Straight out downpipe, no exhaust?
 

Less exhaust / larger diameter exhaust aids in spool right? So lets say for a race car that need not worry about passing a smog or conforming to a certain set of class rules, would it not be crazy spool-tastic for the downpipe to be the only exhaust on the car? Would this sacrifice low end when the turbo is not in full play? I remember running straight out of the header for a day when I was NA and it felt slower.. LOUDER but slower. Or would this be good for power?
Maybe have the outlet angled down a bit so it's not shooting down the transmission tunnel? Talk to me. I'm brewing things.
-Ryan

You might get kicked off the track for being too loud

I run just a down pipe - It was supposed to be temporary but I never got around to making the rest of the exhaust last year. It was obviously loud, and you could hear the turbo spool from a mile away during normal driving so it killed the stealth factor. I think it helps with response a lot but never had a before/after with full exhaust. Hopefully soon though.

my autox has no sound restrictions. I'm asking as if this were for a race car with no regulations to avoid this thread taking a tangent into it being too loud or not passing smog, but I'm thinking about a custom downpipe with a cutoff switch before the flange that mates to the cat. Flip a switch in the cockpit, go from tame street-able 2 1/4" exhaust to a dump pipe before the cat so bypass the whole exhaust. It's not expensive and would be pretty sweet I think... but this is a car that needs to be as fast as possible on corner exits and such, not just between 5k and redline in a straight line, so I need to be sure it won't kill the lower end of the powerband...

You will have negligible spooling difference between a catless free flowing 3" exhaust and an open downpipe.

but i don't want a catless 3" exhaust pipe. I drive on the road. that would not pass smog and would be too loud. The point is to have a civilized streetable exhaust for the road and at the flip of a switch change to a no backpressure, shortest piping possible setup.

get a exhaust cut out. jegs sells them makes your exhaust dual purpose.

That is what I'm planning on doing. Run my tame 2 1/4 borla duals everyday and open a cutot for taking it to the track. I plan on building a pipe in place of the cat that has the cutout in it.

This has been an on going debate in the SRT-4 crowd. It has been shown that a 3" dump DOES provide more power, if tuned correctly. The problem is, there is a difference in the tune with the full system and a dump. One person finally decided to tune and dyno with a full system and tune and dyno with a the dump. He was able to manage to get an extra 24 horsepower or so.

Ryan, you've heard my car. It's a BEGI separated gases 3" DP to a 3" high-flow cat to a 3" Enthuza. I drive the shit out of it on the street, and it is nowhere near too loud. I have a section of 3" pipe to make a testpipe, and I had the flanges, but I never got around to it.

The bit about needing different tunes makes sense... not that that seems terribly difficult to do if you are running MS or the likes.
Sav - problem is, I like my exhaust a lot / I don't want to spend the money on a whole new exhaust when I already have a 'nice' exhaust even though it's not optimal diameter for a turbo considering how many other areas I'm dumping money into right now. Main thing I thought would help though is the lack of having the gases have to pass through any cats...
-Ryan

If the exhaust gas came right out of the downpipe or header, wouldn't it hurt with car with those temperatures or no?

So long as the gases are directed away from the car, it's fine.

Ryan, that's why I never bothered upgrading from my stock system. You REALLY should upgrade the entire exhaust, but yeah, if you wanted to, you could dump post-DP and get a bunch more spool and power (and noise).

You need to upgrade your DP, though. NEED. 2" DP FTL.

You know, I've considered this too, but for different reasons. I like stealth. I would prefer my car appear 100% stock in every way. I'd like to keep my stock exhaust just so it's quiet and sounds stock. Have a dump valve for HP. All sounds good till you consider the tune aspect. I was going to have MS control my dump valve, so I guess I could have it map switching too. Still, a lot of work. Not really sure how I'd set it all up.

Anyway, try it and report how it works.

Anyone know how badly it would mess up my tune if I were to tune my car with a 2.5 inch DP with stock exhaust, drive to racing event with stock exhaust, unbolt stock exhaust and run open 2.5 inch DP? Would it cause me to run dangerously lean?

I'm running a 3" open DP on my shit. Loud as hell.. but I love it. Track only car.. but ima get kicked off with my luck.

I think everyone here owes it to themselves to drive their car with an open downpipe at least once. The noise is GLORIOUS.

I run open downpipe, dumps under the car right behind the drivers seat. It has a cat.


Its not THAT loud, I avent had any police attention or anything, plus it sounds sooo good.

i have ran open DP and a full exhaust on my car. didnt feel ANY power loss going from a 2.5 open DP to a 2.5 full exhaust. but the open DP is stupid loud! idle is ok, but with any throttle at all, it sucks ass.