WRX Info

Frequently Asked Questions

Exhaust FAQ: Header

The primary purpose of an aftermarket header on a turbocharged Subaru is to remove or replace the stock exhaust manifold with a better flowing unit.

HP gain is 15HP and 20TQ. This figure is highly debated as different manufacturers use different dynos with different cars with different levels of mods. It also varies because some headers incorporate an uppipe into their design. This makes it nearly impossible to compare the gains of a header without an uppipe vs. a header with an uppipe.

Which manufacturer is best? This topic is highly debated. There have been no reported consistent "bad" headers on the market. Obviously, there may have been bad pipes sold, but not enough to report as "bad" overall.

Who manufactures headers? (Price ranges listed are general, not including sales, specials, etc.)
5Zigen ($500-$999)
alpha werks (<$500)
APS ($500-$999)
Aqua ($1000+)
AVO ($500-$999)
B&B ($500-$999)
Borla (<$500)
BPM ($1000+)
Cusco ($1000+)
DC Sports ($500-$999)
DN Performance ($1000+)
Flatt Racing ($1000+)
Forced Air Technologies (<$500)
Fujitsubo ($500-$999)
Full Race ($1000+)
GP Moto ($500-$999)
GReddy ($500-$999)
Gruppe-S (<$500)
GT Spec (<$500)
HKS ($500-$999)
Invidia ($1000+)
JIC ($1000+)
JUN ($1000+)
Lachaute Performance ($500-$999)
Maxim Works ($1000+)
Megan Racing (<$500)
MRT ($1000+)
Quicktime Performance ($500-$999)
Perrin ($500-$999)
Prosport (<$500)
Skunk2 ($1000+)
Supersprint ($unknown)
SSAutoChrome (<$500)
Syms ($1000+)
Synic Motorsports ($500-$999)
Titek Innovations (<$500)
Tomei ($500-$999)
Vibrant Power (<$500)
XO2Racing (<$500)
XX Tuning (<$500)
ZeroSports ($1000+)

What differences are there with headers? The main difference is exhaust piping length. Headers are made to be unequal length or equal length. Unequal means the piping on the driver's side of the engine will be longer than the passenger's side. Equal means the piping length is equidistant from the engine outlet to the header outlet for all piping.

What about the header comparison? The header comparison idea was started by the NASIOC member downshift1 on this thread and resulted in the publication of the test findings in Speed, Style, & Sound Magazine. An authorized reprint of this article can be found via this link. Larger versions of the dyno plots can be viewed here, here, here, and here. Quite a few headers were tested and the results bring up a lot of interesting data on headers for turbo Subarus.

A newer test was conducted by NASIOC member RainMaker and the results can be found via this link.

What changes will be made to the exhaust sound?
a. Equal length headers: there will be a drastic difference in the exhaust note. It will change from the boxer rumble to a more traditional engine tone. This can be negative for some people as they love the unique sound of a boxer engine.
b. Unequal length headers: there is generally mild to no sound (db) increase or change in tone. Any changes in unequal length headers are generally considered subtle.

I have or soon will have a twin scroll turbo, is that important for header choice decision? Yes. You must use an equal length header specifically designed for a twin scroll turbo, otherwise 100% of the twin scroll turbo's benefits (earlier spool vs. equally sized regular turbo) are gone. While you could use an unequal length or regular equal length header with a twin scrool turbo, you now will have regular turbo spool characteristics or possibly worse.

Which header has the best gains? There is no irrefutable evidence that any header has better gains than another. The consensus, if there is one, is they are all within 5HP or less, gain wise, of each other. That being said, there are extremely wide variations in how each header affects the powerband. This will play a key roll in determining which header best suits your power wants in which powerband.

Are there any downsides to headers? Yes.
a. Some manufacturers' early versions of headers had fitment issues, which could be cause for concern if purchasing a used header.
b. There may be a few manufacturers who still produce headers with possible fitment issues.
c. Increased in turbo spool time. The actual RPM reduction will/may vary with manufacturer/heat wrap or coating/overall header temperature but a good rule of thumb is around a 300 RPM increase (spool comes on later) in spool time.
d. Some newer headers are designed for the STi, so they may require WRX users to use the STi oil pan due to it's different shape.
e. 2006+ saw changes to the placement of the oil filter which can interfere with header fitment, so discuss with your Vendor prior to purchasing headers as to wether they fit correctly or not.

Are there any other benefits from a header? This link contains some very interesting testing of EGT readings from a full exhaust and a header. The results seem to indicate the cause of high EGT readings is due to the poor flow/design of the stock exhaust/exhaust manifold. Though this information isn't 100% foolproof, it offers strong credibility to the thought that headers+exhaust may be the solution to high EGT issues with modified vehicles.

Are there any do it yourself options? Yes. This thread contains a compendium of thoughts and experiences with port matching and port and polishing the stock exhaust manifold. Though there is a lot of theory and speculation there isn't a whole lot of evidence to support this modification having the same impact as a full set of headers. It certainly is a cheap, do it yourself project with few possible negative impacts though. This thread contains DIY porting instructions.

Where do I buy a header? Every Subaru/Import performance store sells headers. For purchasing, support your local economy or the NASIOC Vendors.

What questions should I ask of the retailer or manufacturer before purchasing?
1. Is this header equal or unequal length?
2. Do you provide EGT bung welding? (if applicable to the end user)
3. Do you provide ceramic or other coating services prior to purchase?
4. Does this header include an uppipe?
5. Are there any fitment issues (very important for STi and 2006+ owners)?

How hard is it to install a header? Allow around one hour for install time if using your factory uppipe or have already installed an aftermarket uppipe. Professional installation, depending on your area, is around $75. If using a header with an uppipe, and you still have your factory uppipe, allow around 3 hours for install time. This can depend on many variables. A lift and air tools will significantly speed up the process but aren't entirely necessary. Professional installation, depending on your area, is around $200. Shadetree mechanics will install for around $100.

How do I install a header? Refer to the header manufacturer's instructions.

What about ceramic or other heat wrap coating? Though there are pros and cons to heat retention treatments with exhaust components, the general consensus with headers is that heat retention benefits outweigh the liabilities.
Increased heat retention, which is beneficial for exhaust flow.
Reduces underhood temps, which decreases IC heatsoak.
Additional expense.
Additional lead time, in the case of coatings.
Increased heat retention, which in some cases, can accelerate metal fatigue, especially at weld joints.
No proven HP increase.
If you plan on using a coating, ensure you are aware of what impact this will have on your header warranty if applicable. Coating or wrapping your header can void exhaust component warranties. If using a ceramic-type coating, ensure it's working heat range is above the known EGT. EGTs can be as high as 1400-1600 degrees in the extremes. Some normal coatings are not rated to this temperature level.

What types of ceramic or other heat wrap coating are available? The two most popular manufacturers of heat wrap are Thermo Tec and DEi. The two most popular coating manufacturers are Jet Hot and Swain Tech Coatings. Wrapping is a DIY project with a shorter life span than the professional only coating with a longer life span.

Excellent coating thread
.pdf file on coatings
Car Craft magazine's testing of Jet Hot

Should I reset my ECU after this mod? It is never a bad idea to perform an ECU reset after a mod. The traditional route is to disconnect the negative battery terminal, press the brake pedal for a few seconds to bleed the system of charge, and reattach. Some use the more advanced Vishnu Reset.