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Old 04-09-2008, 03:01 PM   #1
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Default 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

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Old 04-09-2008, 03:09 PM   #2
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You might get kicked off the track for being too loud
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Old 04-09-2008, 03:11 PM   #3
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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.
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Old 04-09-2008, 03:19 PM   #4
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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...
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Old 04-09-2008, 03:29 PM   #5
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You will have negligible spooling difference between a catless free flowing 3" exhaust and an open downpipe.
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Old 04-09-2008, 03:56 PM   #6
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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.
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Old 04-09-2008, 04:00 PM   #7
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get a exhaust cut out. jegs sells them makes your exhaust dual purpose.
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Old 04-09-2008, 04:10 PM   #8
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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.
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Old 04-09-2008, 04:23 PM   #9
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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.
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Old 04-09-2008, 04:28 PM   #10
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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 **** 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.
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Old 04-09-2008, 06:32 PM   #11
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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
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Old 04-09-2008, 06:35 PM   #12
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If the exhaust gas came right out of the downpipe or header, wouldn't it hurt with car with those temperatures or no?
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Old 04-09-2008, 07:58 PM   #13
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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.
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Old 04-09-2008, 08:02 PM   #14
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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.
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Old 04-09-2008, 08:10 PM   #15
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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?
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Old 04-09-2008, 08:38 PM   #16
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I'm running a 3" open DP on my ****. Loud as hell.. but I love it. Track only car.. but ima get kicked off with my luck.
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Old 04-09-2008, 08:40 PM   #17
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I think everyone here owes it to themselves to drive their car with an open downpipe at least once. The noise is GLORIOUS.
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Old 04-09-2008, 08:48 PM   #18
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Old 04-09-2008, 10:10 PM   #19
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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.
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Old 04-09-2008, 10:19 PM   #20
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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 ***.
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