When are headers NOT a prob? 1999?

I was on the phone about something else with a well trusted F-chat person and it came up.

 

My manifolds were reinforced at QV London, by the previous owner, but apparently cracked from the inside AGAIN after reinforcing them at their shop. I tried contacting them several times via email but no answer. Subsequently bought a pair of Tubi, works well so far.

 

I have the original headers and valve guides on my 95 355 but I have had the bypass valve removed and replaced with a bypass (challenge) pipe since the car was new. The car has been tracked many times and every time I drive the car it is readlined (many times) .
I have spoken with many people on this topic of valve guides failing and headers failing and the the root cause appears to be the bypass valve either not opening fully or not opening at all. At high rpm this causes massive heat to back up (in street cars) .....and the valve guides go or the headers go or both. When the system fails the bypass valve defaults in the closed position.
I have also spoken with 3 mechanics (2 dealer) and all agree that a cause of header failure/valve guide failure could be a inoperative bypass valve.
There are NO warning lights (at least on the 95 model) to let you know if the system is not working as its supposed to. I re-installed my by-pass valve and for the life of me could not tell if its was opening or not during my test drive although the car seemed to drive perfectly (although a bit quieter). I drove for a 100 klm and then re-installed the challenge bypass pipe and intend to continue to drive the car that way.
Many people seem to condem the car but perhaps they should be checking their bypass valve or better yet remove it all together and install a challenge bypass pipe. As an added bonus the exhaust also has a more aggressive tone (sort of like a tubi).
I wonder if we all removed the bypass valves from day one ........what would be the failure rate of headers and guides?????

 

Taking a guess and thinking your headers are going to be well over that amount?? Or are you guys just not sure on pricing yet>...

 

You cannot remove the bypass valve on 96 and later unless you can spoof the motronic...or it will throw a check engine light and code. On my 1997, you can very readily hear the exhaust "bark" when the valve opens between 3800 and 4000 rpms. There is no doubt when it is working.