Is it common for the length of the fasteners, connecting the intake to the exhaust, to vary? I have an 83 single barrel aluminum manifold with the outer bolts at 4 1/2-inch length. I also have a 79 super six, iron manifold but the length of the outer bolts is 4 inches. Is this a normal variance between aluminum and cast iron, or does it vary by year?
I was considering replacing the three fasteners with stainless steel, but I hear that this is not advisable with a cast iron exhaust manifold due to galling and/or seizing. I figure grade 5 steel fasteners would be prone to the same thing plus the corrosion factor. So, what would be the most practical material for fasteners in this application?
-Matt

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-MattMan
LEANED & MEAN

I never checked the length of those bolts, but would not be suprised if it varied by some applications. Most but not all applications had a bracket bolted to the underside of the exhaust manifold, for linkage mounting. In that case the bolts would need to be longer, than if there was no bracket used.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 225 nitrous
64 Valiant Signet
64 Valiant 4dr 170

I think most applications have a bracket bolted on there. For the accelerator cable and kick-down linkage. Both of these applications did.

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-MattMan
LEANED & MEAN

I have a set apart right now and I ran a tap through all the holes and I plan to use Grade 8 bolts and nice coating of never seize on the threads.

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

I would drill out the holes and use the cheapest bolt you can find. So when they rust together, as the inevitably do, you can just break them to get the manifolds apart.

I have used stainless hardware for the last few of those that I had apart. I've had issues with stainless fasteners over the years myself. But not as much trouble with stainless as with regular steel hardware.
There are different grades of stainless.
18-8 is a lower grade, what you want is 316 grade. I spent too much on the last exhaust manifold at a machine shop
as I busted all of the original bolts that hold the flange to the manifold as well as the ones that sandwich the manifolds together. (Yet on the previous one on my son's truck they did the same thing for him for free.... Nother story) both of these were needed when we converted to super 6's.

I wasn't having any luck with drilling them out, kept wanting to go off center. I'd have chucked it and gotten another but I have too much time in gasket matching including the outlet, to chuck it would have meant throwing all of my time away as well.... I get my stainless hardware from mc master carr. I can order today and it will be in my mailbox tomorrow.

No, cheapest is usually cheapest for a reason. If you want steel bolts I'd go no less than grade 5 on these with grade 8 being better.

My point exactly. Drill the hole out and use a cheap 1/4" bolts and nuts to hold the manifolds together.. A cheap bolt is easy to break. Why fight a grade 8 bolt that has rusted together and stainless is overkill. It dosen't take that much torque to hold the manifolds together.

Because the better grade hardware has less chance of breaking in the first place.
How often do you plan on dismantling that joint anyway? They've been together for 40-some years at least. If you think you will be taking it apart in the next 5 or 10 years that by itself (plus a little bit of antiseize) will give you a better shot at disassembly so I'd rather take my chances with better bolts that will have a better chance at actually coming apart instead of breaking
Those aren't meant to be " sacrificial" any chance I won't be drilling them out and fighting them if there ever is a reason for me to have to take them apart once I have them reassembled ..
And the cheaper bolts will have a bigger probability of breaking just from heating up and cooling down than better ones. If you're talking grade 2 to grade 5 or grade 8, in the overall cost-scope of any project in which you'd be Messing with those fasteners ever again, the cost of better ones vs cheap ones is what... Pennies?