I have a greddy stainless steel header 4-2-1. When I put it on I forgot to retighten the bolts between the 4-2. I was at a bad place and the engine was hot so I could not tighten it up to seal the leak. I ended up losing 2 of the 3 nuts holding the downpipe on the the actual exhaust manifold.
It was loud as can be, and I got cocky and hit it up to 65/7k. As soon as I did I realized what I was doing and chilled on it and didn't beat on the car anymore. I fixed the leak and the car sounds normal.
My question is this: Is it possible to mess up anything (exhaust valves) with such low back pressure on a N/A motor such as mine? Again it seems fine, but I'd like to know so I know what to do in the future. Thanks