sorry duanne 996tt should have been clearer, I am thinking about gutting all four cats out of a stock exhaust.
My options are:
gut all four cats
-might smell gassy not sure if this is only at startup?
-my flash will take care of the o2`s

remove secondary cats leaving primary cats intact
-will not smell
- pass emissions, but this is not an issue for me
-not be as free flowing? Not sure how much is left on the table

removal all four, reinstall 2 100 cell cats in the primary cat location
-wont smell
-probably wont pass emissions, dont really care
-flow just as well as catless? Not sure?
-cost of purchasing 2 new 100 cats sucks

What I really want to know with these options is running fully catless on a stock exhaust going to stink me out of the car at startup, traffic lights etc. with the windows down?
Or not?
Why would I do this instead of buying an aftermarket exhaust? I have had two, and I find them too loud for my taste inside the car, and obviously my car came with a stock exhaust so this is a cheap alternative allowing me to save for the higher end exhausts but still helping out my higher flow needs.
Let me know what you guys think

 

Straight pipes w/o out cats will give you an increase in torque and power but you will sacrifice some low end torque. I've not run an OBD 2 Porsche without cats. It must drive the ECU a bit crazy unless you have it remapped assuming no cats. Depending on your taste of sound, turbo's don't sound too terribly well with straight pipes (IMHO). I did have an OBD 1 (single sensor in front of the cats) '95 993 3.8 n/a that I ran without the cats and 100 octane chip hence no ECU issues. Without the cats and 100 octane it smells like a real car. Several board sponsors make modular exhaust systems that let you swap out between cats, mufflers, or straight pipes.

 

HI,I heard a complete gutted cat system with the muffler pipe hole saw drill trick on a X-50 flashed.. and to tell you the truth,my opinion,it sounded like a boat,,,,,Hollow sound,weird.......But the PCA member said it did perform alot better??Hope that helps

 

Thanks for the info John, I don't plan on doing the hole drill sound mod, just removing the cats. I have been told by an exhaust manufacturer and a well respected tuner who both have done this to there cars at one time (gutted cats only) they both say it retains all the stock sound(quiet) but flows way better. I have been told it's about 80% of what any aftermarket system gives you.
My concern is just fuel smell and what tools made the job easier. Spade bit, start small get bigger etc.
And if adding 100 cells in the primary location help with smell or just hold back flow?
Somebody here must run this, please help.

 

You know with my old muscle cars,I use to gut the cat,,,,then put a sraight pipe in for two reasons,,,,better sound[less hollow] and performance in which keeps the exhaust gases at a higher velocity and more uniform flow then going into the casing body and getting squeezeed down again.....I know Stef fro Europipe put a thread out recently about how to modify the stock cat system.....Hope this helps......

 

I does John, he has been helping me with this already. He just quite couldn't remember how he used to do it as it has been awhile for him. He says it will smell somewhat but again for him it has been a long time. Looking for someone doing this now and his tips to doing this efficiently and advice on the smell.

 

I don't have a 911tt but I got some test results that may help, my car comes with 2 huge brick cats stock. I tested in limp mode on my car just wastgate pressure. I was catless for a while and hated the smell.

Test with stock 2 cats on my car got 7psi in limp mode.

Test with only stock testpipe cat in car. 10-11psi in limp mode.

Test catless 14-15psi in limp mode.

Test with 1 vibrant 3inch 200 cell metalcore high flow cat welded into the 3 inch testpipe and 14psi almost like being catless! Drmatically reduced oder no more rotten eggs and only cost about 1/2 psi of boost. The one I bought was $120 3inch 200 cell.

 

Good info. I found some 100 cells mil. sec cats for $179 that apparently is big in the Mitsubishi evo world. Contemplating if $400 is worth not having the smell.

 

what smell do you speak of, I am catless and do not have a smell...

 

I am going to be in the process of taking off my Cargraphics HJS 200 cell cats and then replacing them with Speedtechs 100 cell cats very soon,,,,thats if I do not sell this Cargraphics system.I hope this fabrication will be worth it,,,but I am also going to change my stock factory headers with another set that I ported/grinded down.I did not coat them because all the coaters were honset with me,,,They agreed with me also,that since they have short pipes,stainless and double walled,,,,,that they retain heat quite well AND on boost the hot flowing exhaust gases will not cool down enough to make a difference inour set-ups......So,take that for whats its worth.....

 

Blockhead your making my day, if I can go without spending the cash on 100 cells all the better.
What did you use to remove the cats, how long did it take? Any tips you found?
You removed all four correct? Not just the two small ones at the o2 sensors?

 

Still looking for advice of which way to go. Sixty percent removing all four and running that way.
Need someone to push me over the top.

 

Gas smell. I had this on my catless Subaru STI. I hated it. On that car it was only about a 10hp difference and definitely not worth it.

 

I do hear that sti's and mitsubishi evo's are bad for stinky exhausts if catless. I have only received info from one 996 turbo guy who says it's nothing to worry about. And I just need a couple more Porsche guys to come forward. I am surprised there aren't more speaking there mind on the subject.
On these cars with a flash running a free flowing exhaust makes a big difference,
But thank you for the info

 

I think most of them are running with at least a 100 cel cat. That is what I will be doing. I have the EPL flash and waiting for delivery of my 3" speedtech cross flow. It has 100 cell cats.