[GilMikalian]

So my plan is to add the Cobb downpipe to my already-installed AccessPORT. Would this bring me to a Stage 2 or would I need to buy the turbo back. My thinking is that the cat-back adds so little to the overall picture, I think the extra $700 or so would not add much in terms of power I would be able to feel. I'm just going for bang-for-the-buck without sacrificing reliability.

So what do y'all think. Good idea to only add a downpipe or is the full turbo back (which will not be available for weeks according to COBB) the only way to go. By the way, I'm very happy with the volume/tone of the stock exhaust as this is our weekend car and any louder and I'll have to cart my family around in our SUV instead of the STI.

[deegee]

Yes, you can run the stage two OTS maps on just a dp. Full TBE isn't needed.

stage for downpipe only.?,real time map prob.? , - COBB Forums

[RallySportDirect]

That is correct. You can run Just a DownPipe.
Your boost might be off 1-2PSI.
We are running a DP on our STi with a stg2 map, and its working out fine.

Kirill
RallySportDirect.com

[threader]

Originally Posted by GilMikalian

I'm very happy with the volume/tone of the stock exhaust as this is our weekend car

Really? I find it too quiet and isolated inside the cabin. I always enjoy getting out of the car while it's warming up to listen to the exhaust burble when I put something in the trunk.
I keep checking Cobb or Perrin for a catback that will retain the 4 pipe look of the OEM.

[GilMikalian]

Originally Posted by threader

Really? I find it too quiet and isolated inside the cabin. I always enjoy getting out of the car while it's warming up to listen to the exhaust burble when I put something in the trunk.
I keep checking Cobb or Perrin for a catback that will retain the 4 pipe look of the OEM.

Yeah, I'm toning it down for this car. My old ride, the MX-5, was way loud. I just want to keep this car a sleeper. Plus, I'm still new to the turbo game and the turbo whine is fun to hear!

[GilMikalian]

So based on the responses, fair to say that a turbo-back, compared to a down-pipe, is likely to provide only a mild boost in performance and not really worth the extra clams?

[Digitalfiend]

Originally Posted by GilMikalian

So based on the responses, fair to say that a turbo-back, compared to a down-pipe, is likely to provide only a mild boost in performance and not really worth the extra clams?

Pretty much. Most of the power gain comes from adding the downpipe with hi-flow cats (or no cats.) I'm not familiar with the '08 exhaust size, but on my '05 the Cobb downpipe would taper from 3" to 2.5" to bolt up to the stock catback. This definitely results in a bit of restriction and loss of power (maybe 10whp or so.) That is why I decided on a full 3" setup; it was a hybrid Crucial racing shorty DP mated to a MadDad midpipe + Whisper catback. It looked stock, except for only having one hi-flow cat.

If the '08 exhaust is the same diameter (2.5") and you aren't planning on making massive power, then a downpipe-tapering to 2.5" catback is sufficient. One thing to note is that the Cobb unit is a bellmouth whereas some other downpipes on the market use a divorced wastegate design. I went with a divorced setup on my '05 and had no issues with boost creep, even on the coldest days in the winter. That Cobb unit is perfectly fine too.

[pwn]

Originally Posted by Digitalfiend

Pretty much. Most of the power gain comes from adding the downpipe with hi-flow cats (or no cats.) I'm not familiar with the '08 exhaust size, but on my '05 the Cobb downpipe would taper from 3" to 2.5" to bolt up to the stock catback. This definitely results in a bit of restriction and loss of power (maybe 10whp or so.) That is why I decided on a full 3" setup; it was a hybrid Crucial racing shorty DP mated to a MadDad midpipe + Whisper catback. It looked stock, except for only having one hi-flow cat.

If the '08 exhaust is the same diameter (2.5") and you aren't planning on making massive power, then a downpipe-tapering to 2.5" catback is sufficient. One thing to note is that the Cobb unit is a bellmouth whereas some other downpipes on the market use a divorced wastegate design. I went with a divorced setup on my '05 and had no issues with boost creep, even on the coldest days in the winter. That Cobb unit is perfectly fine too.

Is the divorced setup beneficial compared to the bellmouth?

[GilMikalian]

Originally Posted by pwn

Is the divorced setup beneficial compared to the bellmouth?

Good question. The good folk at Cobb indicated that I should keep an eye on boost levels if I wanted to go the DP route w/out a turbo-back with a Stage 2 map. Will a divorced DP help with guarding against boost spikes?

[Digitalfiend]

Originally Posted by GilMikalian

Good question. The good folk at Cobb indicated that I should keep an eye on boost levels if I wanted to go the DP route w/out a turbo-back with a Stage 2 map. Will a divorced DP help with guarding against boost spikes?

No, it won't help with boost spikes. Boost creep is what you need to watch out for. The advantage of a divorced wastegate DP, as I understand it (and I'm no expert), is that there is less turbulence and resistance for the exhaust coming from the wastegate, which allows the wastegate to work more efficiently. This technically should help with boost creep issues, where the wastegate is fully open but can't evacuate enough exhaust to keep the turbo in-check. I had spiking with my stage 2 OTS map, even with the divorced wastegate, but I never experienced boost creep, even with a full 3" setup and one hi-flow cat.

I'll see if I can dig up the article I had on bellmouth vs divorced wastegate setups. It was written by an engineer from Garrett.

[Digitalfiend]

I knew I had posted it here a while back:
Divorced vs Bellmouth

[GilMikalian]

Originally Posted by Digitalfiend

I knew I had posted it here a while back:
Divorced vs Bellmouth

Good stuff. Thanks for the 411.

[chmura]

This is the best setup for the most out of your money since getting a TBE doesn't provide that much hp gain.

Is just installing a DP and Stage 2 map abosultely safe for the car?

[Szumita]

you can, however, you may not hit target boost, as a full TBE is recommended.

[RallySportDirect]

Originally Posted by chmura

This is the best setup for the most out of your money since getting a TBE doesn't provide that much hp gain.

Is just installing a DP and Stage 2 map abosultely safe for the car?

Yes a DP and a Stg2 reflash are perfectly safe. You will be off target boost by 1-2psi. But thats nothing to worry about.