looking forward to hearing how this, the cup pipe, and fister muffler sound together.

Speedster911

Funny you ask this- last weekend I drove my 74 with 2.7, carbs, 2in/2out M&K, 964 cam- its obnoxiously loud, fast and old school to give you a base s of the car. When I came in the house after my outing- I could smell the exhaust on my clothes. Didn't bother me as one winter project is to lean the carbs a bit. My other 74s with CIS and stock exhaust- in my opinion smells like a 74 should, I wouldn't say its abnormally smelly - just the slight smell of exhaust.

I still plan on installing the rennline unit on my 964 - its 10% off currently as an early black friday sale.

Foxman

If you want to add some horse power, and still be kind to the environment, DP Motorsports caries a 100 cell catalyst.

rsabeebe

that looks like a reasonable option for a cat pipe. $730 US is right in line with fabspeed's pricing ($695) and they're the lowest in the market i know of for a full cat pipe. i'd even prefer the 100 cell version of the DP.