How can you run catless and not have a stinky exhaust? Smells like rotten eggs. Unless electric car lol.

 

Had a 66 chevelle, 67 barracuda, 72 vette, 89 z28(I gutted cats) all these cars were pre cat and I gutted the camaro's myself. I didn't notice any bad smell with any of them. Atleast what you would except nothing hideous. No rotten egg smell as some guys say. But I want to make sure with this exhaust before I weld it all together than spending the 400 for 100 cell cats is justifiable.
I would rather avoid this extra expense if possible but don't want to drive around in something that the vapors will give me a headache and be forced to redo the welding work again to install two small cats.
That's all anybody back me up here?

 

I don't see how one car can smell and another one doesn't but who knows. I have buddies who say they don't notice the smell either. To me it was horrible I have to stay in my car for little while after pulling in garage, and forget about driving in traffic with windows down lol. I was actually surprised at how well my vibrant race cat cut down on the smell being its such high flow. 75% less smelly and no rotten eggs smell.

 

I had no cats on my 996tt before my current exhaust and never noticed any smells at all. I did a few long trips with the family and my (overly) sensitive wife never mentioned anything either. I plan to go catless again if I downsize my piping to make up for the loss.

On the other hand, I have a 1977 bronco without cats. On that truck, you can smell it from 15 ft away.

I think it has a lot to do with the fuel conditions. The 996tt is a very very efficient running car and I doubt the ECU ever dumps much more fuel than will be burnt in the engine. The older carb'ed cars are more of the "close-enough" mentality.

 

Every performance car Ive owned has been catless and I never had a problem with smell. A proper tune key. Boosted car+catless=great.

 

You guys rock!!!! Decision made, gutting everything!!
Will post seat of the pants results and what method I use. Contemplating just cutting it open and pulling the cats rather than drilling it all out. Unless you guys point me in another direction.
Will be comparing a full 3 inch straight thru system a fabspeed gen3 twin can and this soon to be gutted stock exhaust.
It won't be dyno numbers as I dont have access to one but I know what an aftermarket and stock exhausts feel like with a epl stage 2 flash on a k16 car. Hope to reclaim some of that quicker spool I lost while maintaining a quiet interior. Plus my costs, so far $150 for a used stock system. Keeping my original stock incase this all goes sideways.
Will keep you all posted
Thanks

 

Nothing like the smell of catless and race gas

 

HI Gearhead,I am glad you have your mind made up now.....But..I have a stupid question,since performance is an issue.....How do you know how much you are going to gain taking all the cats out because you said you were not going to do the hole saw trick for the mufflers......Thus ,that might be your weak link,the mufflers,no matter if you take all the cats out or not...Just my thoughts to help you out.....

 

a little late to the discussion but if i were and i was doing all the welding work I would flange the exhaust, it will probably take you an extra hour or so now but it gives you the option of changing out the cats to cat delete of 100 cell cats. Also, a better option for exhaust might be keeping the primaries and deleting the rest of the muffler, my friend ran this set up with good results.

 

The info I collected states that running a stock exhaust minus cats only you will gain back 80% of what any aftermarket will give you but still sound stock both outside and inside.
This info was validated from a tuner who runs this on his personal car as he too wanted to be able to make phone calls while driving.
I rather not say who as he himself is partnered up with other exhaust company's and I don't want to remove food off anybody's plate if you get my drift.
But he is very well respected and has the ability to test his results so I take his word like it's carved in stone.
Granted this is only 80% which is more than enough of a difference for me to buy a second oem exhaust and see for myself.
As far as running only the primary cats which would help emissions and any possible smell, a highly respected exhaust manufacture I have been speaking with who has helped me alot with ideas said that the removal of all cats is by far the best as any cat works like a bottle neck impeding flow.
It maybe the best of both worlds for guys wanting quite and flow. And for $150 it's worth a shot.
Will post anything I figure out.

 

Can you take some pictures when you open up the OEM exhaust and some pics of the work you will do on it. I'm curious what the inside of it looks like....

 

Of course, I will share what I learn.

 

By tune you mean pulling fuel down low rite? I tune only ant WOT not under 30% throttle so maybe that why mine more stinky under regular driving. If you pull fuel everywhere in the tune it eliminates the smell but also you gonn run hotter all the time as a result rite? Cause from the lean gets rid of odor but runs hotter? You are rite catless better for turbo! On my car a high flow cat only costs 5hp I know someone who dynoed before and after. So not a great loss of hp trade off.

I would atleast replace with straight pipe to increase flow.

 

That would be insanely loud. Something I am trying to avoid, most aftermarket systems I found to loud, for me.
This is not the case for everyone but I don't think I am alone.
On a 911 the exhaust tube for straight pipes is like zoomies on a dragster they can shot flames as well if that's your thing, but teeth rattling loud. I agree it's hard to beat that level if flow but the volume is not worth it.

 

You will notice the lost mid range torque. At least off boost. My car was measured at 3 PSI back-pressure at full tilt by GIAC running 1.3 bar sustained to redline. It's an off the shelf 70mm (European size) Remus exhaust with 100 cell cats. Cat-less and even cats with straight pipes require a compromise that isn't worth it on street car. You need the pipe length to get proper scavenging to get the torque.

IMO not worth the benefit to the environment or loss in torque to run cat-less or cats and straight pipes.