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Discussion Starter · #1 ·
Yesterday I got my car stage 1 tuned with everything stock except a BOV which i might switch back to the original setup for power advances..

Thinking of doing a 3" Downpipe + full exhaust using my welder an 3" piping, if i reset my battery this will reset my tune to the day I got it.. will the tune like a 3" exhaust better? I have a garrett turbo which was supposably the big T in 2003
 

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I'm pretty sure the TD04L-14T is the "T", the Garrett is the smaller "t"... regardless of year.

A 3" DP will only be of long-term benefit if the map is tuned for it. Removing the battery - will return the ECU to learning mode, but it will quickly adapt back to what it expects. It will feel quicker, no doubt about it... but not for long.

It's all down to the tune really. A BSR Stage 3 tune expects a 3" DP, but not a 3" full system. I run S3 with a full 3" including race CAT... it's louder but I'd put money on it not being any quicker than with a 3" CAT and 2.25" system.
 

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With a downpipe your power will come on quicker due to the reduced turbo spooling time but in the long run doesn't make much difference at all. Brian at Vtuner runs his stage 1 close to 300hp on his 2.0T with an upgraded turbo but a bone stock exhaust system.

I have a 3" dp with a homemade 2.5" system. Only difference from stock is the sound and I'm considering going back to the stock system from the downpipe back to quiet things down. It gets annoying after a year or so...
 

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With a downpipe your power will come on quicker due to the reduced turbo spooling time but in the long run doesn't make much difference at all. Brian at Vtuner runs his stage 1 close to 300hp on his 2.0T with an upgraded turbo but a bone stock exhaust system.
I'm not familiar with VTuner, so perhaps I shouldn't comment... but I don't believe that for a moment.

You can't ask a standard 2.25" DP to handle a 50% increase in power, not without introducing an artificial restriction.

A 3" DP will make a difference in the long term, but only if the map is expecting it.

The idea of any exhaust system is to remove gases as quickly as possible (volumetric efficiency). If you increase the volume of gas, you must also alter the flow velocity to compensate.

N/A motors (and ricers) think bolting a 4" exhaust to their Civics will increase HP. It doesn't... it has the opposite effect because it reduces volumetric efficiency. A 4" exhaust can handle more gas, but the velocity drops to such an extent, the N/A engine can't run correctly (no back-pressure).

The same applies for turbo engines, although we don't need back pressure to run normally. You still can't bolt a 4" exhaust on and expect an increase in HP though, for much the same reason.

On the flip side, if you keep a stock exhaust but increase the volume (by remapping), you also increase back-pressure. The only way to reduce it is to increase pipe diameter, particularly at the DP.

Too little and you'll get back-pressure, a drop in performance and a stressed turbo.
Too much and you'll either reach the point of diminishing returns or slow velocity down.

Exhaust design is a catch 22.

Small pipe ID:
Hotter gases move quicker, volume potential is reduced but flow rate increased.

Big pipe ID:
Cooler gases move slower, volume potential is increased but flow rate decreases.

We've not mentioned the venturi effect either, which builds velocity (think 4-2-1 headers).

The general consensus is 2.5" up to 300BHP, 3"+ beyond that. Our bone stock is 2.25".
 

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Discussion Starter · #6 ·
no, it will just reset to the second ur car was flashed with the new tune.. then ur car will go 100 miles back into learning mode
 

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Oh I didn't understand the part where you said that. I'm aware of the 100 mile thing. Just wanted to make sure you weren't confused.
 

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I am certainly not trying to start a "my tuner says this and that so it must be true" threads. We all know there are enough of those. I am also familiar with basic exhaust flow theory as I do make my living as an auto service technician, however your explanation is definitely helpful. That said, I am willing to trust his dyno claim from a strictly hardware point of view.

http://www.saabcentral.com/forums/showthread.php?t=227182&highlight=vtuner+stage1
 

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A 3 inch cat , k&n drop in And stage 2 tune could expect what gains ?
Stage 2 doesn't have a software tune, just catback exhaust I believe. K&N will give you no noticeable performance gains. If youre thinking about doing anything exhaust wise, i'd say go with a GS downpipe, or an OBX downpipe. I'm running a CAI (mainly sound) with a FMIC (slightly more top end power) OBX DP (cat and resonator delete) to stock muffler, and only at JZW stage 1 and it pulls pretty damn good. The exhaust is all welded except for the DP to cat, and cat to turbo- theyre all bolted. You'll only get gains from the downpipe and the intercooler...and theyre well worth it for sure. But it all depends what your goal is with your car ;)

I'm assuming this is all pretty close to JZW and BSR plans as far as power is concerned...they all seem pretty similar.
 

