Mixter

Just have the primary cup installed and the sound is just right for a cab. I'm thinking that a cat bypass would not be good for a cab because of the fuel smell and probably too loud for top down driving.

time666

I'm glad this threads come back, some good info. I changed my cat for a cheap straight bypass pipe off eBay and soon after I could smell the exhaust fumes smell much more noticeable, especially when stopping in traffic. I thought it was a sign my engines going to need some attention sometime soon, but having read this it may just be due to my cat bypass. Hope so anyway.

Recently I have also noticed some blue smoke from the exhaust on tick over which seems to be intermittent, anyone know if the straight pipe bypass could cause this? May just be coincidence. Just thinking could the change in resistance throw out the mixture somehow?

greg1990964

Good question on the blue smoke at startup. I have never seen it until I started my car with new cat bypass to show a friend the sound. It made a puff I chalked up to it being bone cold and gave it a couple of revs. I know, I know. A child with a new toy syndrome. So the question is, does a real cat eat up any blue smoke? I doubt it. Prob just blew some oil out that had seeped down.

John@Fabspeed

Has the blue smoke stopped? Sounds like it may be a bit of oil that had seeped down. Keep us updated!

time666

Mines not at start up, seems to have intermittent small amount of blue smoke after being out for a run. So fully up to temp. Maybe coincidence I started noticing after cat was fitted. Just hoping it may been 'normal' with having a cat installed. No longer thinking its related now.

greg1990964

To answer above, no more blue smoke. I am
sure that puff was caused cause I romped on it
the second I started it and it was dead cold. I just started It after sitting for 2 days and not a puff.

John@Fabspeed

Great! Enjoy your piping!

espanolie

i've read a lot 'bout catless and its attributes. i'd love to hear one live and draw my own conclusions. anyone local to the los angeles area would be willing to meet?

c didy

What is the deal with the exhaust smell? My '72 has webers, runs rich and still doesn't have as much fuel smell as my buddy's 964 with cat bypass. Is his car just running even richer than my old school 911 technology from the pleistocene when cats were not yet on the horizon?

greg1990964

No idea about fuel smell. I don't smell anything with cat bypass.

c didy

You may not but most do. It's not a fuel smell, it's an exhaust smell. It is one of the comments most often associated with cat bypass pipes in 964s. And my friend’s 964 does smell much different after installation. It also has a much stronger exhaust aroma than my ’72 running rich with Webers . I would think the 964 with dual plug ignition, computer control, and fuel injection would have more complete combustion and less smell than my car. Does that make sense? My 42 year old hot rod burns cleaner than the fancy pants 964. Not as far as emissions probably but as far as smell.

time666

Yeah I get that, I thought it was just coincidence but now realised it must be related to my cat pipe. Even had a guy on a motorbike riding behind me and when we stopped in a queue he pulled along side me and said the cars nice but smells like it's burning some oil or running rich !!. Wasn't a visual thing.

I know what you mean it's not a fuel smell, I notice when I come to a stop I can smell it then in traffic.

964Carrera4

I can confirm that a friend's 964 really STINKS BAD because of the cat bypass pipe that he recently installed for more performance.

I was following him on 964 group drive in my convertible and after a few miles of that, I had to take a spot farther back in the group of cars that we were traveling with.

greg1990964

I actually hope my car smells bad. I like to offend and If I can offend a little more, then that thrills me. Maybe my ex will be driving behind me one day.

x98boardwell

Good info. That is the route I will probably take as I also have a Cab.