Guys, I recently purchased a 1972 grand prix with a 400 motor. When I checked out the car before the purchase I knew it had a bad exhaust leak on the passenger rear header gasket and thought no big deal. This weekend when I removed the hedman headers I was surprised to see only 4 bolts holding the headers on. After some internet reading I now know this is common on this year car. Now the questions. I like the headers and the easiest thing would be to re-install them with new gaskets but without the 6 bolts in the flange how long will the gaskets last or am I just wasting time and this will be an ongoing problem. Should I just find a pair of stock exhaust manifolds and repipe the exhaust? I know many have had the same problem. What did you do?......Thanks
If I were you ... and I haven't had this scenario on mine ... I would probably try once doing a new gasket but I would probably get my file down onto the header flange at least, to try to clean it up as best you can. And I would probably use a medium priced gasket along with copper RTV and let it sit overnight before startup.That might leak right away, or not until next year. Maybe never, I don't know. But if you want to keep your existing parts, remove the heads and take them to a competent machinist along with your headers and they can make the holes without charging an arm and a leg. Then you're set. I used to run a pair that had been drilled before I got them but haven't dealt with the issue myself.
I'm afraid that there are no easy answers on this. I love Pontiacs, but that was a pretty stupid move on their part...and they did it on a number of applications. Factory manifolds (being more rigid) are easier to seal, but I've had some difficulty even then. I've only dealt with this on a couple of motors, so maybe someone else knows a good fix. Good luck.