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does the exhaust disconnect anywhere but where it bolts to the turbo?

The catalytic converter bolts directly to the turbo on a stock setup, then the stock exhaust bolts to the bottom of the cat.

Maptun has a stage 2 tune which tunes for a catback, although I'm not really sure it's needed as all the restriction remains from the stock cat (been discussed quite a few times on here).

As far as the bigger turbo stage 1 vtuner thing, there are a lot of cars out there with bigger turbos than the TD04-14T (which I'm not even sure the OP has this turbo as he said he's got a garret) which also need to meet emissions regulations and go through a restrictive exhaust. The only difference I see is that our cats are directly off the turbo, which creates a lot of heat and immediate restriction of the exhaust velocity.

I really don't see the point though of leaving the stock exhaust (the cat specifically), you put a lot less stress on the turbo from both flow restriction and heat alleviation by going the 3" downpipe route. I feel a lot more comfortable with the GS downpipe and high flow cat ( especially since it's at least 6-8" further away from the turbine exit).
 

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I'm not familiar with VTuner, so perhaps I shouldn't comment... but I don't believe that for a moment.

You can't ask a standard 2.25" DP to handle a 50% increase in power, not without introducing an artificial restriction.

A 3" DP will make a difference in the long term, but only if the map is expecting it.

The idea of any exhaust system is to remove gases as quickly as possible (volumetric efficiency). If you increase the volume of gas, you must also alter the flow velocity to compensate.

N/A motors (and ricers) think bolting a 4" exhaust to their Civics will increase HP. It doesn't... it has the opposite effect because it reduces volumetric efficiency. A 4" exhaust can handle more gas, but the velocity drops to such an extent, the N/A engine can't run correctly (no back-pressure).

The same applies for turbo engines, although we don't need back pressure to run normally. You still can't bolt a 4" exhaust on and expect an increase in HP though, for much the same reason.

On the flip side, if you keep a stock exhaust but increase the volume (by remapping), you also increase back-pressure. The only way to reduce it is to increase pipe diameter, particularly at the DP.

Too little and you'll get back-pressure, a drop in performance and a stressed turbo.
Too much and you'll either reach the point of diminishing returns or slow velocity down.

Exhaust design is a catch 22.

Small pipe ID:
Hotter gases move quicker, volume potential is reduced but flow rate increased.

Big pipe ID:
Cooler gases move slower, volume potential is increased but flow rate decreases.

We've not mentioned the venturi effect either, which builds velocity (think 4-2-1 headers).

The general consensus is 2.5" up to 300BHP, 3"+ beyond that. Our bone stock is 2.25".
Mostly true but not completely. For a turbocharged car, the ideal exhaust is actually a short, conical, length of pipe, and can go up to 4" an dbeyond if needed.. You basically just need it to be long enough to keep the flow undisrupted. I posted a link to a turbo engineer's explanation (from a tercel forum....I know, credibility lost a couple points there) a couple years back. It's a great read and I'll update this thread if I stumble across it.

EDIT: Here's the thread http://www.saabcentral.com/forums/showthread.php?t=169069&page=2&highlight=conical

Actually we were both posting on this thread as well. De ja vu?
 

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Hi ****

You say "conical" but that doesn't account for the venturi effect. Without venturi, you're reliant upon the turbo to push the exhaust gases out. With venturi (a vacuum in a sense), it drags extra gases out by introducing a high pressure, high flow area... assuming the expansion pipe is 15 degrees.

Don't get me wrong, you're far more qualified than I am to comment... so that's essentially a question rather than a statement. ;ol;
 
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