ARP vs Stock studs
 

Guys,

Currently going through a full top and bottom end rebuild. Trying to figure out whether to buy OEM studs (head studs, connecting rod studs) or, whether to spend a tad bit more and get ARP.

For the head studs - what are my choices. I hear a lot of Dilawar studs and the controversy that surrounds all of the OEM studs. I am looking at these ARP head studs: http://www.amazon.com/ARP-204-4206-Head-Porsche-911-930/dp/B0057Y7A48

For the connecting rod bolts - what are my choices? I am looking at these ARP units: http://www.amazon.com/ARP-204-6003-Connecting-Rod-Bolt/dp/B00IKAEWFG

Also - I came across this engine case kit from ARP. Would this be a good investment or, is factory stuff more than sufficient? https://hinsonsupercars.com/p-20216-arp-504-9501-porsche-911-930-turbo-case-stud-kit.aspx

Not doing anything crazy with the build --- 79 SC 3.0 with CIS and going to 964 cams and higher compression pistons 9:5.1

Look forward to hearing!

Regards,
Paul

This question keeps going around and around.

Standard steel studs on a standard Alusil engine case should be just fine.

Rod bolts don't seem to fail but use new nuts.

If you use ARP Rod Bolts you will have to re-size the big ends as well.

I got ARP head studs - and then some engine builders on this forum tell me they won't use them.
Rod bolts yes, but studs no. Supposedly come loose (at the heads) - but I can't verify that.
Alan

I don't know why so many think that ARP is the Golden Fleece for rebuilds. At least one person has the heads come loose and posted here. If you're going to upgrade the head studs, look at the supertec units with the fine threads on the outside for better adjustment of torque much like the factory uses on the through bolts from 3.0 on. The last several mag cases I built I used the the fine thread through bolts for better hold and torque adjustment. The factory items are sufficient for street building.
Bruce

One of the main issues with aftermarket studs and magnesium engine cases with aluminium cylinders is concerned with the core diameter (shank) of the stud.

If the core diameter increases then the additional force created due to expansion can be a real problem.

The force generated by expansion can accurately be described as irresistible and for a given Young's Modulus (E) is proportional to the square of the diameter.

If you increase the basic stud diameter from the 7.6mm of the standard stud to around 9.5mm then the pull our force generated will be 1.6 times that of the standard stud - something I would try to avoid on a magnesium case.

I can't see why an ARP stud should come loose at the head unless they are fitted without thread locker.

I realise that ARP suggest installation without the thread locker OR that the studs should be torqued before the thread locker sets which would be a real pain without special tooling.

Bottoming a standard stud into the hole in the case is not wise as this will cause issues with uneven loading due to the poor quality thread at the end of the blind hole.

The optimum solution is to use a stud with a 'dog' point that can bottom into the hole avoiding the poor threads and allow the stud to be torqued to about 12 lbsft before the threadlocker cures.

We have been making Titanium Studs with this design, specifically for Magnesium engines for about a year.

The Ti also has a lower modulus so that the increase in 'pull out force' due to expansion also reduces.

We use a fine pitch at the head end but this is so we can use a 928 - 12 point con rod nut which has a much lower cost than an ARP 12 point nut. We also make 17-4PH stainless steel ground washers.

The end of the stud is broached to allow them to be installed with an Allen Key.

http://i197.photobucket.com/albums/a...pspczsg1gx.jpg

We have them in around 10 engines so far and they seem to work well.

Memories. ..

I have the arp but lust after a set of Chris's titanium. Next rebuild perhaps...

Chris - I am about to build my bottom end with ARP rod bolts. I was unaware that any "re-sizing" needed to be done - exactly what are you referring to here?

Need for resizing the big end......
 

I've done a few SC engine rebuilds using ARP rod bolts and not been aware of this process (?). Could someone elaborate on this subject. Thanks.

Tony

Tony - as far as I know the 'issue' is with the head studs. There is a discussion - I think in the 930 forum recently (last 3-4 weeks) on this issue. The rod bolts apparently are rock solid.
Regards
Alan

It's always a good idea to get the rods rebuilt whether using OEM bolts or ARP. The shop shaves a little off the cap mating surfaces, installs the caps using the ARP bolts or the original bolts if using OEMs then hones the big end to spec. Then they install new bushings and hone the small end to set both the center to center distance and pin/bushing clearance. If you're reusing the pistons/pins they'll want your original pins to size the bushing or a new pin.

