Welcome to the North American Subaru Impreza Owners Club Friday November 24, 2017
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
Go Back   NASIOC > NASIOC General > Newbies & FAQs

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads. 
Thread Tools Display Modes
Prev Previous Post   Next Post Next
Old 08-15-2008, 01:30 PM   #1
Defiant Autospeed
Member#: 155450
Join Date: Jul 2007
Location: Austin/Beverly 2 of us now!
2007 FXT

Default General Subie Newbie FAQ. Lets answer a few common questions and dispell some myths.

Tired of seeing all the bad info, same questions over and over, and SO many misconceptions. So here are some things to read up on.

This wont be anywhere near complete in its first version, so check back regularly as it will surely see a lot of updates.
This also will be in no particular order, and I am thinking that as it gets more extensive, I will break it down into categories.

I would have done this on my personal screen name, but its in Timeout right now , and half the time I post in here, I am on this screen name anyway.

Stock up pipes with a cat. What years have them?
---- 02-05 WRX, 04-05 Forester XT.
Do I really need to get rid of it?
--- YES. Its a big reliability risk, they are known to melt and shatter into the turbo. Which in 99.9% of cases, destroys the turbo. They also cost you a lot of performance, especially so on modified cars. That cat slows down spool and chokes the engine. This costs you a good chunk of low end power, including off boost power around town. Not only the low end TQ, but overall TQ across the entire powerband is affected. 15+wtq is not an uncommon gain when going to a catless up pipe.

3. I already have a catless up pipe stock, or I can buy a stock STI up pipe cheap, isnt that as good as aftermarket?

--- Yes and no. It will outflow the oem catted up by a lot, but it cant hold a candle to a good aftermarket up pipe. The OEM catless up pipe is small, and the bend is HORRIBLE, resulting in a big chokedown point. Gains are still in question as to the extent, but they are definately real, especially so if you port the turbo. If you have the money, its definately worth doing. maybe not as the first thing you replace (if you already have an OEM catless up), but it should be on your list of things to do at some point when you are at "stage 2" or above.

Do I want a Flex up pipe or solid?

--- I personally always tell people to go flex, and over the years flex up pipes have been shown to have less occurances of leaks at the lower flange. The OEM pipe has a flex, what does that tell you. However there are some very well designed solid up pipes, and many report no problems with them. Personally, I think flex is the way to go, Subaru thinks so too. In the end, its a personal choice.

I want a atmospheric venting BOV, but I heard they are bad and make you run rich?
--- first off, they DO NOT make you "run rich" When you are driving around on the throttle, even lightly, and at idle, they are closed just like stock, so you arent going to run any different than you would with a stock valve.
The rich condition that you DO get, is when it vents. However, this problem is WAY overblown, as its only for a split second, and you dont go THAT rich. Typically about 1.5-2 points, which is no big deal. Its for such a short period of time that unless you are a GOOD driver doing track events, you likely dont shift fast enough for that small drop in power to really change your times anyway. Same goes for the drag strip, most people dont shift fast and smooth enough to have any negative affects. Most people that report a stumble at the drag strip are getting that stumble as a result of a poorly done shift be it with the lever or their clutch foot. Of course SOME people are good enough, and those should stay recirculated.

But I can tune for the BOV right?
--- There is no way to tune out the rich spot after you shift.

Then I should just run a 50/50 style valve
--- Why? You will still go a bit rich. If you want the noise, have the noise. If you want a little noise, do an intake That is how I see that statement anyway.

So if rich isnt an issue, why shouldnt everyone run an atmo BOV?
--- Because many MANY of them leak. Some because almost no one takes the time to set their valve up properly, some because of poor design. Suffice it to say that a manufacturer claiming that their valve will hold 30PSI, doesnt mean that it will hold even 10 reliably. Some of the most popular aftermarket BOVs are also the worst offenders. Others are rock solid.

Mine isnt leaking and I have had it for years
--- If you are going on the fact that you are still at the same boost level, you cant say it isnt leaking. A leaking valve, unless its a BAD leak, will only bleed off a little pressure, the ECU shoots for a specific boost value, if the valve is leaking, it will simply change the wastegate duty cycle to compensate to keep the boost at the target value.

So if I am making the same boost, what does it matter?
--- Because your turbo is now working harder to get there. A harder working turbo=a less efficient turbo, which= hotter air charge. This is bad for power for 2 reasons. 1. Hotter air is less dense and will explode with less force. 2. Hotter air is more prone to detonation. Even with a good intercooler, hotter air IN=hotter air out.

But rich is bad for the cats!

