For tubular headers? ...Far as I know, there ain't none - that work.
The point is to get them on "just enough"...just enough to seal out any leaks, but loose enough not to crush the gasket (if you use one) or distort, bend the flange.
You have to take into account heat expansion, vibration, long term temperature cycling, in other words, all the reasons car manufacturers had resisted using them on production cars for all these years; obviously cast manifolds are much more dimensionally stable under heat than tubular headers...thus less issue with leaks, less problems with routine maintenance.
My method: is to us a short handled box wrench or 1/4 inch drive ratchet to tighten them down the first time. (Unless you have Pop-Eye arms...that keeps the torque down to about 30 ft/lb). Then fire it up, listen for leaks, tighten down just enough to stop any leak. Let it run for 15 - 20 minutes. Then let them cool down, over night if you are not in a hurry...then fire it up again, tighten down until any new leaks are sealed.
That usually takes care of the sealing them. You may want to keep an ear out over the next month or so, just in case. Unless you hit something in the road or some grease monkey starts hanging off you exhaust system while its up on a rack - that should take care of the problem.
Since header bolts are usually in inaccessible places, it isn’t easy to use a torque wrench (or get good readings). Be advised or recall, if you use an extension or articulated adapters...the readings are no longer true, you need to factor in a variance for the additional mechanical advantage of each extension from the drive head ... most people either don't know that or care, but it will cause the reading to be off.
With that in mind, giving a torque figure is just about useless...results is what matters. that’s why I use the ear as my torque meter.
Another thing to remember - Better quality, thick flange, headers are like money in the bank.
<font size=-1>[ This Message was edited by: Beoweolf on 3/26/06 9:22pm ]</font>