Paul

I think the ARP rod bolts you need for a SC are 204-6005 and not the 6003 version you posted.

We have sold over 1200 sets of Supertec head stud kits to over the last 12 years and to date have had ZERO complaints.
It is the number one selling head stud kit on the Pelican Parts website.
They are used by professional engine builders and DIY enthusiasts for both street and racing application.
They are selling so well that we are struggling to keep up with demand.
I notice the Chris has copied some of our unique design features to make his titanium studs which is indeed quite flattering.


Supertec Head Stud Kit

http://forums.pelicanparts.com/uploa...1457160707.jpg

Henry,

I don't think you can call using a different thread pitch in order to use a much lower cost 12 point nut copying. :D

If the 928 con rod nut had been a standard Metric Coarse we would have used this thread pitch.

The best price I can buy genuine ARP 12 Point nuts in the UK is $6.00 each and I pay $2.00 for the 928 Con rod nut which is nearly 100 bucks difference for an engine :eek: and worth saving.

Which other features do you believe we have copied?

The material we have selected is different.

The shank diameter is different

We have added a 'dog point' and broached the end to allow installation with an Allen Key.

I would accept that the case thread is also the same but this is not really an option.:)

I had no intention of copying your design and as we only use these studs 'in house' I would hope it doesn't become an issue but we will consider using a different nut in the future. May be a prevailing torque silver plated K nut would work. :) I will buy a batch and check them for variation in running torque.

I hope that doing this won't offend Casper Labs who also use a prevailing torque nut.

The use of a fine pitch in stead of a coarse pitch is interesting as an exercise but I am not sure that the torque/preload levels used in 911 head studs it has much practical significance.

It is true that a finer pitch will have a greater mechanical advantage than a coarser pitch and that for a given torque the preload will be greater but the increased friction created by the longer thread length will tend to reduce this effect.

In practice if would look at the increase in axial load created by the geometric difference and then factor in the increase in friction the difference in 'one pitch' size is less than 5%.

If we then consider that preload using simple torque control, even in a perfect world, is likely to vary by 25% then the differences can simply be neglected.

It is fair to say that the stress in the nut will be lower with a fine pitch but at the torque levels being used I think this is irrelevant.

It is also fair to say that the fine pitch is also more resistant to shaking loose but again I am not sure if this is a major issue.

The subject of ARP nuts coming loose is interesting and worth some consideration.

In general it would b difficult to determine if the nut has simply shaken loose or if the stud had come loose from the case if ARP's recommendation had been followed and the studs had been installed without thread locker.

ARP also suggest a higher torque figure and if this is used in a Magnesium case the extra preload could cause stress relaxation to occur in the case and this would reduce preload and allow the nut to loosen.

With regard to con rod bolts ARP recommend that rods are re-sized after new bolts are installed as it is possible that the increased preload in the bolt may cause the big end to deform slightly and this could cause a bearing to pick up and will affect crush heights.

Just swapping fasteners is not always a great idea.

We are also in the process of designing a replacement Case Bolt set. We are planning to use a Tie Rod which will also prevent 'shuffle' by effectively pinning the engine cases.

Watch for oem fracture split rods though as this technique would ruin them.

Good morning Chris
There is no issue at all. Like I said, "it's flattering".
There are many companies attempting to make a replacement for 911 head studs and competition breeds innovation...If you design a better head stud that is also cost effective, I may even use them. After you have two or three hundred sets in hundreds of engines with 100,000+ miles of success, let's revisit the question.

I appreciate these head stud discussions on forums throughout the internet because EVERY time they occur, our market share increases. Head studs are almost meaningless to our bottom line but my ego appreciates the validation.
Cheers

I have to say, I don't see anything I'd call copying taking place. There are loads of other Porsche products which clearly get copied but these parts seem quite different to me, or at least as different as fasteners for a specific application can be.

