Headstuds - would you use these?

[Steve@Rennsport]

Originally Posted by K24madness

Does anyone know if the 993NA and the 993TT share the same studs? Any concern about reusing a set that has 29k miles?

They are not the same. The 993TT, 3.8RS and RSR all use a different stud and those are ones we use in all 3.0 or larger engines.

[K24madness]

Originally Posted by Steve@Rennsport

They are not the same. The 993TT, 3.8RS and RSR all use a different stud and those are ones we use in all 3.0 or larger engines.

Thanks Steve!!

The head stud topic is one of those rare cases where the camps are so far divided. It leaves me scratching my head. Many stories of success or failure (except supertechs) of ARP, Raceware and factory 993tt dilvar. I will have to err on the side of caution and engineering principals and go with the 993tt studs. My last 993tt put down 600tq x 600hp on a stock motor and the heads never leaked. My current project will have less cylinder pressure so the stock 993tt studs should prove good.

I would love to hear more from the big (800hp+) turbo builders on their thoughts.

[Geronimo '74]

I'm doing a rebuild (3.2 with some mods)
Al things considered, I'll be ordering Supertec studs instead of 993 full threads. Even if one is better than the other, I'm quite sure that both kinds are more than capable of performing the task I want them to do. (holding heads, cilinders and case together)
After hearing a lot of good things about Supertec and the fact that they come as a complete package (studs, bolts,...), for a very reasonable price.... I'll be ordering Supertec studs for my engine.
If I had 993 studs already lying around.... that would be a different matter.

[racing97]

When is the last time the Porsche head studs were prone to breakage the early 80's

regards

[Henry Schmidt]

Originally Posted by Steve@Rennsport

They are not the same. The 993TT, 3.8RS and RSR all use a different stud and those are ones we use in all 3.0 or larger engines.

Steven
I get a kick out of your passion for such a silly stud.
If nothing else you must admit that the stud design strains credulity. Stress risers in the middle of the stud should give anyone reason to think.
The key seems to be this notion that Dilavar expands with the same (similar) rate as aluminum. I have check ad infinitum and can't for the life of me find any specs on this magical expansion coefficient.
Since no one seems to know (unless you have this number) what the expansion rate is how do you know that it expands at a better rate than Supertec studs ?
For that matter any stud? Please enlighten me.


Could it be that the material in my stud is just too expensive for the Porsche bean counters?
If they had a choice with no regard to price would they use my design instead?

Of course you can't answer these last question with any certainty but it's fun to ponder the question anyway.

[Henry Schmidt]

Originally Posted by racing97

When is the last time the Porsche head studs were prone to breakage the early 80's

regards

Well into the 90s hence the need for constant upgrades.

[Tom F2]

What's silly about this discussion is that it misses the main point, Porsche switched to Dilavar because the difference in thermal expansion rates of aluminum and conventional steel studs proved to be too much for the CASTINGS. 911 motors with cast iron cylinders do fine with conventional steel studs.

Take a look at the cylinder heads on a 2.7 with pulled studs. The cylinders will have pressed so hard against the sealing surface that they make an impression which must be machined away to restore a flat surface.

I don't believe that the factory steel studs ever break, so why spend the money for the fancy Raceware, etc., which have the same thermal expansion rates? (I called Raceware and asked.)

So, if you want to get a long life out of your head and crankcase castings, you'll go with Dilavar. If you just want to have a nice set of intact headstuds for a long time, you'll go with steel, factory or aftermarket.

300 engines Henry? That's what Porsche makes in a week. Oh, and they do have a few good engineers and a bunch of laboratories to test all this stuff. And they deal with warranty issues all day long, everyday.

That said, the thermal reactors really were a disaster.

[Henry Schmidt]

Originally Posted by Tom F2

What's silly about this discussion is that it misses the main point, Porsche switched to Dilavar because the difference in thermal expansion rates of aluminum and conventional steel studs proved to be too much for the CASTINGS. 911 motors with cast iron cylinders do fine with conventional steel studs.

Take a look at the cylinder heads on a 2.7 with pulled studs. The cylinders will have pressed so hard against the sealing surface that they make an impression which must be machined away to restore a flat surface.

I don't believe that the factory steel studs ever break, so why spend the money for the fancy Raceware, etc., which have the same thermal expansion rates? (I called Raceware and asked.)

