ARP Head Studs VS A-1 Technologies Head Studs

[empire0007]

Group, i am rebuilding my motor and currently have ARP Head Studs, but a good friend indicated that the A-1 Technologies head studs are much better.

Anyone has any experience with the A-1 or know anything about them?

[MBruns]

A 1 Tech studs are very good, they are what I use on the 996/997 tt engines, I have used ARP's on many N/A 911's with sucess, but for the GT2/GT3 the A 1's are my choice.

Mike Bruns JBRacing.com

[AlfonsoR]

how much for the A1 studs, what motor will you be using these on?

[chris_seven]

Originally Posted by empire0007

currently have ARP Head Studs, but a good friend indicated that the A-1 Technologies head studs are much better.

What is the reason for his statement? Is a stud just a stud and why do we need to spend so much money or is this another example of skillfull marketing?


Criteria for Stud Choices

Physical characteristics

Dimensional accuracy of threads as this will affect the running torque needed to turn the nuts and hence the preload

Pitch Accuracy as this will affect the accuracy of preload setting and the way on which the fastener is tightened.

Type of thread – machined or rolled. I would always prefer a rolled thread.

Material Characteristics

Corrosion – needs good basic corrosion resistance particularly for lower studs.

There are some specific corrosion issues that need to be considered.

Susceptibility to stress corrosion cracking (SCC) is one area of concern.

Precipitation Hardened Austenitic Stainless Steels – A286 – for example can be prone to this problem particularly in the presence of Chlorides unless great care is taken during heat treatment. I believe Dilavar is an alloy of this type.

Inconel 718 when used in a high strength form can also suffer from this problem.

Precipitation Hardening Martensitic Stainless Steels such as 17-4PH provide excellent corrosion resistance and are less prone to SCC than the above alloys.

Normal High Strength steels such as 8740 can be phosphate to improve corrosion resistance and are not particularly prone to SCC.

Hydrogen Embrittlement (HE) is also blamed for the failure of Dilivar studs but I think this is unlikely. Austenitic Stainless Steels are not particularly prone to failures of this type and the environment in which head studs are used is not particularly hydrogen rich.

It is possible that the studs may have cracked during an earlier production stage of the manufacturing process and not been correctly inspected. I think the latest 993 coated studs are unlikely to suffer from this problem.

Dimensional stability – some alloys can be dimensionally unstable when subjected to long term stress at elevated temperatures and any increase in length would cause loss of preload.
The type of alloys used for head studs would not be affected by the mechanisms that cause dimensional instability so this issue can be discounted.

Modulus of Elasticity – Virtually all of the alloys used for studs have a similar Modulus. Approximately 200GPa. Some Austenitic Stainless steels may be 198GPa and cobalt Alloys may be 210GPa. Not really significant. All of these alloys exhibit a reduction in modulus with temperature – typically a 10% reduction for a temperature increase of 100degC. This change would be linear until at least 250degC. Titanium is different with its modulus being approximately 110GPa.

Coefficient of Expansion – The increase in clamping force and the likelyhood of pulling out studs has been a concern with Magnesium Cases but seems not to be an issue with Aluminium cases.

For the sake of comparison Coefficient of Thermal Expansion is as follows:

High Strength Steel 13.0 ppm/degC

Martensitic Stainless Steel (17-4PH) 11 ppm/degC

Austenitic Stainless Steel (A286) 16.5 ppm/degC

Inconel 718 12.8 ppm/degC

Dilavar 18.0 ppm/degC

The lower the number the greater the preload increase with temperature.

Tensile Strength the absolute strength of the fastener needed will depend on the peak cylinder pressure of the engine being considered. Serious Turbo engines will need stronger studs than normally aspirated.

I have come to the conclusion that providing the studs are dimensionally well made and have rolled threads there is little to choose. Price must therefore be an issue.

I have recently had some standard Porsche steel studs and I must say that they were poor in terms of cleanliness and finish – I won’t buy any more.

It is also disappointing that the washers used for head studs are now NLA for both the early 19mm OD and later 24mm OD sizes.

I have just had a batch of both sizes made in a hardened and ground steel.

I have also discovered that it is cost effective to make studs if you can buy five engine sets.

[empire0007]

Mike wrote:
I have not priced it, it will be going on a 930 3.6 TT built.

Originally Posted by AlfonsoR

how much for the A1 studs, what motor will you be using these on?

[MBruns]

Another good choice is the Super Tec stud kit that Henry designed and sells, I have used several sets on N/A and boosted 911,s.
Mike Bruns

[Turbo_pro]

Originally Posted by MBruns

Another good choice is the Super Tec stud kit that Henry designed and sells, I have used several sets on N/A and boosted 911,s.
Mike Bruns

+1 on the Supertec studs. I have them in 5 of my engines including one high output Turbo and they perform flawlessly over years of use.

