Raceware studs for 911E engine

[hipdoc]

I am considering putting a set of Raceway studs on my 73' 911E since I am using JE 11:1 compression pistons with twin plugs and electronic ignition. Does any one think I would have to have the case modified, i.e., time certs placed since I am changing the pistons and studs? I hear Ollie's does this type of modification. Let me know what you think.
Thanks,
Doc

[Steve@Rennsport]

If your engine case doesn't have Case Savers, this is the time to do this, especially with that CR.

I would not use Raceware or ARP studs; we use 993TT Dilavar ones, ONLY.

[boyt911sc]

Originally Posted by Steve@Rennsport

If your engine case doesn't have Case Savers, this is the time to do this, especially with that CR.

I would not use Raceware or ARP studs; we use 993TT Dilavar ones, ONLY.

Steve,

Could you help us understand why the 993TT Dilavar studs is a better choice for this particular engine rebuild? Would this recommendation be still applicable for 3.0 SC and 3.2 Carrera motors? You have the knowledge and experiences in engine rebuilding that we could only dream about. Thanks.

Tony

[Steve@Rennsport]

Hi Tony,

Dilavar matches the expansion rate of the cylinders better than anything else and this keeps the heads sealed.

While Raceware & ARP studs are both quite strong, I've found far too many loose heads to use them anymore. Their expansion rates are pretty far off for an aluminum cylinder, but they may work for a Biral or iron one.

We've been using the 993TT Dilavars since 1995 without a failure and while expensive, I feel its the best choice.

[Tippy]

I reused the 993TT studs on my boosted 3.4 (3.2 base), without issue for over 5 years per Steve's advice.

I'm running 21 pounds of boost and flog it every time I drive it. Should be around 650hp (haven't backed up claims, rather a well respected tuner said what my combo should bring), so it gets a little workout.

[Henry Schmidt]

When you're building a high performance mag case engine you should always use CaseSavers not Timeserts.
11:1 compression will create a lot of heat and high cylinder pressures so it is incredibly important to add the largest oil cooler you can.
Although many "experts" use 993TT studs, we haven't used them for years.
That means hundreds of engine built using Supertec head stud without a single failure.
We have also sold nearly 2000 sets of our head studs without a single reported failure.
Although 993TT head studs are less likely to fail than previous versions of Dilivar studs, we have seen and documented in this forum failures associated with their use.
Many profession engine builders as well as hundreds of amateur builders have found that Supertec head studs offer a more stable platform for cylinder to head sealing.
This proprietary design facilitates twin plug connector clearance, zero failures and ease of assembly along with the aforementioned stability.

[Mark Henry]

I went with Supertec studs on my build and a couple 930 builds, no leaks or issues.

I have a buddy with a 930 that sounds a lot like Tippy's, he used ARP and he's always complaining that his cylinders are weeping.
That said I have ARP on my Nickies type 4 engine in my '67 bug without an issue, but it's a 9.2CR N/A 180hp engine.

[chris_seven]

I have to agree with Steve with regard to magnesium cases and I would support his comments about using Dilavar on this type of engine, but I still like Timeserts.

The basic design and material properties support this comment.

The increased pull out force caused by the expansion of the aluminium cylinder is quite significant when you consider a steel stud and I made some detailed calculations several years ago.

It is worth repeating the basic mechanical loading that is present so we can understand what is going on.

I have posted these numbers a few times and they are reasonably accurate as the mathematical model of cylinder expansion is quite straightforward.

A head stud with an M10 thread will generate a preload of around 5000lbs at the torque figure used on a typical early 911 engine.

This preload will be identical for a given torque regardless of the stud being used. There will be some scatter due to thread friction and general repeatability but this is a good average value.

As the cylinder expands there are several factors that need to be considered.

The first and most obvious is the difference in coefficient of expansion of the studs compared to the cylinders.

All Ferritic steels have virtually identical coefficient of thermal expansion (CoE) which is around

11 x 10^-6 mm/mm/degK.

Aluminium is about 20 x 10^-6mm/mm/degK as a comparison.

Dilavar which is Austenitic is about 18 x^-6mm/mm/degK.

It should be clear that the greater the difference in CoE the greater the increase in preload and hence pull out force.

