3" downpipe to Stock exhaust?

[Hustleshark206]

I want to let me 91' SS breathe easier and let that beautiful boxer rumble shine through a bit more than my stock setup allows. I want to put an after market WRX/STI downpipe on it and have an exhaust shop extend my stock midpipe to accommodate this. I have read many thread here about doing this but all of the aftermarket downpipes are 3". Can this be adapted to my stock catback? Will it be worth it or should I just go for a full 3" TBE? I am not too awfully concerned about the noise. Here in Seattle there are TONS of loud subies and it seems well tolerated as long as your are not being a dumbass.

I was looking at this downpipe because it has the bung located at the top like our stock set up.

Thanks guys!

[gijonas]

In my opinion it kind of defeats the purpose if you just end up bottlenecking it like that
Just save up for a tbe.






.

[kimokalihi]

I wouldn't waste your money if you're still going to keep the stock piping and muffler. But I have a 3" downpipe for sale if you want to lol. $50 I'm located 10 mins south of olympia.

[Hustleshark206]

I wouldn't waste your money if you're still going to keep the stock piping and muffler. But I have a 3" downpipe for sale if you want to lol. $50 I'm located 10 mins south of olympia.

^Can you PM me a picture of it please? Sounds like a full 3" TBE is the way to go. I thought it would bottle neck the exhaust going that route too but it seems like some have done it that way. Thanks guys.

[ericem]

I just put a 3" dp bellmouth catless and bolted it to the stock mid. Doesn't smell except when I floor it sometimes according to friends behind me + it makes the exhaust louder outside, but inside the car its the same. Supposedly it helps performance although I think my up pipe to turbo gasket is leaking + the stock mid pipe cat could possibly be clogged.

[cj91legss]

ok, so what about if you did 3" all the way back to an STI axleback... i believe they're 2.5" would there be power loss?

[kimokalihi]

Nah. 3" exhaust is good for like 1000hp or something. So I'm sure 2.5 would not be a restriction especially coming off a 300hp car.

[cj91legss]

yeah that's kind of what i was thinking too i really just wanna keep mysaelf under the radar, and quiet the inside of my car.

[kimokalihi]

Exactly. Loud exhausts are for racecars and ricers. STIs are pretty quiet right?

[cj91legss]

yeah

[wtdash]

It's been a couple years since I did this, but the 3" bell mouth (looks like the one in the pic) I installed hooked up to the rest of the stock SS exhaust just fine...might have a had a small exhaust leak to fix....can't remember for sure.

It made a difference...maybe not on the real dyno, but the car would rev more freely and get to redline easier. Do it and get a full 3" back when you can.


I also have the STi axle-back. It's 2.5". WRX is same as stock @ 2.25", IIRC. I doubt it's costing me any HP, but I'm only about 180HP/230 torque to the wheels w/my setup.

TD

[impreza_GC8]

I had a 3" DP with the stock exhaust as well, it required a custom flange. I still have it all laying around somewhere.

[Mattheww044]

Exactly. Loud exhausts are for racecars and ricers. STIs are pretty quiet right?

or people that like hearing their cars KIMO!! I have 3" TBE and no cats, the only thing I have is a gutted muffler. I like the sound, but I wish it was a little louder....

[93Leg-c]

I also have the STi axle-back. It's 2.5". WRX is same as stock @ 2.25", IIRC.
TD

Are there certain years where the sti axle backs were 2.5"? Every one I've looked at from '04-'06 all had 2.25" piping. A lot of guys on NASIOC say their sti axle backs are 2.5" and when I ask them to verify it, they all say it's 2.25". I'd like to find an sti axle back with 2.5" piping if it really does exist. Anyone know for sure?

[brand]

It is perfectly common on later cars to run a 3" DP into the stock midpipe and muffler. I run that and a Cobb Stage 2 map on my STI. The major restriction is the downpipe. If my 2.5L with a bigger turbo doesn't need more than that, I'm sure it'll be more than enough on a Legacy unless you've got some kind of swap going on or a seriously built engine.