And then there is this. I have just been down the same hole, and came across this thread.

https://forums.pelicanparts.com/porsche-911-technical-forum/1115709-arp-head-stud-torque.html
How do you make sense of all this?
Alan

My own take, as an engineer: The torque spec Porsche gave for its steel studs is enough to keep the heads clamped tightly on the cylinders. More than that is nice, but not necessary. The ARP studs can go higher yet, but presumably ARP has done their engineering and testing to justify even more torque. Thus, a value above the Porsche spec, but not more than the ARP spec, "should" work.

The downside, as mentioned in that other thread, is that higher torque will cause more distortion of the heads and cylinders, and case. possibly causing pulled case threads. Judging from the structure of those parts, I don't think that is a big problem; and I have not heard of anyone running ARP studs to have had problems using their spec torque. So it's probably not an issue either way. I like the compromise that ARP offered of 28 lb-ft.

But, what I would really like to see is ARP make their studs thinner, so that they are "stretchier" to accommodate the growth of the engine without increasing clamping force as much due to that growth, and then reduce their spec to 28.

That makes a whole lot of sense.
I finally settled on 28 after going thru these threads. The problem, for me is I have 2 other heads which I can't remember what I torqued to. Since I had just removed one head. But there is no cam binding and I may well have decided on 28 previously. Whatever the value I used before they are performing just fine so was reluctant to break the torque on them. If I don't have cam binding even if some are at 28 and some at 38 I suspect I will still be OK. Each head doesn't know what the other has. Just the cam box.
Alan

Are you sure about all of this? Clamping force is about stretch and depends on the material being stretched, no? Some material would require more stretch that others. Just like Porsche has specs for rod bolts that vary, depending on the material, but same diameter and length.... Do people torque ARP rod bolts to the Porsche rod bolt spec, or do they/should they follow what ARP says? Why would head studs be any different? Have not used Supertech head studs, so not familiar with the torque spec. Is it the same as Porsche or different?

Use what the manufacturer of the bolt/stud states, unless you can prove a different method would yield better results...

Cheers

1. The material in both the Porsche and ARP studs is high carbon alloy steel. Nearly all carbon steel alloys have the same Modulus of Elasticity (about 29Msi/200GPa).
2. The Porsche and ARP studs use the same thread size and pitch (helix angle), as do the Supertec studs. Therefore, X ft-lbs of torque on any of them creates the same clamping force (assuming they are both lubricated and tightened the same way).

The 3.0 and later aluminum cases can take much more force than the magnesium cases, therefore, I would be less concerned about increasing the torque on the studs in those cases. However, I would not exceed the Porsche spec by much in a magnesium case, even if it has had case savers installed.

You have built more of these engines than I have so you have more practical experience than I do. if the engines you put together don't pull studs or have other problems related to higher stud torque and component distortion, then keep doing what works for you. I don't know what the Supertec studs torque spec is. Does anyone else?

Do all available studs have rolled or cut threads?

Rolled.

" I don't know what the Supertec studs torque spec is. Does anyone else?"

Found in archives
Alan
tourque spec (+ and - 2lb standard tourque pattern is maintained
a. 2.0 ally case = 30lbs
b. 2.0,2.2,2.4,2.7 (all mag cases)= 28lbs
c. 3.0, 3.2,3.6 ally case =30lbs
d. 3.0, 3.3,3.6 ally case turbo= 35lbs

Had not considered the Mg case motors as we always use OE steel studs on those.

However, It would be intersting to see what the different materials are (despite all being High Carbon Alloy Steel) between Factory, ARP. Canyon, Raceware, Supertech etc that makes their in house engineers come up with a different torque spec.

Interested from a learning perspective. I would acutally like to know. Maybe Henry will chime in, as someone who went down the path of contracting the engineering of a head stud.

Cheers

It's not only the alloy, but the forming of the stud and heat treating that affect the strength. The ARP stud is an austenitic alloy, so to develop maximum strength, the heat treatment is very important. From ARP's web site:

"ARP only uses premium grade 8740 alloy and a proprietary ARP2000® alloy that are rated far superior to “aircraft”quality alloy steels. Secondly, each stud is placed vertically into special racks and precisely heat-treated to 190,000 psi for the 8740 material and 220,000 psi for the ARP2000® material."

https://arpstore.com/products/cylinder-head-stud-kit-for-porsche-2-0l-3-8l-air-cooled-engines-911-930-turbo-premium-austenit

The other vendors almost certainly use the same 8740 or extremely similar steel alloys

Pushing this discussion a little further: If I were engineering the studs, I would use the same alloys but I would make the studs thinner. If the ARP studs are good for a torque of 38 ft-lbs, and 24 ft-lbs is sufficient to hold the head on the cylinders, then the ARP studs are 58% stronger than they need to be. Therefore, I would design them to be 36% thinner in cross section than the ARP studs. This would make the studs "stretchier" by the same 36%. When the engine grows due to reaching operating temperature, those studs are stretched by the growth of the heads and cylinders. That increases the stress in the studs, which increases the pulling force on the threads in the case (and the head nuts, but those never pull out because they are steel too). If the studs were thinner, they would not create as much force on the case threads as they stretch. Therefore, the cases should resist thread pulling and case distortion better.