So, if you want to get a long life out of your head and crankcase castings, you'll go with Dilavar. If you just want to have a nice set of intact headstuds for a long time, you'll go with steel, factory or aftermarket.

300 engines Henry? That's what Porsche makes in a week. Oh, and they do have a few good engineers and a bunch of laboratories to test all this stuff. And they deal with warranty issues all day long, everyday.

That said, the thermal reactors really were a disaster.

Sorry my friend, (IMHO) you missed the point.
Dilivar is a horrible material that never should have been used in automotive application.
Porsche made a mistake. This is not unprecedented.
Over the years they have made many mistakes (once again, IMHO) and what they planned for the Dilivar studs and what happened in the real world is miles apart. It's one thing to claim similar expansion rates and an entirely different thing to prove that their expansion coefficient is the correct one in real world application.
As for your theory about 2.7 head damage, the stud is not the problem, Heat and the inherent weakness of the mag case is.
When properly inserted and with heat under control, even a stock steel stud will offer adequate service.
The question is "wouldn't you rather have better than adequate service?"
There is a better choice but it requires that Ostrich like behavior be set aside.

[K24madness]

Originally Posted by Henry Schmidt

Sorry my friend, (IMHO) you missed the point.
Dilivar is a horrible material that never should have been used in automotive application.
Porsche made a mistake. This is not unprecedented.
Over the years they have made many mistakes (once again, IMHO) and what they planned for the Dilivar studs and what happened in the real world is miles apart. It's one thing to claim similar expansion rates and an entirely different thing to prove that their expansion coefficient is the correct one in real world application.
As for your theory about 2.7 head damage, the stud is not the problem, Heat and the inherent weakness of the mag case is.
When properly inserted and with heat under control, even a stock steel stud will offer adequate service.
The question is "wouldn't you rather have better than adequate service?"
There is a better choice but it requires that Ostrich like behavior be set aside.

Henry I don't doubt that you make a high quality head stud. Is it better than the latest factory Divilar? Yes and no in my opinion. I think there are trade offs with each and one has to choose what he/she thinks is the best compromise. I also think the applications for the Porsche motors are so broad there is no one best answer.

A good question to ask is why did Porsche keep coming back to the Divilar material after switching to steel?

I know from my experience with air cooled aluminum Harley motors using steel studs the heads can leak when cold. It's not till the motors reach operating temps the heads are fully torqued due to the differences in the expansion rates of the materials. I have seen more than one guy blow head gaskets because they beat on the motor when it was cold.

[Henry Schmidt]

Originally Posted by K24madness

.....edit..... I think there are trade offs with each and one has to choose what he/she thinks is the best compromise. I also think the applications for the Porsche motors are so broad there is no one best answer.

A good question to ask is why did Porsche keep coming back to the Divilar material after switching to steel?

Why did they keep building air cooled engines when everyone knew the superiority of water cooling. Because they could get away with it?

I'll bite, what are the trade offs. If you're going to elude to some mystic expansion coefficient, please list it.
I have the numbers for my stud and can verify the expansion coefficient.
Now my questions: What is the expansion rate for Dilivar and why is it better that the Supertec stud?
These are simple questions that seem to get dodged constantly. This is a simple exercise in logic. Use whatever stud you want but if "you" plan on making claims be ready to back them up.
I believe my stud is better because it offers design superiority: Torquing a fine thread nut offers more accuracy. All thread is goofy in that it leaves two stress risers in the middle of the stud. Allen nuts strip and seize on Dilivar stud do to corrosion and electrolysis from the proximity of heated, dissimilar materials. Dilivar studs require a very accurate installation height where as Supertec studs do not. This allow Supertec studs to employ complete thread engagement in the case. 12 point nuts far superior in quality to stock Porsche head nuts. Higher grade is the criteria I use to make this claim.
Supertec head studs will never corrode and never break.
Earlier someone asked if they should "reuse a Dilivar stud"? If you believe a Dilivar stud can be reused, I have a butch for sale. I aim to please so come and get them. I'll sell them for 25% of the best new price you can find. Hey Steve, here you go. Great studs at a great price!!!

[dshepp806]

+1, Henry!

[911 tweaks]

Henry knows his sh^t... why do some keep hammering on questions is beyond me...

[jcge]

Originally Posted by Henry Schmidt

...edit... If you're going to elude to some mystic expansion coefficient, please list it.
I have the numbers for my stud and can verify the expansion coefficient.
Now my questions: What is the expansion rate for Dilivar....

