#2 would be more ideal. Bents in pipes add length longer than the bend. For instance a 2 1/2" 90 ell = 4.2' of straight pipe. 45 bend = 2.1' of staight pipe.

My local auto parts store has 51mm exhaust pipe in ready-bent pieces, including junction pieces. I'm thinking it'd be less hassle to cut and re-weld the collector and add a T-junction afterwards than it would be to make the weird Y-junction piece myself.

Then again, if I hack into the collector I'd have to get yet another post header if I wanted to switch to a single-sided exhaust in the future (which I don't and never will but anyway...).

Furthermore, the 51mm piping is cheap, while the headers may be hard to find in the future and much more expensive. (The one I got now was a bargain and in decent condition, too, but that luck may not last.) So I can afford messing with the piping but if I mod the collector I need to get it right on the first try.

The main question is, seeing as the post 750 header flows supposedly better than the original pre 600 headers, would the performance difference be noticeable?

Very little, it is a Kat after all. What cans are you using? That also counts.

Fake Chinese Akrapovic cans. Straight-through instead of compartment-type. I will be using 51mm piping (the same size as OEM), so hopefully I don't have to rejet, although I'm ready for that, too. Once again, not looking for performance gains.

Also it seems I will have to make the T-junction myself, the ones on sale in the auto parts store have too gentle of a curve so wouldn't clear the centerstand even if I trimmed back the collector.


EDIT:

Pic of T-junction which won't work




Pic of exhaust x2, similar but not the same





EDIT 2:

Pic of the type of T-junction I'd have to make. Not really room for anything fancier. Sucks for flow, but that's why we have the 750 headers and straight-through cans. So the end result would hopefully be more or less stock flow.

Toyota cans? You can use a larger pipe at the T then reduce down for the mid pipes, that will allow even flow and reduce the restriction at that point.

Nah, fake Akrapovics, same cans different stickers, I think those are rebranded to avoid copyright issues.

IIRC the outlet at the collector is 54mm so I gotta use 51mm for that, do you think it'd help if I'd use 57 or 64mm pipe for the horizontal part before going back to 51mm for the rest? The cans are 51mm, too.

Yup, it would act as a collector, balance the exhaust pulses and allow even flow to both cans. I'm thinking 64mm with a 51mm stub welded to it for the header. Don't take my sizes to heart just my thought on the design. You may not even have to mod the header, just move the stub over on the 64mm tube.

The collector outlet is off-center (see photo in first post) so I will have to do the cutting thing anyway if I'm going with T instead of Y-junction.