I bought a 2005 Evo 8 about three months ago. The car had a few bolt-ons, one of which was a DC Sports stainless steal tubular header. About a month ago the header cracked. I took it to a local shop to see what he thought he could do. He suggested welding it. He welded the header while the part was still on the car. About 15 minutes after leaving the shop the car started running really weird and then very quickly developed a knock. I pulled over immediately and shut the car off. I purchased and installed a new header hoping that would solve the problem. It did not. After the install I started it up and the knock was still there but dramatically quitter. I gave it a few revs and it was back to being as loud as it originally was. What could have caused this? What do I do?

 

could be a million things

replacing a header will not fix a knocking engine

take it to a real shop and pull the turbo / header and have them check all the gaskets

put the stock manifold back on as well