The next influence is the Modulus of Elasticity (E) of the stud.

The lower the E value the lower the increase in the preload due to expansion.

All steels, either Ferritic or Austenitic, have E values which will only vary by 2-3% and we can neglect these differences as being insignificant.

The last feature that is important is the basic design of the stud.

The larger the diameter of the 'shank' of the stud the greater the increase in preload due to expansion.

A standard steel stud has a shank diameter of 7.6mm and this results in an increase in pull out force of around 1400lbs for a temperature increase of 100degC.

A factory Dilavar stud will limit this increase to around 200lbs and will give the case a much easier time.

This is due to the fact that the shank diameter is virtually identical to the original steel stud and the material has a CoE close to Aluminium.

If we now increase the shank diameter of our chosen stud from 7.6mm to say 9.5mm we will see an increase in pull out force that is directly proportional to the square of the diameter of the shank.

This means the pull out force will increase from 1400lbs to around 2200lbs.

If the thread in the case will support this increase all will be well but if it is an old Mag case which is suffering from stress relaxation and has lost some strength this increase could be an issue.

The real issue is not to consider the stud in isolation but to consider the entire structure that you are trying to bolt together and all relevant aspects of the design.

We use a Titanium Stud with magnesium cases as we make them at a lower cost than Dilavar and the reduced modulus limits the increase in pull out force to around 600lbs and they are working well.

For aluminium cases we just use standard steel studs as they are cost effective and seem to work well.

I could happily accept that 964 and 993 engines could benefit from studs which can be tightened to a higher torque.

[theiceman]

to sum it up ...
magnesium is the weakest of cases when compared to alluminum.

11:1 CR is way above factory spec even for aluminum for that engine so imagine what it is going to do to mag case.

re-enforce it every way you can , and reduce stresses as much as possible.

[Mark Henry]

VW bug type 1 guys have been going through this long before the 911 guys, case savers is a routine job for the mag cases.

In the later years (1970-), when VW went from 10mm to 8mm head studs, they came right from the factory with case savers.
I always wondered why Porsche didn't follow suit.

[Henry Schmidt]

A few notes:
CaseSavers are the preferred method for mag cases, period.
The Time-Sert external threads are finer and as such offer far less stability under load.
I would estimate the failure rate with Time-Serts is 20 times higher than CaseSavers.



As for head studs:
I am very impressed by all the theoretical engineering but real world application shows that there other considerations as important and perhaps more important than simply expansion rates.
Along with increased cylinder to head stability, the Supertec stud also offers improved assembly possibilities not possible with standard Porsche head stud design.
We have never seen or heard of a Supertec stud failing (under any definition) in a real world application. No one can say that about any other stud.

These statements are my observations and the observations of professional engine builders around the world so my conclusions are based on those observations not theoretical conjecture.

[chris_seven]

Henry,

Sadly the influence of stud stiffness on the preload produced in a fastener that is used in a joint subjected to thermal expansion is neither a theory nor conjecture.

The fact of the matter is that the stiffness of the bolt has a substantial impact on he preload produced.

This is well understood and very well defined in the world of 'real engineering design'.

As the stiffness of the cylinder and the head will be constant the greater the stiffness of the stud the greater the force resulting from a given expansion.

It is simply down to very basic Physics and in terms of preload increase, if we increase the stiffness of the stud then the force generated by expansion will increase.

As the stiffness of a stud is directly proportional to its diameter the greater the diameter the greater the preload increase.

I do realise that you don't want to agree but sadly it is just indisputable.

[Henry Schmidt]

Chris, I'm not arguing with the "basic" science or the engineering, just your conclusions.
My experience is that the increased preload (provided by our stud) is desirable and real world experience would seem to reinforce that conclusion.

We will continue to have this discussion ad nauseam but I have seen the draw backs of the Dilivar stud and the ability to correct those shortcomings with a different stud design.
So we will continue to agree to disagree.

[Mark Henry]

I'm pretty sure the real engineers said it was indisputable that the Titanic was unsinkable.

Henry has stated that he consulted with "real" engineers, when designing his studs, after that he tested several candidates. He picked the one that he felt did the best job.
Engine builders use what they know and have never let them down in the past, some builders swear by curilT, personally I have no use for the stuff because it has failed me more than once.

