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Admiral Ackbar the 1st
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Discussion Starter #1 (Edited)
This seems to be the most commonly asked question. For those who want to research and understand how everything actually works and what all the pluses and minuses are, these questions have all been addressed and a great deal of information is available by searching. Researching each individual component you put on your car is the recommended approach. Beyond that, you must make the final decision and take responsibility for everything you do to your car. This thread is intended to simply summarize the most commonly recommended options and to provide a brief explanation for the reasons.

For the most part, the answer is pretty much the same whoever you ask when discussing 02-07 WRXs and STis. I am not sure what is up with later years, maybe someone else can add any differences.

1) Uppipe: Only required for '02-'05 WRX (no cat in other years/models stock). This is to replace a cat that we have all seen pictures of becoming detached and entering the turbo (bad). Do this first because everything else increases that chance. Very generally 10HP+ and 500 RPM sooner spool is the bonus. PITA to install but cheap to buy.

http://www.clubwrx.net/forums/engine-modifications/134325276-attn-02-05-wrx-owners-importance-uppipe-mod.html

http://www.clubwrx.net/forums/engine-performance/39284-uppipe-downpipe-muffler-install-guide.html

2) Downpipe (bellmouth or divorced wastegate): All years/models. Replaces two restrictive cats. A highflow cat is recommended on 2.5l models to restrict the possibility of boost creep and is my preference on 2.0l. MUST be tuned or used with a stage II map (except '02-'03 some say but do it anyway). Gains are substantial with a tune. Read on boost creep if you have a 2.5l.

http://www.clubwrx.net/forums/engine-modifications/134328228-exhaust-faq.html

3) Engine Management: Opensource reflash, Cobb accessport, or professional tune. Increases your boost safely with fueling and timing adjustments etc. etc. and allows you to run a DP safely. Also very beneficial without a DP (stage I).

4) Catback: This is only for your sound preference. Gains are minimal for the cost. Don't fall into the trap of getting something too loud unless you are sure you like that. Match to the DP for connection - options are 3" flat flange or ~2.5" doughnut (stock)

5) Intercooler hoses: Not that often recommended here but is a great mod for the $. Better flow and maybe reduced temps. - gain is 5hp or 8hp according to the famous author depending where you read.

-1) MBC - Only run these because your tuner recommended. Not a safe way to up boost except very marginally on '02-'03WRX and maybe '04-'05 STi without EM and correct tuning. Engine management is a FAR better option to get more boost and HP on all models. Does not account for extra fueling etc. needed. Issues without tuning include partial throttle full boost, causing bad lean conditions and horrible drivability.

-2) Intake - not necessary yet. May skew your MAF causing you to run lean. If you want one, make sure that it is certified to not mess up your MAF scaling and make sure no one has run into problems or better yet get it tuned. May be a consideration for stage 2 STi.

-3) BOV or Blow off valve: just a noisemaker and not really ideal for your car.

-4) Turbo Timer: Not needed. The turbo is water cooled even after shut-down.

At this point, your biggest gain/$ will be to do your turbo and supporting mods (intercooler, fuel pump, injectors, tune). The most common standard recommendations are 16G EVOIII for 2.0l or 8cm 18g for 2.5l WRX (you are really slacking if you don't research this). Consider an even larger turbo to upgrade the STi.

A variety of other things can be done still though to improve flow, cool the intake charge etc. However, manual boost controllers, intakes and Blow foo valves are not on the list for reasons.

6) Intercooler - STi is already a little better than WRX and can be used to upgrade WRX - small gain little bit cooler charge. High quality big TMIC gives less pressure drop (at least 2 PSI), faster response, less chance of det. and can be tuned for ~15-20hp. Supporting mod for turbo upgrade.

This is pretty much of the top of my head so if you see an error I will correct it.
 

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Admiral Ackbar the 1st
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Discussion Starter #2 (Edited)
Thanks to EJ257 for providing the details for #7-12!!


7) Heat wrap/coatings

Two benefits: increased exhaust velocity by keeping the gases hotter, and reduction of radiant heat into the engine bay (decreased heat soak). Headers / Exhaust manifold, uppipes, and the front half of the downpipe (the rear half doesn't really contribute to heat soak) all would benefit from this modification.

8) Exhaust Manifold P&P, crosspipe.

The inlets are all opened up to make a smoother airflow. Increased exhaust velocity decreases spool time; shifts powerband to the left and power gains are ~10hp/tq. Headers tend to crack over time, but the exhaust manifold is cast iron. While it's off for PnP, if you intend to use an EGT gauge, it's a perfect time to tap the manifold.

9) 3-port BCS - MUST BE TUNED

Allows better boost control, and retains the ECU as the medium for managing boost. [Ron/Jeremy could probably do a better job explaining this one]

10) External Wastegate - MUST BE TUNED

An uppipe with a valve that diverts gases pre-turbo at a specific pressure (based on wastegate spring), which essentially simulates a huge hotside. This allows for more power and better boost control. The two most common sizes are 38mm and 44mm, and can be vented to atmosphere (louder, more efficient) or plumbed back into the downpipe for reduced noise (less efficient). Expect a power increase of ~10+hp/tq. Tuning required for good gains and verify safe boost response.