--- Yes, but 3/4 of the people who run atmo valves are catless anyway And again, its such a short time period, and isnt THAT rich, that the chances of you causing a premature failure of your cat/cats is pretty slim. However, if you have a catted up pipe, stay away from atmo bovs, as even though they dont add that much danger to the cat, that cat is already dangerous enough on its own. Dont make a bad situation worse.

I heard cold air intakes (CAIs) make you run lean and you have to tune for them. Is this true?

--- Yes and no. The mindset of all cais are bad comes from a time in the early 02 to mid 04 time period when pretty much all of the available CAIs were poorly designed and caused problems. However, a constant lean condition from these intakes was VERY rare, as the larger problem was rough airflow over the MAF.

So can I run an intake safely and without tuning?
--- If you get a well designed intake you can. There are several that work well. What you want to look for is an intake with the proper sized MAF housing, and no big huge bends right in front of the MAF. The less bends in general, the better, but in cais there have to be bends, so smoother and farther away from the MAF is what you want to look for. Some of the ones that are known work well include the SPT short ram w/heatsheild, the Cobb short ram with heatsheild, the APS 65mm cai, the K&N Typhoon short ram w/heatsheild, the new style AEM cai, as well as the Prodrive CAI. There are others out there, but I am not going to go into a huge list, I just wanted to give some examples. No I am not only recommending what I sell.

Short ram or CAI?

--- In general short rams will outflow a CAI, but you need proper heatsheilding or it simply becomes a hot air intake. If possible, pick a CAI over a short ram. But be careful in your choice. And if you do a short ram, make sure it is sheilded, the more isolated from the main engine bay, the better.

What about the danger of sucking water up with a CAI?
-- Yeah that is possible, but unless you like to go around fording streams, you shouldnt have a problem. stay out of water that is more than 3-4" deep, and dont BLAST through it, and you should never have a problem.

What about things like AEMs CAI safety valve thing?
You dont want it on a turbocharged subbie. You pull enough air through the intake with enough force that you will suck it open every time you go into boost hard, getting unfiltered air into the engine.

Should I do a bigmaf/APS70mm/whatever larger than stock MAF intake?
--- If you are going to a 20G or larger, yes its highly recommended. If you THINK you may be going that large in the future, and you are planning on getting tuned right now, you may as well do the larger intake now. But remember, tuning for the larger than stock MAF intake is absolutely essential.

I heard that you should do a VF43 instead of a VF39 because the VF39s all crack, creep and spike.
--- While its certainly true that the VF43 doesnt crack as often, or spike and creep as often, they do still have all 3 problems. They definately dont crack anywhere near as often, but they do sometimes still crack. And they creep pretty much just as often. Its a problem inherant to the IHI exhaust housing internal design, and as such, its a mechanical problem, that the only REAL fix, is porting work to reshape the wastegate passage entry.

I heard the VF43 is bigger/has a larger wastegate passage/differently shaped wastegate.
--- Not true. The exhaust housing on the VF43 is identical to the VF39. The WG passage is identical in every way, same size, same shape, same shape on the entry into the passage. The difference is that on the VF43, the wastegate actuator is stronger, to help curb creep. It works, a little

But the VF43 is bigger than the VF39
--- Nope. Took them apart and measured them, and closely examined the blades/wheels side by side. Other than the Wg actuator and external shape of the compressor housing(which has no bearing on performance), they are identical.

So porting=fixing the wastegate?
--- This is again, a yes and no question. Technically when done correctly, you arent porting the wastegate, as much as reshaping the entry into the passage. I wont go into detail here, but you NEVER open the hole up larger, just smooth the leading edge and reshape the entry a bit. A real port/polish also fixes the horrific mismatch of the size of the up pipe outlet to the turbo hot side entrance.

Last edited by Defiant Autospeed; 08-15-2008 at 06:04 PM.
Defiant Autospeed is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
BOV FAQ: The REAL dirt on BOVs. Ups AND downs. Lets dispell some myths. Davenow Newbies & FAQs 804 10-17-2017 03:59 AM
please help me answer a few AP questions about doing a turbo njhxc27 AccessPort 3 05-05-2010 03:12 AM
Dispell the myth. RS and WRX wheels are the same for the 05 but.... 3DF Tire & Wheel 10 07-07-2005 10:34 PM
Questions and Need Some Help impr25rs Brakes, Steering & Suspension 2 05-31-2004 12:48 AM
Bay Area WRXers - Questions and maybe some Help!? lionfish42 Bay Area Impreza Club Forum -- BAIC 20 01-09-2004 05:45 PM

All times are GMT -4. The time now is 07:01 PM.

Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2017 Axivo Inc.
Copyright ©1999 - 2017, North American Subaru Impreza Owners Club, Inc.