Has anyone thought about making cylinders like an aircraft engine where they bolt to the case and then the heads bolt to the cylinders?

"Has anyone thought about making cylinders like an aircraft engine where they bolt to the case and then the heads bolt to the cylinders? "

Make the cyl. and head all one piece like the old P&W radials. Just have a bottomless check book.

Well, Porsche did weld the heads on to some of their turbo motors- 962 I think and Moby Dick. I figured that if LN Engineering can manufacture the Nickies they might be able to do something like a Lycoming cylinder.

Chris, in your opinion, how about steel studs on a 930-10 204 hp Euro with Nikasil?

We use standard steel studs on Aluminium SC cases all the time and have done for 7-8 years and never had a problem.

The 'class' of thread on a Porsche supplied stud seems better than any of the aftermarket studs when checked with typical 6H go/no-go gauges so the 'rock' a little less when fitted.

This is the main reason we only use our Ti Studs with Magnesium cases which are more prone to
suffer fro stress relaxation and pull out the thread.

I worry about Dilavar because Precipitation hardening Austenitic Stainless Steels to tend from intergranular corrosion in the presence of chlorides and I am not sure how long the coating on the latest 993 studs will last.

I have bought things from Chris and Henry.
Both sell good stuff.
I cannot attest to the quality of the studs Chris sells but I would have no problem buying them if I was not already using Henry's Supertec headstuds. Like he said, zero issues, zero complaints!

Max,

EB Welding the heads to the cylinder isn't too difficult and will eliminate cylinder head joint issues.

I don't think it will help with pulling studs out.

I was thinking of the aircraft style cylinders, not welding the heads. The stud gets shorter but the thickness of the clamped aluminum reduces by the same amount. I guess that would cancel out?

Yeah Damn It... I have to keep a set in stock cause he is always selling out. But to his credit, Henry has always made sure I was never held up on a build. Good product and great attention to detail. I sure do like the idea of an allen key to install the studs. Maybe even a depth notch to know you've gotten them to a sufficient thread depth without using a measuring device? What do you say Henry? Maybe a serration or something to ensure proper penetration. Kinda like ribbed for her pleasure. :eek:

:eek:

Now this is my kinda' thread!!!

:D

Based on your hype, Henry, I figured you had sold a million sets by now.

If by "hype" you mean pride, you are entirely correct.
I am proud that so many builders in the Porsche community have the confidence to choose our product to enhance their labor of love.
Porsches are more than a car, they have character as do the owners and if they found fault in our product, they would shout it from the roof tops.
To those who have made our product such a success (all be it only 1200 sets), I say "thank you".

1200 looks like a solid number to build a reputation on. Statistically robust a statistician would say.
Well done Henry.
Alan

Interesting comment but I don't think it is correct.

I am not trying to make a comment about the quality of a specific product just how we should make an assessment from a design perspective.

Whilst 28800 studs is a good number statistically there is no published data so no real conclusions can be made other than as Henry states he has received no complaints but it would be impossible to sell critical fasteners for many applications on this basis but we can draw some conclusions.

The first point to make is that the standard steel stud used by Porsche rarely suffers failure. (Clearly discounting Dilavar)

If we took a rough guess at the number of steel studs produced during this time then I don't believe that 5 Million parts would be excessive so we can be confident that the 'base' design is sound.

As there is no real test data showing a traditional Weibull Distribution/operating conditions or test results then all we can draw from this observation is that the basic stud has an extremely low stress ratio and that it operates well within its fatigue crack initiation threshold. It is clearly 'fit for purpose'

It shouldn't, therefore, be difficult to make a suitable replacement.

If we then 'design' and manufacture a stud using a different material and some other detailed changes we need to consider the impact on the life of the part.

If we chose a material with either enhanced mechanical properties in terms of yield strength, tensile strength, ductility and possibly fracture toughness then we can be fairly confident that failures won't occur.

If we also increase the cross-sectional area we reduce the stress due to preload but increase the stress due to expansion so they tend to balance out depending on the precise duty.

The load on the threads increases but the stud is relatively unaffected.

Once we have looked at basic stresses it is also important to consider the operating environment and ensure that corrosion and other issues don't dominate the behaviour of the part. - Something Porsche clearly didn't manage well enough with Dilavar.

