Hey guys, just wondering which would give the most gains... trying to keep the sleeper effect as much as possible . I would like to also know if a tune is needed after the install .
Please only choose one group...

stock down pipe ,stock catalytic coverter + 3" Cat-back exhaust system (UR, CP-E, Borla, AMS , etc.)

OR

3" down pipe , 3" High flow cat. (UR, AMS , etc.) + stock cat-back exhaust system.

Any input will help, thanks guys.

 

The upgraded downpipe and cat would probably yield the most power. Most of it from the hi flow cat. How about just getting a test pipe alone which might make the most...That would be the most sleeper in sound not smell.

 

I just have the DP/O2 and Test pipe with stock cat back. Still making very decent power without the drone of an exhaust. About the only time you hear the exhaust is when rolling up to stop it has a nice low rumble to it.

 

catback is gonna be loud regardless. just go with a high flow cat or testpipe if u wanna keep it quiet. Look at that magnus ralliart in modifed. it was very fast with the stock axleback still on.

 

based on your question of which will give the most gains, it's gonna be the downpipe/test pipe or high flow combo.

the catalyst is the #1 restriction in the exhaust system and will yield the most gains once freed up. also, if you are looking for low noise levels and comfortable driving volume, again the downpipe/cat replacement combo will give the most pleasing results.

catback exhausts on our cars, like most other cars, yield nominal gains by themselves and require other modifications/tuning to become more worthwhile as the stock midpipe/muffler section isnt really all that restrictive until you start running higher boost levels, more airflow/power, etc. not to mention, catbacks can be very loud, especially some of the more popular ones for the ralliart.

edit: if you insist on sticking with a high-flow cat instead of a test pipe, i'd recommend the mil-spec 100cell version as it is shown to be very very close in power gains to those with a straight test-pipe installed. the other high flow cats will be a bit more efficient, environmentally, but will also become more restrictive to exhaust flow as their catalyst efficiency rises

 

Thanks for the info... i'm probably not going the test pipe route, cause its bad for the earth and penalties are pretty severe. I had a feeling the DP + HFC was going to yield the most gains ... does it change the exhaust note?

 

I guess this answers my question, if it changes the exhaust note... thanks

Thanks I'll look it up.

Wow, I really appreciate all the information that everyone here is giving me... you guys rock! I have already ordered the UR Down pipe and High flow cat (just the ceramic version) ... I dont think that my car will hit the 450hp limit that ceramic HFC has. cant wait to install it and go to ATCO raceway and see if I can do better than 13.3sec 1/4 mile. I will post some videos of my 1/4 mile runs. Thanks again guys.

 

Let us know how it sounds. Also I see that you have the GST tune. I don't know if its ok to have downpipe and hfc with that tune. I've seen a post by bryan saying that full turbo back is not recommended with the GST tune eventho you're not going without a catback.
I could be wrong... just a heads up. Somebody correct me if I'm wrong.

 

Someone reported after they installed a turbo back with the GST boost pill map it ran a lot richer 10.1 A/F.

 

You might want to rethink going with a ceramic high flow cat. Here's what Bryan from GST said in a recent thread about them:

"Way more flow with a metal substrate then a crappy ceramic cat. I've done a bunch of tests on them. Search username razorlab.
- Bryan"

 

I have the Ralliart with a UR down pipe and UR steel high flow cat. I initially had the full UR turbo back, had to get rid of the CAT back section cause it was painfully loud. The tuner put the OEM cat-back on, left the down pipe and steel high flow cat. Sounds stock now, except if you listen closely you can hear a bit of turbo whine (no rumble or exhaust note).

Its difficult to tell how much power i lost taking off the UR cat-back section. I haven't re-dynoed it, but will do when the EVO turbo goes on. With the UR cat-back section on the vehicle pulled 255 WHP, and was unbelievably quick and responsive compared to stock (255 WHP vs 195 stock - I guess!). Since the OEM went on, I haven't really pushed it too much, but it does feel as though the top end has suffered a bit. With the full exhaust it literally jumped to 7100 RPM in every gear. (Yeah, the redline was moved up when it was tuned.) Of course, that might be just perception, as it was screaming like a banshee at 7100 with the full UR exhaust. Did I mention that I had the optional resonator and additional muffler on the mid pipe?

 

Hey guys, the UR DP + HFC has been installed... Its definitely lighter and nicer looking than the crappy rusted stock ones. Power delivery is definitely better than before, and the check engine light did not come on. you can hear the turbo a bit more... I will post a vid so you guys can hear or not hear the exhaust note (its sounds like stock). over all, I'm pretty happy with them. I'll be going to ATCO raceway sometime and will post my runs to see if my car got quicker.

Please let me know what you guys think is the best dual port BOV that I can get (would like to be able to set it 100% vent to atmosphere, 50% vent /50% recirculate, or 100% recirculate without having to mess with the ecu). Thanks again for all the info guys.

 

Here's a short vid of me revving my car, with the Ultimate Racing Down Pipe and Ceramic High Flow Catalytic Converter installed... still has the stock cat back exhaust system. dont know whats up with the tinny sound??? but you can hear it rumble, and also hear the turbo a bit more.

http://www.youtube.com/watch?v=Ozb_2ZRrRLY

 

I could definitely hear the turbo whistling. Good vid

 

Here's some pics of the install... Ultimate Racing has really great quality stuff!!!