Stainless manifold bolts?
 

Can I use stainless bolts for manifolds? Will they take 35 lbs. of torque, or must I use steel Grade 5/8? Do they make Grade 5/8 stainless bolts?

Thanks in advance,

D. Ocean
Pompano Beach, FLA

i use stainless bolts for my stellings and they seem to work just fine

ARP makes them. They are 10% stronger than grade 8 to hold your manifold in place and beautiful to hold your admiring gaze. Go get em!

The strength of stainless steel is like any steel, there are lots and lots of different alloys with a range of properties. Most common is a 300 series SS. Plus the diameter makes a difference , but I cannot imagine that a stainless bolt would not take the stress of 35 ft-lb. What size bolt is it? I could put lots of dorky equations on here to show you how to calculate the stresses, but I will save everyone the trouble of demonstrating my dorky-ness.

I visited a local bolt supply house yesterday and, according to their charts, a typical S/S 3/8" x 1 1/2" bolt is rated at only 263 in/lbs. of tourqe (21.829 ft/lbs.) That isn't close to 35 ft/lbs that I need for the manifolds.

I'll check with ARP.

D. Ocean
Pompano Beach, FLA

Better double check your info. Way off.

My nut and bolt supply house tells me that I can get grade 8 stainless nuts and bolts... I prefer allen cap screws myself... but you have to spec higher grade bolts than what you get at home depot of OSH hardware..... Some of the high strength stainless alloy bolts won't polish to a high gloss... keep that in mind.. they will be somewhat grey in color.

1 in. pounds = 0.0833333333 feet pounds

263 in. lb x 0.083 = 21.829 ft. lb

???

D. Ocean
Pompano Beach, FLA

make sure apply never seize. reason two dissimular metals.

The guys at my local bolt house just looked at me funny when I asked for grade 8 stainless. "No such thing" was their unanimous reply.

Guess I'll have to contact ARP.

I wouldn't take bolts from HD if they were giving 'em away.

D. Ocean
Pompano Beach, FLA

I have used them on my exaust manifolds and intake for years with no problem's. I use the allen head cap type.just plane old stainless! Oh and my exaust manifold's are stock cast iron 454's, so don't worry!

I've been tempted, but all it takes is one bolt to snap off in the block and my day is ruined!

Maybe I'll try some bolt torque stress-testing on an old block.

D. Ocean
Pompano Beach, FLA

Who needs some foreign import cheap stainless bolts holding their engine parts on. Automotive Racing Products provides the finest in fasteners. Their polished stainless hardware is second to none.
Spend the money, buy the finest. Quality pays, it doesn't cost.

I can share some engineering insight to this discuss, bear with the dork talk. The most common general bolt torque equation is:
Torque= Friction Factor (.2) x Bolt diameter (minor thread)x bolt tension. This relates the torque on the bolt to the tensile it applies to the threads.
The most common stainless steel has a yield strength (where the bolt starts to stretch, not where it fails) of around 40 ,000 psi. A 3/8 - 16 bolt has a minor diameter of around .0310 inch (varies a bit depending on class fit) . So a torque of 35 ft-lb will apply approx 6775 lbs of tensile load on the bolt. That makes the stress in the bolt about 22,000 psi, well under the yield strength of any stainless hardware that is decent. I do agree with you with the HD remark, you never know what you are going to get from those type places. I buy a lot of hardware from Mcmaster Carr. You get it super fast and reasonable costs.

ARP rules. I have 12 point head type. You won't be breaking an ARP bolt off in the head unless you get really overenthusiastic.

Stainless can be made to be very hard and strong. Just think of stainless steel vernier measuring calipers or stainless exhaust valves. I'd go with the arp. People have been severely hurt and killed due to inferior cheap fastners. These things have found their way into nuclear powerplants , heavy industry and lifting mechanisms of all sorts, probably even NASA. I think ARP knows about fasteners and metalurgy and has a good name to live up to. BBB