Looking for a little advice from those of you that installed a header to the stock overpipe. I got a second hand header without any hardware so I’ve bought the necessary gaskets but I have no idea what size/length of bolts I will need to attach the stock overpipe to the header. Can you help with advice as to what you used?

I have UEL catless Gruppe-S +flash with stock everything else. So far I like it. it has the rumble but doesn't drone at all. I would like the rumble to be more pronounced but I'm going to get exhaust at some point for that. for now i really like it.

Here would be my choices
R400
Perrin 2.5
MXP SP/ CSG touring

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Figured I'd add to this thread since I just put my BRZ back to stock and traded it.

I ran a JDL catless UEL header with the corresponding OFT OTS tune for a while. There were no other modifications on the car (i.e., the rest of the exhaust was stock). I also made the JDL specific valve timing changes that I found on the forum to the tune.

Overall, I liked it. The car was legit faster in almost any scenario. It turned the original three part powerband (initial torque hit, dip, then torque's back...) into a two part powerband with a low and high end. Though, I swear the car lost torque between 2K and 2.5K rpm.

Regarding sound, I can see why some might not like it. It had a bit of a nasal quality to it. Overall, I was cool with it. If I were to do it again, I might go equal length, I'm not sure the uel rumble thing is for me. Regarding volume, a lot of people say it barely increases volume. I'd say it notably increases volume but it isn't too loud. I wouldn't want it any louder, but then again I'm a pretty understated person and like to exercise a vehicle without alerting everyone or drawing attention.

UEL and EL have different sound profiles because of changes in pressure pulse timing. EL is definitely quieter than UEL.