Running a V7 STi. Factory apart from BOV. Looking at getting a cold air intake, and an exhaust for basic performance mods and HP gain.
sw20,
Jan 1, 9:52am
You don't need to be a rocket scientist when building an exhaust for a turbocharged car. It is not some dark art.
1ollie,
Jan 1, 11:12am
LOL WTF! thats mostly rubbish! Compressor surge has NOTHING to do with the exhaust! Also an exhaust will NOT make or take away lag! it may 'feel' more or less due to increased or lost power. And what exactly is boost recovery! lol.
1ollie,
Jan 1, 11:13am
100% incorect sorry.
1ollie,
Jan 1, 11:18am
You have no idea what compressor surge is do you! It has nothing to do with the exhaust side or turbine wheel! It is when your blow of valve does not vent enough of the air or you dont have a well matched turbo to your setup and its when the air builds up pressure and the motor cant consume it or it cant go past the throttle then it vents out the easyest path which is out of the compressor wheel. And who has ever got compressor surge from changing an exhaust! show me an example.
1ollie,
Jan 1, 11:23am
No its not! its the lack of the compressed air having anywhere for it to go and it escapes past the compressor wheel which 'chops' it up as it comes out then you hear 'surge noise'
smoothgroove,
Dec 29, 6:22am
Pros and cons of each for a turbo charged vehicle (STi). Cheers.
hijacka,
Dec 29, 6:30am
Aftermarket downpipe pros= less lag and better spoolup and boost recovery, cons= more compressor surge and exhaust gases, Catback Pros= less emissions and less compressor surge, cons.more lag and reduced spool up time and recovery(that's between gear changes).
morrisman1,
Dec 29, 6:33am
I read somewhere that putting an exhaust with too little back pressure will cause the turbo to overspeed and fail prematurely.
sw20,
Dec 29, 6:47am
Sure if you run it out of its efficiency range. They don't just gain 50,000rpm by fitting an exhaust.
hijacka,
Dec 29, 7:05am
Which is called ''compressor surge'' its the fluttering noise you hear between gear changes and is often mistaken for a bov noise. Its really the sound of the compressed air escaping past the turbine as it has no where else to go, compressor surge leads to turbo failure. the reason you get more surge with a free flow exhaust is because your removing the exhaust back pressure and allowing the turbo to spool more, not over boost its called ''compressor surge''
sw20,
Dec 29, 7:12am
Back pressure is bad.
Compressor surge happens when the engine can't use what you are trying to force into it. You would have to be running some serious boost through a stock turbo to get compressor surge.
Fitting a downpipe and open exhaust isn't going to give you compressor surge on its own.
hijacka,
Dec 29, 7:27am
Exhaust back pressure slows the exhaust turbine down without any back pressure the exhaust turbine doesn't slow down after coming off boost and if there's not enough vacuum to trigger the BOV then the compressed air doesn't have anywhere to go but force its self back on to the compressor wheel and out the intake.Compressor surge is generally heard at low rpm levels were there's not enough vacuum to open the BOV but because there's no exhaust back pressure to slow the exhaust turbine down when the throttle is shut it then exits via the compressor wheel. I would rather run a turbo back exhaust as a turbo will run more efficiently (especially at high rpm)but every positive has a negative doesn't it!
sw20,
Dec 29, 7:36am
The exhaust on my mr2 is about the length of my arm. 3" mandrel bent piping. No mufflers. No surge.
vivac,
Dec 29, 7:48am
If you are on boost the BOV will open, if not, get a better BOV.
hijacka,
Dec 30, 7:27am
Exhaust back pressure slows the exhaust turbine down without any back pressure the exhaust turbine doesn't slow down after coming off boost and if there's not enough vacuum to trigger the BOV then the compressed air doesn't have anywhere to go but force its self back on to the compressor wheel and out the intake.Compressor surge is generally heard at low rpm levels were there's not enough vacuum to open the BOV but because there's no exhaust back pressure to slow the exhaust turbine down when the throttle is shut it then exits via the compressor wheel. I would personally rather run a turbo back exhaust and run a divorce downpipe on to 3'' mandrel as a turbo runs more efficiently (especially at high rpm)but i have compressor surge problems at low rpm, guess every positive has a negative doesn't it!
smoothgroove,
Dec 30, 5:56pm
So will the cat-back exhaust have noticeable power gains!
angel_25,
Dec 30, 8:31pm
It also depends on which type of turbo and intake system you have re Compressor surge.I have a new GFB hybrid bov which is good enough for my setup and run a factory ihi vf23 turbo(which is a ball bearing turbo and quick spooling) it takes the turbo around 15seconds to stop spooling from idle to shutdown. i also have 3'' intake piping from the afm to a pod filter. The compressor surge happens at low rpm between gear changes(not when on boost).Actually the boost gauge still reads vacuum sometimes when surge happens. The only way i can defeat it is by easing the accelerator pedal off and not slapping the throttle shut. What type of turbo do you run sw20! When i was running a td05 20g there wasn't as much compressor surge, perhaps because its bigger and of roller bearing design so didn't keep spooling between gear changes
angel_25,
Dec 30, 8:36pm
not really ,5-10hp!. I would recommend getting a aftermarket downpipe for noticeable power gains, what type of subaru do you have and what mods does it have so far!
hijacka,
Dec 30, 8:38pm
Woops logged in the misses name. Angel_25 is all me, sorry bout that lol
hijacka,
Dec 30, 8:41pm
Its not the compressed air that causes compressor surge it the compressing air that does.
wrong2,
Dec 30, 8:42pm
the easy thing to do with exhausts is to buy the correct size pipes
the hard thing to do, is to put them together properly
jason_247,
Jul 27, 3:59pm
well theres your problem
fyi always go turbo back, cats are a useless POS idea save 1% emissions but use 5% more fuel that will save the trees
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