Thus, "weaker" studs would build a "stronger" engine.

What I am curious about is the fact that Porsche say 23 ftlb is enough for my 930 heads.
So why would other stud suppliers decide they need up to 38 ftlb to tie down the same heads - esp if they are using basically similar materials.
Alan

I guess if the factory torque specs "are sufficient" and the studs are fine. Why the aftermarket head studs????

There are some assumptions being made the the factory torque on thier studs is sufficient, and that it should apply to all studs....

Again, approaching this from a learning perspective.....

Like I said earlier regarding rod bolts.... Sure same basic material, but why higher torque? Even Porsche dramatically changed the torque spec on those bolts with a slight change in material that likely fell into the "same class" of material...

Lets keep the discussion going so we can all get more info.

Cheers

Jeff, fair question. Many people who build race engines believe they have to use the "best" of everything. That ain't necessarily so.

Why? You would have to ask ARP. Like a lot of things sold under the "performance" labels, marketing is a significant part of the game, because in a lot of customers' minds, "more is better." Racers are notoriously susceptible to this line of thinking. They see someone else winning races and see that they use certain parts (suspension, engine, aero, tires, wheels, anything else) and they want the same things. The companies that make these parts are all to happy to oblige. In reality, they just aren't as good drivers as the fast guys with names like Hamilton and Verstappen. :cool:

When Porsche came up with the 24 ft-lbs torque spec for the SC engines (including turbos!), and subsequent X ft-lbs + additional angle spec, they added some factor of safety to allow for unusual cylinder pressures due to detonation, some deformation of the case, cylinders and heads, etc. Thus, that torque spec has a safety factor built in. The actual stud torque needed to develop sufficient clamping force to keep the head sealed to the cylinders is less, I'll take a SWAG around 18ft-lbs or even less. The ARP spec is more than twice that.

Higher clamping force (and thus higher torque on the studs) may be required if you can push the peak cylinder pressure higher than the Porsche design, for example if you increase the boost, or use nitrous shots, or alternate fuels. If you build nitromethane-eating engines for drag racing, do whatever you have to do to hold the engine together for that last pass!

For the aforementioned reasons, I would stick to Porsche's specs or only increase them moderately. When I built my engine, I used the Porsche steel studs to replace the lower row of Dilavar studs on my SC engine case, and I stayed with the original torque specs. I didn't see any need to spend hundred$$ more on ARP studs.

Late Edit: And here's another reason not to increase the torque on the studs: The more stress the studs bear, the more susceptible they become to "stress corrosion cracking." This occurs when corrosion attacks the surface of the stud, and with stress on the fastener, the corrosion pitting causes stress concentration, which accelerates the development of cracks. BTW, high strength alloys also generally are more susceptible to this problem. The torsion bars in the suspension are coated in that thick red paint AND coated in thick grease for the same reason, and why the manuals tell you to inspect for any scratches in that paint and to touch it up. I also spray my studs with black epoxy paint before I install them. Belt and suspenders...

Yes, my uneducated guess goes like this. Porsche can do it with 23 ftlb. But we are selling aftermarket 'performance' products. Therefore the customers do not expect or accept failure. So if I was running that promo, I would be adding an extra safety factor - within the limits I had figured nothing was going to bust.
Not dissing any of them - lucky to have these guys in the market and I have ARP in the engine. Just trying to figure why they came to different conclusions for the same solution.
Alan

Different trade-offs. I don't know what those are for ARP or others, but there are almost always many ways to design a part. Cost is a big driver for OE manufacturers. Not as much a constraint for the "performance" aftermarket.

Pete,

Had not considered the Mg case motors as we use factory steel studs in those top and bottom. All with case savers, as if you rebuild one without them, well....

So good point I had not thought of.

Cheers

I was curious so I looked at the torque specs of other M10 studs used in other locations on 911 that are aluminum. I figured If they are all aluminum with steel studs then that amount of torque should be acceptable for head studs to not pull out threads on initial torque as well. I only looked at Aluminum cases and transmission torque specs.

3.0 head studs are 26ft/lbs
Front engine mount cradle is 29.5 ft/lbs
A couple of transmission studs are 34 ft/lbs

I found some references to GM LS aluminum engines with m10 studs having torque specs of 37Ft/LBS



Now some of these are going to be subjected to less additional tension from engine expansion than head studs but gives some comparable information. So 38ft.lbs is probably not going to pull out the aluminum threads unless already damaged. Not sure what it will do to head and cylinder deformation.

john

The stock studs for the 964/993 with the 11 ft # plus 90 deg ends up around 40 - 42 ft #, I would not put that much on a mag case.