Soft or hard bolts for exhaust flange?

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cudajim

cudajim

cudajim
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I have a stock 225 6 cylinder exhaust on my 67 fish. I'm wondering if I should use hardened bolts for the exhaust flange or go with non-hardened ones.
 
Are these studs or through bolts? (Not a slant guy, me) If through bolts, I like to use grade 2. That way if they seize, you have a chance at just twisting them off and replace.

I'm not sure it's a good/ bad idea, but years ago, I used to use brass nuts on studs.
 
I've always been told grade 8 will not rust as quick, and heat will not harm it like grade 1-2 bolts
 
For exhaust use hardened. Minimum grade five, preferred grade 8.
 
I use grade 8 bolts with brass nuts.
 
See no point in G8's for exhaust. Been using G5's or SST with brass nuts for over 15 years. Never had one come loose when it shouldn't have (one system has ~30k punishing off-road miles on it), and never had one not come loose when I wanted it to. Never had one strip, gall, or seize either.

FWIW I build all of my own exhaust systems and I build them with flanges so that they can come out in sections as needed for other work. As an example the system under the Valiant has a flanged connection at the head-pipe to mid-pipe, mid-pipe to muffler, muffler to tail-pipe, and tail-pipe to resonator, so 4 flanged junctions with 3 bolts each.

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Personally, I use grade 8 on everything vehicle related. I found a surplus place near me that sells them by the pound, super cheap. That's just me though, I like overkill and I tend to break bolts under grade 5.

For the flange, I don't see a need for brass nuts. I DO like to use them on the studs at the head though.
 
I can see using G8's exclusively so that you know that's all that ever can get used. Eliminates accidental use of a lower grade where its important that a G8 be used. But if a guy is going to have to buy them specifically for this application and isn't buying more for stock I don't see the need for the extra strength and expense. Fine if you want to do it, but not necessary.

I've had to replace just enough exhaust manifold studs because of galling to exclusively use brass nuts there too. When I first used them I was paranoid about them not doing the job. That's not a worry anymore and hasn't been for more than a decade.
 
I agree with ntsqd above. ESPECIALLY if you are using through-- bolts in the flanges as he's pictured, if one of those seizes up, grade 8 just makes it impossible to remove. At least with grade 2/ 5 you have a chance at twisting the bolt off and then it just falls out.

Hell the bolts in my Hedmans (coming off) collectors are 3/8!!!! Grade 2 would be plenty strong
 
ntsqd said:
I can see using G8's exclusively so that you know that's all that ever can get used. Eliminates accidental use of a lower grade where its important that a G8 be used. But if a guy is going to have to buy them specifically for this application and isn't buying more for stock I don't see the need for the extra strength and expense. Fine if you want to do it, but not necessary.

I've had to replace just enough exhaust manifold studs because of galling to exclusively use brass nuts there too. When I first used them I was paranoid about them not doing the job. That's not a worry anymore and hasn't been for more than a decade.
Click to expand...

Completely agree. I was a bit paranoid about the brass nuts too, but they're nice on slant exhaust/intake studs since you're more likely to strip them than over-tighten them and warp the exhaust/intake which is of concern with slants.
 
I use grade 8 with anti-seize. Worked on too many Chevies back in the day. Always breaking hardware or hardware rounding off. Not on my cars...
 
I tell you what breaks exhaust bolts and studs off worse than anything I ever saw. New cars. From like 1990 on up. I think they were made to be put on one direction one time. When I worked for Toyota, we dreaded doin anything requiring removing the head pipes from the manifolds cause they always broke. You can even see how the nuts are serrated on the ends to grab the stud when you try to loosen it. GHEY.
 
Grade 8, do not over torque, just enough to tesion the bolt. About 15 ft-lbs for 5/16" bolts. Manifolds expand, and slip some on the heads, especially at the ends. To much can break bolts. That is why most manifolds did not have gaskets. But with headers, most need gaskets.
 
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