How do you know if they need replacing
When they have holes in them, they will start to blow out little white bits of insulation from inside the shielding. Rub a little bit of oil on your oil filter and drive the car for a week or so. If your headers are leaking you will start to find a buildup of little insulation fibers on your oil filter.
As stated above, plus popping and loss of power. Do not wait until it's too late. Mine failed at about 30K miles.
By 20k miles you are on borrowed time...they are probably on the way out with pipes starting to deform and collapse...and only time before they actually crack open.
Replaced mine around 25k . Started to hear what some refer to a ticking sound in the engine bay. Listening a little more, it sounds like a air compressor leak to me.
You also can smell a more acrid exhaust fume. Mine were shot at 13k miles. Just replaced with London QV's... drove much better until the thermo failed 2 weeks later. Related perhaps?? Hope not.
I didnt wait. When I had my engine out service a month ago. I replaced them anyway with Tubi. I just sold the original oem ones and they were in great shape probably because I have been running without cats for a decade. They had about 26,000 miles on them.
They are stock F355 headers. By definition, they need to be replaced. My worry is that the headers may blow and do some other damage before you notice that they're blown. No facts, but I have a theory that blown headers are connected to bad valve guides and bad cylinder walls. I'd rather QV now to lower the probability of an unscheduled total rebuild later. The bomb is ticking. Do you eliminate the bomb now, or wait until it blows up? Pay now, or pay more later? And it will increase your resale value. (Can you guess what my biases are )
