I just finished my DIY downpipe and leak tested it by plugging one end and filling it with water. I have a flex joint from Summit welded in.

I was suprised to find that water was slowly seeping through the braided center of the flexjoint. I am not going to worry about it, but should the flex joint be air tight?

 

I imagine it would be pretty difficult to make any braided line that is air tight... unless (like oil/coolant lines) it has a hose inside of it. I'm sure for exhaust flexes that's normal.

 

thats how i check my welds with water.i would think it would leak.i hope not.good luck

 

I wonder if it'll tighten up once it get hot?

 

I wonder if it has a small weep hole like some mufflers do under the braids.

 

The car is running now with no noticable leaks from the flex joint.

Only issue is a leak at the turbo outlet flange, hopefully some ultra copper will fix that. I was in too much of a hurry installing to bother.

The first day I drove to work with no gasket at the mid pipe and it was like running an open downpipe. I think my neighbors must have **** when I first started it up after seeing me working on my car all weekend, cutting and welding and then ending up with this loud monsterous beast. I loaded it up with some RTV sealant (no gasket) and its super quiet now.

 

Rutland makes a 2000 degreee RTV, it's used on stove pipes and such, might work better then the copper. Around here alot of hardware stores stock it, but we also burn cherry and maple trees for heat...

Oh and if anyone is into woodworking, I justed burned a birdseye maple for ya

 

the flex's dont use the braided part to do any sort of sealing. the inside liner does the sealing. its the same design as the stuff you see at autozone for like brake ducts and for some exhaust stuff and intake plumbing. how would you make a flexible section air tight that would handle high heat.. that would not be easy.