If all these aspects of a new design look favourable then as a Metallurgist with a speciality in Engineering Materials Behaviour I would be comfortable to use the part and to recommend it to my colleagues.

I do believe that Henry's Studs clearly fall into this category and have no doubt's about their reliability.

However, having been involved in Probabilistic Failure Design early in my research career, I don't believe that I could offer any statistics to back up this statement and it is at best apocryphal.

The cost of doing the work to make either an Insurer or Safety Agency happy would be eye watering and in the case of a head stud a waste of time unless it were an Aero engine part :)

The real problem with 'our' industry is that a huge number of parts are being sold using baseless claims, many of which are completely untrue and used to hide either a complete lack of engineering knowledge or just a simple lie.

Clearly Henry does a much better job then many of his competitors but in general caveat emptor does apply.

When we design a new or replacement product we always produce a 'Technical Construction File', we carry out a basic stress analysis, we look at the impact of changes of material and the risks associated with failure and we consider all environmental aspects of our choices. We take either a conservative or pessimistic approach and if we are not 100% confident in our choices we don't proceed.

We would always be prepared to explain an justify the conclusions we have reached and why we believe them to be appropriate.

Chris, your point is?
You spend a great deal of time bloviating and we spend our time testing by actually running the product in it's intended application.
The statement "Zero complaints" is a reference to more than just breakage. It applies to failures of any kind reported to us about the product in the environment it operates.
That means no breakage, no pull outs and no reports of loosening nuts, no reports of leakage at the cylinder/head joint.
I appreciate your attempt to critique the products you encounter and your expertise is well documented but really aren't we as engine builders interested in success rather than sudo scientific head scratching?

My point is that there is simply no data and hence 'statistically' there is no correlation that can be made.

To simply state 'we have no problems' is, of course, useful but it does not fully substantiate a design. I do accept this statement as the complete truth but was just trying to point out that an Aero Engine designer would need much more as he would have to show real stress levels, real pull out forces and a great deal of fatigue analysis.

I would be happy to elaborate but I don't really believe that you are interested.

The definition of pseudo is as follows: not genuine; sham

If you are making this as a point then you are being quite insulting as the comments that I endeavour to make are based on a lifetime's work studying Engineering Materials Behaviour and are to the best of my ability and knowledge fairly accurate although I do accept that I don't always provide all of the math.

Suffice to say that I am sure that the studs you sell are more than adequate for the job they do, which is a comment, I believe that I have made many times.

This brings me to a the second point I was trying to make which is that without data it is impossible to support a real argument hence my comment on another thread about a 'religious' belief.

Without real data we either believe or don't believe, we can make subjective judgements which we can either accept or dispute but there is nothing we can show to prove a point.

Karl Popper makes this point far more elegantly in his book 'Objective Knowledge'.

For years now you have described my comments as 'theory' and not based on practical experience but in fact you have little or no idea of my working life and the projects I have been involved with in the last 40+ years.

I find it amusing that you take this view and do accept that the argument between Science and Practice has been going on for a few hundred years and sadly it seems to me that 'practical engineers' find it hard to accept that both approaches are needed to provide complete solutions and a real understanding.

Whilst I don't agree with all of your comments I hope that I don't make any insulting remarks and I hope you realise that disagreeing with someone's opinion is not an insult.

I could just accept that it is impossible to make any comment about head studs on this forum without offending you but where's the fun in that :)

Chris
I guess my point is we can talk a load of crap and continue to use products we know to fail or we can get out and try to improve the process.
Progress belongs to those willing to try something new, observe the results and offer sound, honest opinions based on those observations.
Do I have a scientific understanding of metallurgy or engineering principles? No
What I do have is a love for the process of rebuilding and improving the air-cooled Porsche engine.
Would I lie about my observations to sell some hardware? Hell no
When you suggest that observations based on years of experience have no validity you insult the person offering those observation.
If discounting my experience is your intent, where's the fun in that?

Henry,

I have spent the majority of my working like in a Research environment and have had a significant input into the design and development of test systems that measure and provide the data required to be able to make progress for many years.

