New headers on 3.2, now 'puffing air' sound. Leak, headstud, ...?

[sid86]

I fitted new headers on my 3.2. Somehow it now seems to make a 'puffing air' sound when idling. Revving it a bit (let's say more than 1500rpm, also when keeping it stable) makes the sound disappear. My first thought is a leak somewhere. My second thought is a broken headstud, but since the car was running fine I don't think this is very likely. It would be very coincidental.

One of the 12 M8 exhaust studs isn't tightening very well. I don't want to torque is any further, because the threads are shredded. This may cause the puffing sound, but I don't see or feel any fumes escaping here.

Some questions:
- When a headstud is broken, is the sound supposed to disappear when revving?
- The threads in the cilinderhead have been damaged. I know about helicoils, but why not drill it with a 7.5mm drill bit and make a new M9 thread? I have one from I believe a VW T2 (M9 cilinderhead side, M8 exhaust side) like this: https://www.vwheritage.com/media/catalog/product/n/0/n0146841_1.jpg

Thanks!

[bkreigsr]

Originally Posted by sid86

....One of the 12 M8 exhaust studs isn't tightening very well....

Question asked and answered in the same post?
Bill K

[sid86]

Originally Posted by bkreigsr

Question asked and answered in the same post?
Bill K

Obviously I’m thinking in this direction, but I don’t know if it is OK to fix with the stud I mentioned. I’ve never read anything about it being used on 911’s...

[sid86]

Just an update for whoever is using the search function in the future:

I removed the headers and cleaned all the ports. There was some old gasket stuff on there. Then I removed the loose M8 stud and drilled it with a 7.5mm drill. After 'tapping' (?) the new M9 thread in there, the VW stud was placed. It works fine and can be torqued appropriately. Lastly I removed both lower valvecovers to check for broken headstuds. All were in place and with a tip of the finger I checked them. After putting everything back together the sound is gone.