Until I hear of Supertec stud failures I will continue to recommend them as a replacement of the dilavar studs, which I have seen failures and the ARP, which I have seen weeping and requiring retorquing. I too will use steel on stock engines.
I won't be testing another stud unless someone brings me different studs that they already purchased or the supertec's start snapping like dilavars.

[nimbus]

Chris_seven, I am interested in your Ti studs as a replacement for Dilavar or steel studs. Do you sell these Ti studs? Can you please provide a link to your site?

[chris_seven]

I am sure Henry and I will continue to disagree about the optimum stud to use on a Magnesium engine. I have no concerns about this issue when we consider Aluminium engine cases.

Just consider the basic facts.

Magnesium engines do suffer from studs pulling out of the case.

It is the increase in preload caused by expansion that causes this failure mode.

Stud failure is not really the issue, it is the long term behaviour of delicate and difficult to replace engine cases that we should worry about.

How can an increase in preload be helpful?

Whether or not the Titanic sank is completely irrelevant and the statement commonly quoted was, of course made by the marketing department  Any sensible engineer would know better.

In this case material properties such as linear coefficients of expansion, Modulus of Elasticity and tensile stresses creates a very simple model that involves some very, very basic engineering and that can be easily solved using straightforward arithmetic.

I would point out that elastic tensile stresses should always be considered to be stable, it is compressive stresses that create buckling and instability.

We have just completed a programme of work where we have used a load cell to measure the relationship between torque and preload of a range of different studs and different tightening techniques.

We have a damaged magnesium engine case half and we are in the process of studying the force needed to pull out the thread and the improvement obtained by using a Timesert.

We also plan to apply strain gauges to several studs so we can log the preload generated due to expansion and in a running engine.

We have a datalogger that will write data to an SD card so we can record engine temperature and look at 4 x different studs.

We can calibrate the strain gauged studs using the basic load cell and should be able to measure force to an accuracy of around 1%.

We will carry out this work using a 3.0SC engine which we are building this month.

Once complete we will make the results and our conclusions available.

[nimbus]

Chris, do you sell these Ti studs? If so, how can I purchase them?

Regarding your proposal to instrument the studs on a running engine, all I can say is good luck. We have struggled in the past with similar strain-gauge instrumentation projects to get 1% accuracy in a fully static application and I can imagine that your signal will be substantially corrupted by combustion and inertial loads. May be possible with sufficient low-pass filtering. I would reach for a time constant of tens of seconds.

[Henry Schmidt]

Chris, you continue to make bogus assumptions.
Mag case stud pull out can be controlled by reducing excessive heat (the major cause of stud pull out) and inserting the case to repair damaged threads.
New mag cases (never overheated) rarely experience pull out if the temperature is controlled even without inserts.
We have never seen head stud failure using CaseSavers, Supertec head studs and the appropriate temperature control.
Your argument seems to be, "if you don't use Dilivar the increased loading will exceed the mag case ability to hold the stud securely".
The statement is false. Plain and simply.
If your statement is that Dilivar will reduce the clamping force, I agree but my experience and that of many other professional builders is that Dilivar offers insufficient clamping force to produce the superior cylinder to head stability we desire for our engines as well as our customer engines.

[0396]

Originally Posted by Mark Henry

I went with Supertec studs on my build and a couple 930 builds, no leaks or issues.

I have a buddy with a 930 that sounds a lot like Tippy's, he used ARP and he's always complaining that his cylinders are weeping.
That said I have ARP on my Nickies type 4 engine in my '67 bug without an issue, but it's a 9.2CR N/A 180hp engine.

This is a very interesting tread. The comments of a few 930 build and the fact that there's no concerns with the Supertech studs are a little skewed. How many have been sold vs the amount of 911 engines that have had issues with the old design?
I'm sure the Supertech studs are a great product, but I tend to side with actual science and analytics.
Oh I have no skin in this tread...just my small brain thinking out loud.

[manbridge 74]

We tore down a 75S engine recently. It was a quite obvious we were the first to do so. I've got to agree with Henry about the heat comment as there was no front oil cooler and it had 150k miles. Oil control rings were carboned in place or it would likely still be in service. The case was perfectly straight.

Stud threads are the bestest.