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Down pipe question.


Scubaru03

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Where are you located? Do local laws require you to have a cat?

 

Some will jump in & say the responsible thing is to get a catted DP. I have one, and I have no complaints. I'm not sure what you gain by getting a non-catted DP.

 

This probably doesn't answer your question. I bought my car used with a cat-back exhaust, so I can't really say one way or the other.

Tits mcgee
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Yes, catless DP means catless, it bolts to the mid pipe. You will still use the OEM rear O2 sensor.

 

So that eliminates the second also or just the first wouldnt i need to delete both o2 sensors if no cats. Sorry just little confused. Car has 3 cats one in up pipe one in down pipe and one before resonator. My understanding is a aftermarket dp will eleminate both cats on outlet of turbo.

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1 uppipe, 2 in the downpipe. Factory downpipe is 2 piece. You can occasionally find a shorty downpipe. But the majority of down pipes are 1 piece.

 

Thats what i thought. Just wanted to make sure. Thank you. Also if i want to keep my stock catback is that gonna kill performance. I wouldnt think except for the smaller diameter pipe. Wanted to double check. I want a catback but a quiet one and the funds probably wont permit. Thank you for clarifying.

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Not with just a downpipe. If you got a much larger turbo, the stock catback would start to be restrictive, but the downpipe is the main chokepoint on the stock exhaust system.
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I will be getting diff turbo. Looking at the bnr 16g. My vf40 has 154k on it. Still pulls but know it will fail eventually. I know my odds of having another one last this long is slim to none from what ive read. Vf52 just is too expensive but never know maybe ill hit the lottery.
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By different turbo, he meant a real turbo. Something that will make lots of HP.

 

What your looking at is basically stock. I have stock mid pipe with stock fueling and make decent whp.

 

You'll want to replace the up pipe with a catless one also.

 

Remember, it's all in the tune. Get a good Tuner, one who knows these cars.

 

I recommend Mike Kinsman of http://www.tuningalliance.com you can get him thru is thread in the Vendor forum here too.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

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For a 16g you may not need a tune. IMO these cars should not be on the stock tune anyway's.

 

There is a timing flaw that is not good for the valves.

 

I get better mpg with a tune then on the factory map. That's common.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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For a 16g you may not need a tune. IMO these cars should not be on the stock tune anyway's.
What are you smokin man? :confused: You know better than that! He needs a tune, unless he decides to run WG pressure only, but that would suck. Plus, he's getting a DP and UP.

 

Tune, period, no ifs, ands, or buts.

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It is true it reduces back pressure but the more air you can get out of the turbo the better. If you open the exhaust at the downpipe there may be too little back pressure where you might lose a little bit of top end, but with the full 3" exhaust you are fine.
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What are you smokin man? :confused: You know better than that! He needs a tune, unless he decides to run WG pressure only, but that would suck. Plus, he's getting a DP and UP.

 

Tune, period, no ifs, ands, or buts.

 

Yes, your right, I typed that just before leaving work and was in a hurry.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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i heard that its bad to use full 3'' from turbo all the way back because you wont have any back presser. is that true? so should you go with a 2.5'' some where in the exhaust?

 

It is true it reduces back pressure but the more air you can get out of the turbo the better. If you open the exhaust at the downpipe there may be too little back pressure where you might lose a little bit of top end, but with the full 3" exhaust you are fine.

 

True.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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I've heard this too, but I personally think it's incorrect. There's no reason why backpressure post-turbo would help with performance. The only issue would be if the WG is too small, and there's so little backpressure for the turbine that you end up with boost creep because the WG can't bypass exhaust quickly enough. This has been seen with some VF52 setups here.
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Alright so you guys are saying to cool to run the 3'' Downpipe with my 3'' cat back I already have? And I'm just running the stock turbo.

 

Yes, it's ok.

 

It is also true that turbo race cars have a basically open DP. Some as short as possible to direct the exhaust away from the car. Or up thru the hood like some of the Honda's.

 

I have been told that on a street car you want a little back pressure to help mid-range power.

 

http://i185.photobucket.com/albums/x40/92Si/DSCN4017.jpg

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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I have been told that on a street car you want a little back pressure to help mid-range power.
Yeah, I've seen mention from places of that too, but I have yet to see an actual explanation of why, so I'll just have to disagree with it for now. :)
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