The EWG FAQ (External Wastegate) - IWSTI.com: Subaru WRX STI Forums

http://forums.nasioc.com/forums/showthread.php?t=2082201

11) Meth/water injection - MUST BE TUNED. High risk if it fails

Two benefits: chemical intercooling and increased octane, which decreases the chance of knock. This allows for the use of more boost, leaner AFRs, and increased timing; power increase is ~20+hp/tq. Failsafe(s) and gauges (Boost / WBO2) are strongly recommended.

12) E85 - MUST BE TUNED

Inexpensive fuel that features increased octane to decrease detonation, and allows for more boost/timing, leading to increased hp/tq. Requires fuel pump and injector upgrade (~30% larger), and not readily available in all areas (see here for availability). Difference between summer and winter blends may require slight modification to the ECU parameters. You should evaluate the potential issues surrounding running this in a non-flex vehicle for yourself but it is well proven on WRX & STi.

The OFFICIAL E85 ARMY THREAD - NASIOC

13) Turbo Inlet - Does not require a tune. Mainly a reliability mod. and increases flow. MANY stock inlets on older cars have ripped - this leads to un-metered air being sucked into the intake after the MAF = lean = bad. Since this is a reliability mod, get something reliable. An "afta-maf" hose (if not included with your intake or inlet) is also highly recommended as sufficient hose clamp tightening to prevent leaks caused mine to crack over time.
 

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Master Baiter
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Good writeup so far, myco :thumbup:

My advice/additions/revisions (your choice whether or not to incorporate them) ...

mycologist said:
Maybe make mention that there are power/spool gains on the 2.5L with aftermarket ones, but not as drastic as the 2.0L (not usually worth it unless upgrading turbos, adding headers that require it, or going EWG).

mycologist said:
2) Downpipe (bellmouth or divorced wastegate): All years/models. Replaces two restrictive cats. A highflow cat is recommended on 2.5l models to reduce the possibility ...
You may want to make mention of the shorty downpipe option (e.g., Bosal) which retains the OEM midpipe cat (which you may or may not gut). This could be beneficial for people in states which require a visual inspection of ECDs.

mycologist said:
3) Engine Management: Opensource reflash, Cobb accessport, or professional tune. Increases your boost safely with fueling and timing adjustments etc. etc. and allows you to run a DP safely. Also very beneficial without a DP (stage I).
OpenECU/AP are the most common, but UTEC is another good EM solution that's often overlooked.

mycologist said:
4) Catback
Maybe link to an adapter like this to allow the use of different flanges.

mycologist said:
-1) MBC - Only run these because your tuner recommended. Not a safe way to up boost except very marginally on '02-'03WRX and maybe '04-'05 STi without EM and correct tuning. Engine management is a FAR better option to get more boost and HP on all models.
Possibly mention the fact that it only addresses boost, rather than boost as well as fueling, timing, etc. which is addressed by EM to give insight why engine management is better than an MBC alone. Maybe mention PTFB issues (though, this may be better in a BCS vs MBC context).

mycologist said:
-2) Intake
At StageII STi power levels, an intake starts becoming a beneficial modification.

mycologist said:
The most common standard recommendations are 16G EVOIII for 2.0l or 8cm TD06 18g for 2.5l (you are really slacking if you don't research this).
I agree on the 2.0L recommendation, but I disagree with the 2.5L one. On a WRX, an 18G is an awesome upgrade, but on an STi, upgrading to an 18G just doesn't make enough sense to justify the $$. Yes, there's more power everywhere on the graph over the VF39/43, but $1000+ worth? Not IMO. Therefore, I think just leaving something about the importance of the 8cm^2 hotside would be better.


That's my $.02 :)

As long as you don't feel I'm stepping on your toes, I'll write some stuff about the other things you mention in your 2nd post to help get this up/ready later this morning.
 

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Admiral Ackbar the 1st
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Discussion Starter #4
Thanks for your input Mathew. :thumbup:

I'll put some of it in esp. the turbo bit. I was trying to keep it very brief but it is great to have all this additional info. in the thread.

Please do write it up I am busy busy today. Thanks!
 

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Admiral Ackbar the 1st
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Discussion Starter #6
@myco: For the uppipe section, providing a follow-up link to my write-up may help keep it short/concise but offer a more in-depth look.
Thanks for the link. I will try to add one or more for each section. :thumbup:
 

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Admiral Ackbar the 1st
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Discussion Starter #7
Thanks whoever stuck this. :)
 

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Admiral Ackbar the 1st
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Discussion Starter #8 (Edited)
Quick brainstorm, that I will probably revise some. I left out driveline bushings - a separate thread would probably be better for that.
Let me know when you are done and I will paste it into the second post and give you full credits.
 

