Should I use stover nuts on my SSI's?
 

I think a self locking nut is a good move here. I like stover nuts (slightly ovalized on the last few threads) since they are re-useable and it's a heat resisitant locking device.

Why isn't a washer used under the exhaust stud nuts? Seems like it would reduce the torque necessary to remove them and resultant stud breakage on older units.

Probably a bad idea for already marginal exhaust studs. You have to account for the extra driving torque (enhanced thread friction due to the deformed or ovalized threads) the Stover nut requires when doing the final torquing. Also, this extra torque may be enough more to cause the stud to fail when a future loosening attempt is made, since the extra torque has to be reacted back through the stud to the head as torsional stress. Jim

The factory nuts for the exchangers to the heads are simple M8 nuts and barrel nuts. Both of which are non-locking nuts.

Not sure why locknuts would be needed. It's not like people's exhaust systems are occasionally falling off. Has anyone had this problem?

And i've also considered what Jim stated about the locking problem with age. The nuts are hard enough to get off with age and corrosion. I don't think they're a good idea.

The only locking nuts i've seen on the exhaust are the acorn/deformed thread/stover nuts used for joining the pipe-to-pipe flanges.