Is it possible to have Cobb AP stage 2 w/ stock exhaust? From what I've searched, they say it's not possible.

Someone is claiming to have Cobb AP Stage 2 w/ stock exhaust. I need some confirmation. TIA.

I would not recommend using the Stage 2 map with stock exhaust. They tuned it that way for a reason. At the very least, you need a downpipe.

Will the Cobb AP Stage 2 do anything for a stock STi? From stock, I mean stock, exhaust, UP/DP.

I would not recommend using the Stage 2 map with stock exhaust. They tuned it that way for a reason. At the very least, you need a downpipe.
^^^ Ditto ... At a minimum you have to have the down pipe (or a downpipe in general, it doesn't need to be Cobb's) Otherwise you are simply Stage 1 using just the AP ... Your stock UP will be fine even when you do upgrade to Stage 2, but the DP is needed for Stage 2 and the TBE is highly recommended ... :D

Thanks.

Stage 2 = more boost
More boost = more heat
Free flowing exhaust lets the heat escape better.

There is more to it than this, but just wanted to make this simple point.

If you install stage 2 without an aftermarket downpipe or new exhaust, how much HP do you think is lost?

I have a e-mail from trey. Here it is:

Peter,

You can run the Stage2 mapping with that configuration. You may see
slightly less than the target boost due to the lack of a true turboback
but the end results should still be nice. Most importantly, it'll be safe.

Thanks,
Trey Cobb.

Now the question to Trey was if I could run stage 2 with a stock STI catback on a WRX with a Helix Catted DP.

Hope this helps.

If you install stage 2 without an aftermarket downpipe or new exhaust, how much HP do you think is lost?

It's not a matter of losing HP, it's a matter of running an improper map for your setup. I would imagine you could run dangerously high EGT's raising the boost that much and keeping eveything stock, but if you like to play with fire be our guest. If you have a way to monitor EGT, Boost, AFR, and knock, then I would give it try, otherwise a DP is cheaper than a new short block :)