I've recently purchased UEL headers, as recommended by MSR.
He led me to believe that UEL was an improvement in top end power and EL is an improvement in mid range power.
Owen just mentioned that it was the other way around?
So can someone please tell me which way it is?
MSR's website has a few paragraphs on UEL vs EL:
Should I upgrade the headers? If so, which type would be best?
The standard headers in your Subaru are a 3-piece unequal length (UEL) type. This is essentially what makes the unmistakable boxer rumble. So if you love the boxer rumble (whoever doesn't is just mad!), stick with the UEL headers. UEL headers work extremely well if you are running a small to medium sized turbocharger. Porting the standard headers slightly also increases turbo spool up and engine response. That being said though, back-to-back testing against equal length (EL) headers showed that although the UEL headers offered slightly more top end power, the EL headers promoted stronger midrange power without compromising top end power too much. However, you do lose the infamous boxer rumble if you decide to run EL headers.
So the verdict is, if you are going to run a small to medium sized turbocharger, stick with the UEL headers. A small to medium turbocharger will spool up quickly with a good turbo-back exhaust system so you won't notice the slight loss of mid-range response when compared to running EL headers. The UEL headers will also promote as much top end power as possible from the small to medium sized turbocharger and you also retain the awesome boxer rumble!
If you are going to run a large sized turbo, EL headers would be recommended to promote quicker spool up for midrange power although you do lose the boxer rumble. The large sized turbocharger with a good turbo-back exhaust system will effectively take care of the slight top end power loss that EL headers tend to have.