Grade 8 vs Grade 9 vs ARP?

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I'm not really a believer in ARP's marketing hype. I bought some of their intake manifold chrome-moly bolts for my 302 intake and within a month they rusted. They're supposed to be ultra corrosion resistant
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Anyhow, I need to replace the stock Grade 8 bolts on my TrueTrac that are prone to stretching and cracking.

Will local Lowes/Homedespot/hardware store Grade 8 fasteners do the trick? Or are they cheap copies of Grade 8 fasteners?

McMaster has Grade 9 fasteners with a 170,000 psi min yield strength - the same as ARP.
 
Get bolds at a reputable place. The ones you get at a place like Lowes will probably be of inferior quality. Thread clearance and specs might be bad. In some cases you can't trust markings.
 
Anytime your using hardware around heat you have to keep in mind the stretch or you may find yourself with stripped threads in the heads. Head bolts and exhaust bolts come the mind.
 
I concur with Bob and Al. Fasteners are one case where it pays to make sure you get "made in the USA." Several years ago, there were big problems with defective import fasteners.

Check your yellow pages under "fasteners".
 
The problem is that some fastner companies are selling counterfeit nuts and bolts in real boxes. The point I was trying to make is that bolts and nuts used in hugh temp areas need to expand and contract with whatever they are holding together. Use the wrong head bolts and you could end up with a leaking head gasket, same for exthaust manifolds and headers. Now that we have aluminum and iron mixed together with carbon fiber plastic to make up our engines its even more important.
 
How about McMaster Carr?

They're the only ones that carry Grade 9 (Minimum tensile strength of 180,000 psi) bolts in 3/8"-16 in 1" and 1.5" lengths.

The Detroit TrueTrac differential needs 4 per side to hold in the pinion and side gears. I'm not sure how hot it gets (gear oil?) but the stock Grade 8 bolts stretch and break over time.

I've ruled out cheap hardware store Grade 8 bolts, its too important an application to rely on them.

ARP is rather overpriced and I'm not sure about McMaster's Grade 9 bolts.
 
mcmaster is very reputable/reliable for most of the metal stuff I've bought for work, such as 6061 aluminum being actually that, along with copper, steel, and various other stuff. Never bought *good* fasteners though but see no reason why it would be a problem. Might want to call and have them verify their source for fasteners, let them come out and say they are USA made before you ask if they are USA or Tawain made.

I don't think you're diff. will get over 250F. If it typically does then you'd be aware of it from having the pinion seal leaking from having overheated.
 
forgot to mention, I wouldn't count out ARP. I'm not a fan of marketing hype for anything, but buying from ARP would be more reliable than most other places, including mcmaster for nuts and bolts in my opinion. Their fasteners are beyond grade 8/9/10 quality if that's what you really need.

If you got chrome-moly intake bolts, they are not corrosion resistant. Stainless steel is *ultra* corrosion resistant.
 
They claimed their chrome-moly bolts were ultra corrosion resistant??
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The min tensile strength of ARP bolts for this app. is 170,000 psi.
Grade 9 is 180,000 psi.

I've used ARP bolts before and I'm *satisfied* but they're very pricey and rusted faster than zinc-coated stuff even though they claimed it was corrosion resistant.
 
'Chrome-moly' usually isn't stainless steel so it won't have the same corrosion resistance. Hardenable stainless, which is probably what you'll need for a higher grade fastener, often isn't as corrosion resistant as the more common grades, and all of it is still stain 'less' as opposed to stain 'free'. Strainless is also more brittle than typical tool or alloy steels at the same hardness.

Are you just concerned about cosmetics ?
 
I was a bit peeved about my intake manifold bolts which are leaving rusty streaks on my intake manifold.

For the differential, I'm more concerned about strength overall.
 
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