Hi all, I've got an 87 GTA with a swapped L98 from a 91 Vette. The car had long tube headers that came with it when I bought it last year. It was a new swap when I got it, put maybe 800km on the car since I got it.

I have an exhaust leak coming from the headers. I've replaced both gaskets already. From what I can tell, the headers are really tight in there and the actual exhaust is rattling under the frame of the car on acceleration. Tried to get it tight to fit proper but it's still rattling.

Any suggestions to find a solution? Not sure how to deal with the leak or how to solve the exhaust rattling. Long tube headers. Wish I didn't have them. I think the leak may also be affecting the idle of the car as when I start it up and it's cold, it runs fine. As things warm up after maybe 5 minutes of driving, I start noticing exhaust coming into the cabin then the car starts to run rough. Thinking it's the O2 sensor.

Thoughts?
Thanks

 

Stick a leaf blower in the tailpipe-tape it in and seal up other exhaust outlets with duct tape. Turn it on and start spraying everything with soapy water. Where the headers hit the frame you have to get out a hammer and dent them in to clear. If they keep hitting the frame they'll crack welds all over-it may already need some welding. To help seal up smaller leaks at the header to head or header to pipe I've used high temp copper sealant with success. Exhaust leaks will give the O2 sensor a false lean, so makes sense it runs poorly.