I'm having a bit of a dilemma. I have figured out how to produce collectors, now I just need to figure out how to form them to fit a T3 flange. My collectors are 5-1 so I'm not even sure how to make them more rectangular with the angles. Please share any techniques that work without marring up the collector.

 

Insert collector into appropriate pipe (2.5" for T3 usually), draw line around collector, cut around line, and radius flange.

You can also make a paper template and let the long sides hang down further, form in a vice, and then cut and radius. Probably plenty more ways than that as well...

 

I understand how to cut it and what size the opening should be. I'm just seeking tips on going from circular to T3 without destroying the collector.

 

http://spdexhaust.com/pdfs/Temp_Pages/Turbo_CT.pdf

 

I don't want that 16ga transition piece to be a weak point in the collector

 

it is easier to form if it is slightly undersize. fully weld the collector off the flange. line up the flange over the bottom of the collector so that it is as centered as possible. weld the areas where the collector outlet and the flange are very close to the correct size. then use a couple ball peen hammers to shape/stretch the areas that are undersize.