toddk911

Possibly. All I know is that he did not seem to be concerned with the specific tq amounts.

Been about 4-6 months running up to 18psi and no leaks or coolant smell.

gt37vgt

snake oil if i would go to the trouble of getting the old ones out i'd upsize to m14 . so do you realy see any improvement in relyabilty with those studs . here all kinds of yarns blaming the factory studs for head gasket failure any true stud failure ?? any one measure an old set of factory ones . any one seen good back to back conparison

333pg333

From what I understand the factory ones are pretty big in comparison to many out there. Check out a 911 if you have the chance. I understand it's not the size, but the old threads that can be responsible for stretching?

KuHL 951

I think the interest for many people is when they've pulled a head two or three times after HG failures/leakage they want the added insurance. At higher boost levels like many run here it's worth it to know that the OE studs haven't been cycled and torqued countless times. It's not a myth that any bolt stretched over and over will relax and become more ductile if over torqued. What is a failure to you? A clean ductile break or stretching under severe conditions of boost and compression ratio? The ARP and RaceWear studs do not do this; their design and material choice starts off with the premise that any torque under 100 ft-lb will not cause the stud to yield. If you feel they are snake oil that's fine; unfortunately most respected builders of performance engine would disagree with you on that. (and no I'm not one of those builders). Check the vids of ST's dyno run and watch the head lift at the end...it might have been 'snake oil' coming out of that head at 24psi but it looked like coolant to me.

Are they overkill for most purposes? Probably. Are they better than a 20 YO head stud? Yes

evil 944t

I think your assuming a lot here. Its possible he had other things going on like a warped head. Maybe he will chime in here. Ask him what he is using now..

I agree that ARP and Raceware studs are better than a 20yr old stud but so is a new factory stud. Once you change the stud and everyones uses their ubber tighten methods, you compromise the threads. Sure the new studs torqued to 1000psi won't stretch but what do you think is happening to the threads??

The only reason I would go to larger studs is to cut new threads in the block. Then design a stud that does the stretching rather than have the strength in the threads.

I have custom 14mm studs that I will be using in my 1000rwhp motor but thats again to "refresh" the 20 yr old blocks threads.

toddk911

Are they cheaper than new stock studs? Yea

I would gather there are more people running a lot higher boost with ARP/Raceware studs on all makes of cars than being run on 951. There are maybe 10 951 total running over 25psi and maybe 20-30 running over 30psi?

In FL alone there are probably 500 people/cars running over 30psi on street cars, much less track cars. And they all seem to be running ARP or Raceware studs.

Oddjob

You guys familiar with Young's modulus/Modulus of Elasticity, stress strain curves, elastic and plastic deformation - good old metallurgy/materials science?

The only reason that ARP or Raceware studs would stretch less than a factory stud is if they have a larger diameter. I believe they are the same diameter, correct? Any steel, regardless of alloy, high or low carbon content typically has a modulus of elasticity around 28-29x10^6 psi. So it really doesnt matter what brand/alloy the studs are, they will stretch the same amount/distance if the same torque/tensile load is applied.

All studs and torque specs will be designed to be within the elastic deformation region of the stress/strain curves. Yes, if you exceed the tensile strength of the stud, it will permanently stretch/deform (plastic deformation). And, its likely that the ARP/Raceware studs may have a higher yield/tensile strength than the factory studs (but does anyone know for sure what these specs are for the various studs?), but it wont matter in the torque ranges that we are dealing with.

Anyone snapped a factory stud? If so, what were you doing to it? Anyone permanently stretched one, so its permanently longer than the others? Or, if overtightened, will the first mode of failure be the alluminum threads ripping out of the block?

I suppose its possible to have a fatigue failure from excessive use, but I cant imagine how many times you would have to have the head off in order to cause a fatigue failure with a head stud.

evil 944t

Jim,

I have had the threads give out with stock studs and stock torque procedure. I also use thread reforming taps rather than cutting taps.

I agree, the only way to build a stud that will stretch is if you waste some of the diameter(tappered design). That way it will stretch in the wasted part and not pull on the threads.

Oddjob

The threads on the stud, or the threads in the block - I would expect the block threads, correct?

evil 944t

Yes, sorry about that, The threads in the block.

gt37vgt

well the non cutting tap is a great idea for the soft aluminum you can even just grind flats on an old stud for similar effect seems to me that the alloy thread is the weak link and gets weaker when you mess with it to change to a similar stud i will carfully examine my studs for streatch then proceed . while were on the subjuct were do i get good rod bolts?

special tool

Dave is right.
In the end I went with stock studs and Cometic.
I have fixed the headlift problem which had nothing to do with the head/block interface on the 944 - that is fine.
I have already run over 30 psi with a MUCH bigger turbo, and there is ZERO lift/detonation.

Because of my experience, I advise (to whoever asks me) Porsche studs and Cometic stainless 3 layer.

evil 944t

Who's asking? Dude, Derek and I will be in Ct. on thursday, you around?

ps - Derek's mailbox makes more hp than your car on 30+psi

billthe3

Were these new studs or ones you were reusing? Also, what did you torque them to?

special tool

Yeah!! - call when you are here.
But leave the derelect at the bottom of my driveway.