Why do WRX and STi owners switch to an equal length header?

[Alin]

What is the purpose of this?

 

[Piratemosh666]

Better spool, better torque production, etc. and a few others I'm forgetting. Most of all is because it equalizes the power pulses from each cylinder and reduces EGTs from the cylinders that are most prone to high EGTs. That "boxer rumble" that some of us love so much is actually the sound of inefficiency.

 

[Alin]

Then why did Subaru start with UEL headers and why do they continue to produce cars with UEL to this day?

 

[Piratemosh666]

Packaging constraints and emissions requirements. The OEMs have a lot of compromise to work through.

The FA20 in the '15 WRX has a low mount turbo and because of the packaging, uses an EL manifold.

 

[Alin]

I see highly built STi's with both UEL and EL headers. Wouldn't it be more or less based off of the tune and other supporting mods?

Now you say: "The OEMs have a lot of compromise to work through."

Are you referring to the OEM headers? In other words, meaning that aftermarket UEL headers would solve issues?

 

[Piratemosh666]

Every header design has a thought and purpose behind it (I hope anyway). It may be low end/spool, high end power, or gains throughout the entire range. As you were asuming, the huge variable here is also the tune to go with the header.

Small volume may pressurize quicker, but the UEL design will have worse engine VE (Volumetric Efficiency) characteristics and turbine efficiency beyond low to mid range. There's always a trade off.

 

[Batmobile_Engage]

Now you say: "The OEMs have a lot of compromise to work through."

Are you referring to the OEM headers?

I think he's referring to the OEMs (companies) having to comply with stringent emissions standards.

Also, engineers often are stuck trying to find the cheapest option, which is forced by company leadership to meet a price point.

 

[Piratemosh666]

Yes. You hit what I was trying to get across.

 

[eric.marsh]

I'm running stock Equal Length headers. Initially I wasnt a fan of the sound. Lets face it, the classic "subaru rumble" is awesome. However the sound has grown on me quite a bit! It kind of sounds like an Evo/Honda on the inside of the car, however it retains a slight rumble. As performance, it would be interesting to put on some oem unequal lengths to see the difference in spool.

 

[Grinder34]

I believe all the fastest OEM versions (like RA-R) use EL. Its just better for all the reasons listed above, except for "sound." You can sure tune an UEL header, but if money's no option I'd always opt for EL.