Is the test pipe suppose to be the same size as the cat back or is it suppose to be the same size as the collector? for example dc 4-1 header 2.25 collector and cat back 2.5. Do you need the test pipe that is 2.25 or a 2.5?

 

They can make it fit. It's not that hard. It would just bug me to know they were different sizes. But they will just weld it. No big deal.

 

I made mine the same size as my cat-back, which will eventually be the same size as my collector.


You've already got your collector restriction, why add another?

 

thats where my problem is i made my test pipe the same as my cat back which is 2.5 but the header i have doesn't have a 2.5 collector cause it's not jdm it's just a usdm dc 4-1 and the donut gasket i bought fits the collector perfect but the test pipe is just a tad bit bigger and now it's leaking. i just need to find the right gasket for it to stop leaking. gasket between usdm dc 4-1 header and 2.5 test pipe....