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Modding 04 FXT. COBB exhaust.....

11K views 58 replies 13 participants last post by  brad84 
#1 ·
#12 · (Edited)
He's talking about the pre-cat. The cat that's in the up pipe does very little to reduce emissions. It is mainly used to reduce emissions before the secondary cat warms up. The biggest problems with it are that it reduces spool by restricting airflow to the turbo, and it is known to break apart and shoot chunks of metal into the turbo and destroying the fins. All 06+ turbo Subies have no more pre-cat.
I have also kept my secondary cat because of emissions concerns.

Forgive my ignorance but isn't bigger better on a turbo? STi is only 2.5" when it might be more beneficial to go 3".
You need a 3" downpipe in order to go to stage 2, either on the stock turbo or the VF39. A 3" cat back helps increase flow and frees up some additional power, but it does come with a penalty in sound (unless you like the sound, which I do). There are some quiet 3" catbacks available from MadDad.

The Cobb maps worked really well on my car, my custom tune improved things but my tuner (Doug Wilks @ TopSpeed) was impressed with how well the OTS did for it.
You know, they have been excellent on my car too. Both the Cobb stg 2 and the Cobb VF39 map have been awesome. When they took a look at the dyno plot and A/F ratios they (Cobb) told me they can do very little to improve on it. Sure there's some power to be had, and having multiple maps would be great, but I can wait for a little while.
 
#9 · (Edited)
Well fun fact; the Cobb TBE isn't a true full 3". At the DP/mid-pipe junction there is an area that is 2.5". However this small area is commonly modified as I have done it on mine to get a true 3" from turbo to exhaust tip. I also modified mine with a flex joint.

I have a Cobb catback and LOVE LOVE LOVE the sound. I would be surprised if they actually had one though. Most resellers just post up the items and then they are drop shipped. Call and find out. If you have the money i would definitely recommend the Cobb TBE
 
#19 ·
Yeah, just the 3" downpipe will be fine for running OTS Stage 2 maps. You can search cobbforums and find posts mentioning that. I recently upgraded to a full 3" exhaust and the power difference isn't very noticeable, at least without a re-tune. I was always able to hit target boost without issues before. What IS noticeable is sound -- the car is LOUD. This is with the MadDad Whisper, which supposedly is the quietest option out there.

So, unless you like the sound, just get a catted aftermarket downpipe. I had a Cobb before and am running v4 Invidia now, both are great quality. Cobb has an O2 bung in the bellmouth if you wanted to install a wideband, Invidia does not.

Stan
 
#20 ·
another cobb tbe owner who loves his exhaust. the sound, fit and finish, and looks are unrivaled! i still have the taper down to 2.5" then back to 3" again w/ no ill side effects. mine is also catted, wouldnt have it any other way. must be my old age LOL, but this is the first catted subie ive ever had, i got sick of the stinkyness... but youll def want a new catless uppipe, not only for power - but godforbid it craps the bed and sends the broken pieces through your turbocharger!
 
#33 ·
If someone just runs Stage 2, is it worth it to get a Cat-less up-pipe?
:shrug:

What year is the Forester? If it's 04-05 I'd recommend getting a catless uppipe if you plan on going stage 2
but youll def want a new catless uppipe, not only for power - but godforbid it craps the bed and sends the broken pieces through your turbocharger!
If you're doing exhaust mods, you shouuld really consider a catless uppipe.
 
#41 ·
Bosal makes (or made) a catless up-pipe with OEM looking heat shields.

Nice if you're concerned about failing the visual inspection some states have as part of their emissions testing requirements. That said, I can barely see my up-pipe (and EL header for that matter) unless my car is on a lift and I can look up at an angle past the subframe.
 
#43 ·
Is that guy me? If so, than it is missing the upper shield. The lower shields are still intact. You could always wrap it if you want.

All aftermarket uppipe I know of, except the Bosal, have no shields at all or flex joint. In all seriousness, when it comes to uppipes (for a stock or near stock car) it's not going to matter what uppipe you're running so long as it's catless. Just make sure you get a quality one that isn't going to have bad weld that crack over time. The OEM is great because you know it's going to fit, it's going to last, and it has the OEM look.

I would say go for the cheapest one, of quality, you can get.
 

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#45 ·
Hahaha, believe me i'm not offended. If you don't know the answer yourself you have to get a second opinion. It's the only way you'll ever learn. I posted up the pic just so everyone else could see what you're talking about. There's no obligation to buy from me either. It's your money, spend it on what you want. My feelings won't be hurt.
 
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