[Walt Fricke]

A nice feature of the Supertec studs is that

1) the head end threads are of a finer pitch. This allows a more accurate torquing. Porsche realized this when they changed the thread pitch of the case throughbolts to a finer pitch somewhere about the time of the SC motors.

2) You get complete hardware, including the 12 point reduced head nuts (flange nuts). These nuts, being thinner, are less restrictive to air flow. And if you are twin plugging a race motor, they give more room around that second plug - this is always an issue. Much better in every respect I can think of than the barrel nuts they replace. Of course you can just buy reduced diameter nuts for the stock coarser threaded stock or equivalent studs.

Of course, most of us don't have Chris' background for evaluating thread quality and the like. But I've yet to hear a bad word about Henry's studs.

[empire0007]

i will be looking more toward the A-1

[Turbo_pro]

Originally Posted by empire0007

i will be looking more toward the A-1

Why?

[chris_seven]

I believe that A1 studs are generally made from an AISI H11 Hot Work Tool Steel.

The Thermal Coefficient of Expansion is about 11.9 ppm/degC.

This material is a 5% chrome steel and is generally used for forging dies and other such applications.

I believe Carillo use this material for their standard Con Rod bolts.

It isn't a natural choice for a fastener but its properties are good and I am sure it works well but it is costly.

I have to say apart from the corrosion issues associated with early Dilavar Studs I just don't think the type of material being used is particulalry relevant as at the preload used all the material being selected will have more that adequate strength to do the job.

The quailty of the threads in terms of pitch accuracy, surface finish and the straightness is far more relevant.

The same can be said for the nuts and the washers as it is important that everything pulls up square.

The stud is, however, quite long and will accomodate a reasoanable misalignment without causing too much of an issue.

I have been trying to say, for some time, that in general I think all the aftermarket studs available are perfectly adequate and would let price be a significant part of my decision.

Good, better, best is a bit moot in this type of discussion as the engineering is fairly well established.

IMHO I think Henry's Studs are very good value and clearly have a great reputation. If A1 studs are more expensive why bother?

[empire0007]

[AlfonsoR]

So you got your studs yet? Which did you get?

[Ronnie's.930]

Yesterday, empire0007 went around making waving smiliey posts on many of his old threads (as well as other peoples threads that he had posted in) - maybe someone hacked his user account . . .

[empire0007]

Sorry guys, had the computer open, and my friend though it was funny

Originally Posted by Ronnie's.930

Yesterday, empire0007 went around making waving smiliey posts on many of his old threads (as well as other peoples threads that he had posted in) - maybe someone hacked his user account . . .

[empire0007]

I decided to stick with the ARP

Originally Posted by AlfonsoR

So you got your studs yet? Which did you get?

[Walt Fricke]

I have an inheirated set of ARPs on one of my engines, and have noticed one small improvement Henry might consider for his Supertecs:

Bullnosing the top of the stud makes getting the washers and nuts on easier.

I pulled the heads up as a bank, leaving all hardware in place after turning the nuts off their stud threads. Then I reinstalled everything. All I had to do was stick the socket down the hole and turn to get the nuts started again. Washers were all in place, and the nuts were sitting over the bullnosing on top of their threads.

Earlier, with the nuts and washers out, all I had to do was drop the washers in, and they fell over the studs. And in most cases, dropping the nut in had the same result. No fussing around with a magnet or screw driver to get things started.

Not super important, I know. But for a race motor, where it is apart often, these small things are very welcome.

[Henry Schmidt]

Originally Posted by Walt Fricke

I have an inheirated set of ARPs on one of my engines, and have noticed one small improvement Henry might consider for his Supertecs:

Bullnosing the top of the stud makes getting the washers and nuts on easier.

I pulled the heads up as a bank, leaving all hardware in place after turning the nuts off their stud threads. Then I reinstalled everything. All I had to do was stick the socket down the hole and turn to get the nuts started again. Washers were all in place, and the nuts were sitting over the bullnosing on top of their threads.

Earlier, with the nuts and washers out, all I had to do was drop the washers in, and they fell over the studs. And in most cases, dropping the nut in had the same result. No fussing around with a magnet or screw driver to get things started.

Not super important, I know. But for a race motor, where it is apart often, these small things are very welcome.

We cure that problem with a simple magnetic socket.
You can buy one or make your own by simply gluing a small magnet in the bottom of a twelve point, 1/4 drive socket.

[Henry Schmidt]

Originally Posted by chris_seven

It is also disappointing that the washers used for head studs are now NLA for both the early 19mm OD and later 24mm OD sizes.

For any of you that need used studs, washers (large and small) and / or nuts, we have hundreds.
Cleaned, gold zinc plated and baked to prevent nitrogen embrittlement.
Discounts for qualtiy and or sets.

[chris_seven]

We made ours in 17-4PH with an H925 Temper