exhaust manifold stud material

[broken22]

I am going to change the turbo on my car soon and gave decided to replace all the exhaust manifold studs/nuts soon.

What grade and material metal is best suited to a turbo high heat appliaction?

What does OEM use?

[Z2TT]

OEM Probably are mild steel.

A good choice to use is ARP Bolts. Their exhaust bolts are made of stainless steel.

http://www.arp-bolts.com

[oldcorollas]

mild steel?
bolts are never "just" mild steel. (except those shitty ones you get at bunnings with no ratings)

[Z2TT]

Thats the closest description without knowing the exact composition I guess.

[LeeRoy]

If you don't decide to go genuine or performance studs then just swing in to your local bolt shop ie Lee Brothers aka 'the nut house' in north parramatta. Much cheaper than genuine for what is essentially the same thing. The only difference is often the size of the head with genuine often having 14mm whereas the same bolt would have 17mm, not relevant to studs but just a heads up.

[oldcorollas]

Thats the closest description without knowing the exact composition I guess.

in this case, it is very dangerous to "just guess" at what type it is, without actually knowing anything about it. it is better to not make any suggestion, if you are not 100% sure of the answer.

eg, the difference in strength between "mild steel" and a high tensile bolt could be 4 or 5 times!...

[Hen]

Many years ago I had a hell of a time finding anything to replace my exhaust studs with. Now I know a trip to Pick-a-part will probably get you anything you need, but back then I ended up buying a metre of all-thread from a bolt place. I then cut it to length as needed and used it as studs. A bit annoying since it had no smooth bit in the middle to grip, but it worked, and a metre lasted for years.

Hen

PS, Bolts and studs != mild steel

[crowncustom]

High tensile is the best to use for manifold bolts especially exhaust as high tensile will take more heat and wont be prone to stripping threads and breaking.
Cheers Brett.

[legend]

thinking of brass for mine

[timbosaurus]

I've always used standard high tensil bolts without issues. The important thing I have found with turbo's, is to use the right nuts on them.

If the engine is rigidly mounted, or not the smoothest running engine, normal nuts will shake of REALLY quickly.

Spring washers loose their spring with the turbo heat.

Nylock nuts loose their nylon bits.

The best option i've found is to source "castle" nuts from a fastener shop, as apparently that's what's on most OEM turbos.

If anyone else has any suggestions, i'm all ears.

[the_random_hero]

All we use is standard high tensile bolts/studs and have rarely had a problem with them. Breaking OEM studs is pretty common on older cars, however.

[IN 05 NT]

toyota manifold nuts/thread pitch is the sam across the entire range, swing past any exhaust shop and they will have studs and nuts on the shelf....we are always using them as with any manifold change....as one will usually break.

[LeeRoy]

The best option i've found is to source "castle" nuts from a fastener shop, as apparently that's what's on most OEM turbos.

On my exhaust manifold it had cone locks and normal studs holding it on.

When I was undoing it they were that tight on the studs that out of the 4 nuts I had to undo it sheared every one of the studs off, or totally stripped the stud clean of any thread. Not sure if these are the same as what your talking about. On everything else youve said im in 100% agreeance.

[mrshin]

Steer clear of stainless, or any high grade stuff - they always end in tears furher down the track. I use plently of mild steel exhaust studs every day - for installing manifolds, turbos, extractors, whatever - and they always give the least trouble to remove again later. Make sure the threads are in top shape before you stick a stud in there, and put a little coppercoat on them.

[Z2TT]

Steer clear of stainless, or any high grade stuff - they always end in tears furher down the track. I use plently of mild steel exhaust studs every day - for installing manifolds, turbos, extractors, whatever - and they always give the least trouble to remove again later. Make sure the threads are in top shape before you stick a stud in there, and put a little coppercoat on them.

Would that mean ARP exhaust bolts would be no good?

[Lambolica]

Factory Studs would be 8.8 Grade, you can go up 10.9 or 12.9, but there is no way living that an exhaust manifold stud is going to fail even at 8.8.

OC: correct me if I'm wrong but the higher grades would be more prone to shear failure? less ductile and more brittle?

Cheers
Simon

[oldcorollas]

at higher temp, all grades will reduce strength.. if you start with a weak bolt, then it might stretch once it gets hot (depends how hot we are talking tho)
they might be more prone to fatigue failure, but not many bolts have high enough forces on them to shear (sideways)

if you look at this (very general) guide, you will see that only the shittest of shit bolts are mild steel (low carbon steel).. ie grade 2.
http://www.boltdepot.com/fastener-in...ade-Chart.aspx
then again, here it has up to grade 5 as low carbon http://www.engineersedge.com/hex_bol...tification.htm

i would suspect that something like 8.8 (or any high tensile bolt) will be so underloaded, that they would not fail, even with fatigue loading.
more of an issue is corrosion and nut sticking.. steel and steel will rust, but staino will also stick together.
at least on old rollas, they still used brass nuts but i'm sure they are not strong enough for turbo application..

i don' thave anything calibrated enough to check the carbon content accurately, but i could do hardness tests or check microstructure


ductile vs brittle... if you have ever overtorqued a head bolt to failure, that is sudden brittle fracture. (with a bang)
whereas if you get some galvanised or bright bolts from the bunnings shelf, and overtorque them, they will twist and stretch and slowly fail (like licquorice)... you really need to load up or abuse a high strength bolt to get it to fail...

[Lambolica]

Or get a poorly made bolt.

Most failures on exhaust stud would be from actually trying to remove a nut off a seized stud (or Torsion failure / Shear failure). I'm yet to hear of a tension failure.

So my question would be: what does the cycling of heat do to the higher tensile strength bolts in that they fail after many years in torsion? surely the temps in an N/A manifold/head don't get to the point of altering the crystalline structure of an 8.8 bolt?

Cheers
Simon

[Draven]

but i'm sure they are not strong enough for turbo application..

Quoted for truth.

I munted a variety of brass bolts before going cone locks on high tensile studs. no issues since
(on dump pipe I'm talking, but similar temps to manifold)

[broken22]

Thanks for the input so far guys.
I might price up some OEM studs/nuts.
Has anyone used titanium nuts on steels studs, theory is they expand at different rates so dont come loose.