My point was to suggest that without data we must either believe or disbelieve and I am surprised that you are trying to twist my meaning to suggest that I am trying to say that you are not being truthful or that the observations you make are not worthwhile. I am merely saying that in my view real data would be useful and I believe that in general the Engineering community would agree.

Without data and design any product development surely becomes 'poke and hope'.

This approach really does slow down the pace of engineering development because of the timescales involved in obtaining a result.

I found your comment in regards to the Ti Head studs we manufacture to be interesting.

Your comments were roughly as follows:

'When you have 2-300 hundreds of sets in hundreds of engines with 100 000+ miles of success we will re-visit the question'

I assume that this means that Supertec didn't sell any studs until you met the same criteria or did your experience of engine building help you to produce a stud that my Engineering and Metallurgical knowledge couldn't emulate?

To carry out such extensive testing is clearly unaffordable and we need some way of shortening this process.

Where we should agree is to accept that by using 'prior art' and 'experience' we are starting down the path of good practice which is completed when we produce good data to back up our observations with scientific explanation which enables us make much better decisions.

I co-edited a book in 1996 entitled 'Computational Methods and Testing for Engineering Integrity' which sheds some light on the methods that I believe we should try to use whenever possible.

I am happy to accept your studs do a great job but as you know I question some aspects of their design in terms of Magnesium cases, hence the stud we produce.

I have never questioned your experience but this does not mean I believe that you are infallible.

We don't have to agree in all areas and it is unlikely any of us has a 'perfect' solution.

As you well know the 'fun' in debating the best solution is to have our ideas and propositions challenged and questioned. It makes us focus on our assumptions, justify our decisions and think through our efforts in a hopefully constructive manner.

From time to time it also helps to make us aware of our mistakes.

We have a small team of only 3 people involved in our product development and we constantly question and challenge our decisions and I hope this helps us to make better products. My two colleagues are both Mechanical Engineers and I tend to focus on materials.

If you feel, however, that a scientific and engineering explanation of a product is crap then we are really wasting our time in debating this subject.

You are correct. When we started making head studs we did not use them in customer engines. We spent 3+ years testing them under racing condition before ever selling a set. In the early stages we tried four different designs in an attempt to get it "right. I never wanted to be in the stud business, I just wanted a better stud for the engines I built. All told we went through seven different iterations before landing on the present configuration.

I enjoy the discussion as well it just seems that some of the discussion questions my integrity and I will not take that lightly. I may be overly sensitive (rarely accused of that) and if that is the case I apologize.
I consider you a friend so challenging your comments is not done lightly either.
I welcome your comments but I lack the patience for condescension

In other news, Stuttgart translates as "stud farm." (Old German)

Pass me the pop corn..

I've used steel, one set of ARP and 2 sets of Supertec.

Steel was fine for stock.

IIRC the ARP had a coarse thread on the head end and all the treads felt rough. The rounded end of the stud seemed nice at the time. The rough threads were a surprize to me as comparatively the ARP rod bolt threads were fine.

Henry's studs were super nice quality, smooth as silk treads and nice thick washers. No problem putting nuts on (negating the ARP rounded end) and perfect for using a full size 14mm twin plug.

No real issues except some head weep on the ARP, but it is on a high boost 930.
Also a bit of weep on steel, high milage stock engine built late 90's.
Not enough time on 2sets of Supertec to report.

YMMV SmileWavy

Ever get stuck on an elevator ride with someone who farts loudly? It's not enough to just have heard it once. No, no way. Then you smell it...inescapable agony. If they lack decorum they next describe to their captives what they had for dinner the night before to produce such a noxious cloud. Not taco night for sure... maybe broccoli or brussel sprouts you guess to yourself. This is every headstud conversation on Pelican. Whoever smelt it dealt it, whoever denied it supplied it... but we all heard and know the first offending tooter polluter. Please toot your horn once per thread/elevator ride if you must... please also refrain from wafting it about.

That's odd... my ARP head studs were smooth as butter, and could have just about passed for jewelry.
I put mine in to the case with red loctite, but so I'm curious to see if the nuts loosen at some point like some people have reported.

Other ARP studs were likely counterfeit. Becoming more and more common in today's world.