Doesn’t matter how small the head is, many downpipes just won't have clearance to slip a bolt through.

The issues are generally thermal related. The super strong ARP stuff doesn’t help much. Safety wire them in doesn’t help if they snap when things heat cycle a bunch of times. Inconel studs seem to be the most effective at reducing failures. I just use regular nuts with Nordlock washers. Jet nuts shatter and any other locking nuts I have tried basically loose there locking function with a few sessions worth of heat cycles and they can also make it more difficult to take apart and put back together should you need to service something.

Inconel is key! Two reasons:

1. Retains strength at elevated temperatures (no thermal creep).
2. Coefficient of thermal expansion is almost identical to iron and steel. The torque you put on it cold is the torque it retains at high temp.

No other material fulfills both of the above requirements. Plus, there are many OEM studs and bolts in Inconel available from car manufacturers that are pretty inexpensive.

ARP high-strength steel studs will not hold up to extreme temperatures. For a milder street driven car, they would probably be OK on the turbo to downpipe connection (NOT on the manifold to turbo). On a tracked car or a car making Bob's kind of power, they are a no-go.

I wonder if those nuts are really different than these?

https://www.pegasusautoracing.com/pr...p?Product=MJET

My experience with them was they split in two and fell off in pieces after several hard sessions on the turbo beast. I sure did like the small size hex for installation though.

Great... maybe I'll need to get a friend to follow behind me to pick up the pieces that fall off, like I did when I raced a British car...

Q: When ran chevy's, the rule of thumb for exhaust bolts was "locked and loose". A little leakage was acceptable. A little looseness in the stud assemblies countered the expansion stresses. The locking apparatus held it from rattling off. I wonder if this could also be an exhaust fastener solution for the downpipe attachment?

If you are talking specifically about your car and you are still on the IHI turbo, the downpipe will be a bigger problem than the manifold/turbo. The inconel kits on mine has fixed the problem and I don't tighten them much because I can only get an open wrench on 3 of them. With the mechanical locking, I also don't use any thread locker so the threads are dry and I can back them off with my fingers instead of 1/12th of a turn at a time. The studs themselves have been in place with resbond for 3 years.

so it sounds like your solution is Nordlock washers with inconel studs. I'll need a slightly longer stud to accommodate the washers but I think I have some good ones left over from another project. where did you source inconel studs long enough to accommodate the washers? what type of lock nut should I get? I have minimum clearance on my downpipe

I found these

http://www.fastenal.com/web/products/details/0162564

This type of clamp would be better, actually it's on the rear of my exhaust.
Exhaust Band Clamps, Exhaust Band Clamps, Exhaust Clamps

eBay:
http://stores.ebay.com/Racing-Parts-...9017391&_rdc=1

Nordlocks don't work very well