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Friendly Neighborhood Spider-Admin
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Great thread! Don't forget the Shrooms!
 

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Admiral Ackbar the 1st
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Discussion Starter #10
Great thread! Don't forget the Shrooms!
:rotfl: Thanks Ray.

14) Do not eat shrooms that have gills, a white spore print, amyloid spores, and a universal veil. For all others, consult an expert.
 

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Very nice, this should be stickied.
 

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Master Baiter
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mycologist said:
Let me know when you are done and I will paste it into the second post and give you full credits.
I think I've done about all I plan on for now, but I'm not looking for any credit.

mycologist said:
13) Turbo Inlet - Does not require a tune. Mainly a reliability mod. and increases flow. MANY stock inlets on older cars have ripped - this leads to un-metered air being sucked into the intake after the MAF = lean = bad. Since this is a reliability mod, get something reliable.
Do we want to include the post-MAF hose in with this? For ~$75, if you're going to do an intake and turbo inlet, you may as well finish up the intake tract.
 

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Admiral Ackbar the 1st
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Discussion Starter #13
I think I've done about all I plan on for now, but I'm not looking for any credit.



Do we want to include the post-MAF hose in with this? For ~$75, if you're going to do an intake and turbo inlet, you may as well finish up the intake tract.
Yes, I will. I actually had to put one on myself because I had a leak there some time ago and tightened it up stoutly leading to it cracking after a couple of years. It wasn't crazy tight either. That plastic stuff is crap just like the radiator IMO.
 

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Admiral Ackbar the 1st
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Discussion Starter #14 (Edited)
I think I've done about all I plan on for now, but I'm not looking for any credit.
I put the whole list together on the first two posts then. Let me know if you want any edits later.

I made a couple additions to your part and changed it to "spool time" in the manifold section. Please check if that looks okay.

Also, was there any tuning concerns with your EWG - I wasn't sure if it required changing WGDC or anything.
 

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Master Baiter
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I put the whole list together on the first two posts then. Let me know if you want any edits later.

I made a couple additions to your part and changed it to "spool time" in the manifold section. Please check if that looks okay.

Also, was there any tuning concerns with your EWG - I wasn't sure if it required changing WGDC or anything.
Sounds good.

I don't know everything Dom did in my tune (I meant to pull the ROM after the tune to take a peak, but my car went into the shop for 7 weeks directly after the tune and I've been lazy since I got it back), but IIRC my WGDC is lower than IWG setups and set to 0 when the EWG dumps. Our resident ECU experts (Ron/Jeremy) could probably shed some more in-depth input on the tuning aspects.
 

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Admiral Ackbar the 1st
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Discussion Starter #16 (Edited)
Sounds good.

I don't know everything Dom did in my tune (I meant to pull the ROM after the tune to take a peak, but my car went into the shop for 7 weeks directly after the tune and I've been lazy since I got it back), but IIRC my WGDC is lower than IWG setups and set to 0 when the EWG dumps. Our resident ECU experts (Ron/Jeremy) could probably shed some more in-depth input on the tuning aspects.
Okay, let's put requires tuning to err on the side of caution and see what they say.

"Possibly" - great scientific word right there.
 

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Master Baiter
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Okay, let's put requires tuning to err on the side of caution and see what they say.

"Possibly" - great scientific word right there.
It would be safe to say that it requires tuning. If the EWG itself doesn't "require it" (I'm pretty sure it does), it would still be safe to say because I don't think anyone would go that route with the OEM BCS (the extra $100 spent on aftermarket BCS/MBC is a no-brainer). I just can't explain the specifics of EWG tuning, as I don't have that much experience tweaking maps (just minor adjustments to fueling/timing)
 

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Admiral Ackbar the 1st
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Discussion Starter #18 (Edited)
It would be safe to say that it requires tuning. If the EWG itself doesn't "require it" (I'm pretty sure it does), it would still be safe to say because I don't think anyone would go that route with the OEM BCS (the extra $100 spent on aftermarket BCS/MBC is a no-brainer). I just can't explain the specifics of EWG tuning, as I don't have that much experience tweaking maps (just minor adjustments to fueling/timing)
Quick edit - it is in the disclaimer in the FAQ I linked.
 

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Very nice!! Excellent!

For #9 any 3 port run in "interrupt mode" must be returned for as they use 30% less wastegate duty cycle. This means if you slap one on with no tuning and punch it you will severely overboost and probably cause major damage to your engine if not make it go boom. 3-port solenoids allow for better boost control and faster spool when tuned correctly.
 

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Admiral Ackbar the 1st
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Discussion Starter #20
Very nice, this should be stickied.
Thanks!

Very nice!! Excellent!

For #9 any 3 port run in "interrupt mode" must be returned for as they use 30% less wastegate duty cycle. This means if you slap one on with no tuning and punch it you will severely overboost and probably cause major damage to your engine if not make it go boom. 3-port solenoids allow for better boost control and faster spool when tuned correctly.
Sweet, I'll update that. Thanks!
 
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