According to Mezger's 1972 IME paper - the coefficient for Dilavar is "approximately" 20E-6/°C

Also one important bit of companion info from the same reference, that is rarely acknowledged.....
"In addition the cylinder head bolts (edit....uncoated Dilavar...)are insulated by fibreglass, otherwise the cooling air flow would cause the temperature level of the bolt to fall far below that of the cylinder."....think cold engine moisture trap and corrosion cracking...

And from BA's Performance Handbook (p77) - Dilivar 20E-6/°C

"Specification of Dilavar as manufactured by DEW, Krefeld (edit...Deutsche Edelstahlwerke...) are as follows:

Carbon 0.065%
Silicon 0.200%
Manganese 5.000%
Chromium 3.500%
Nickel 12.000%
V+FE 78.650%"

No datasheet is forthcoming on the DEW website.....perhaps a proprietary or customer specific alloy....(I doubt they'll respond for my request for one, but time will tell)

Did a search of German patents and trademarks, but no hits on Dilivar or Dilavar...

John

[jcge]

All that aside, surely its not too hard to actually measure the expansion coeficient....a stud about 150mm long - more than enough gauge length to measure a change over about 100°C or so.

Henry - do I have this right for the Supertech studs.......1365MPa YP and 1462MPa UTS ??? now that's quality steel !!!!

John

[WERK I]

Originally Posted by 911 tweaks

Henry knows his sh^t... why do some keep hammering on questions is beyond me...

Because there are other knowledgeable 911 engine builders out there who happen to disagree?
Just a guess.

It used to be that you could get the 993TT head studs at a pretty good price. Now, the price of those studs has nearly doubled ($35-$40 ea.) over the past 5 years making it the most expensive solution of the choices out there. Price vs. performance is no longer a consideration.

Bottom line, it's your engine and your money. Consult with multiple reputable builders out there and go with it. You've heard from a couple, Henry (Supertec) and Steve (Rennsport) and they happen to disagree. Both are very reputable builders.

[Henry Schmidt]

Originally Posted by jcge

All that aside, surely its not too hard to actually measure the expansion coeficient....a stud about 150mm long - more than enough gauge length to measure a change over about 100°C or so.

Henry - do I have this right for the Supertech studs.......1365MPa YP and 1462MPa UTS ??? now that's quality steel !!!!

John

Thank you for posting the expansion rate for Dilivar. It's a number that I struggled to find (shows I'm not perfect) .
Your suggestion about stud length when heated has no tangible value unless an equally accurate measurement can be made of the cylinder it holds. As I understand it (I'm a mechanic not an engineer) cylinders have different linear expansions rates but most cylinder manufacturers us high silicon content in their cylinders to prevent or at the very least reduce linear expansion.
I would think your experiment would be of value from a researchers point of view but from a practical point of view, I believe that the difference between expansion coefficients is a minor issue at best. That's why my question was formed in two parts "What is the expansion rate for Dilivar and why is it [that rate] better than the Supertec stud?
I have been evaluating & debunking Porsche myths for years in order to build a better/ more cost effective product.
Just like the myth of boat tailing, the difference in expansion rates of studs is of little or no consequence in the function of a 911 engine.

[Tom F2]

Hi Henry,

Here's the answers. I think that it is clear why the steel studs worked with iron and biral cylinders in the old 911s, and why Dilavar would be helpful where purely aluminum cylinders are used. These are linear coefficients, which should be the figures to use to determine the changes in clamping force on the heads.

Material/ Coefficient of thermal expansion (10E-6/C)

Aluminum/ 23
Steel/ 11-13, depending on alloy
Iron/ 11
Dilavar/ 20

By the way, I'm a big admirer of your work!

Tom

[K24madness]

Originally Posted by WERK-I

Because there are other knowledgeable 911 engine builders out there who happen to disagree?

Bottom line, it's your engine and your money. Consult with multiple reputable builders out there and go with it. You've heard from a couple, Henry (Supertec) and Steve (Rennsport) and they happen to disagree. Both are very reputable builders.

Both are very reputable and both had success using different approaches.

The expansion and contraction rates for dilavar and aluminum are close BUT do they run at the same temp? As Henry pointed out the cylinders are high silicon so standard aluminum expansion rates don't apply.

Because of the success of each has had (and other I have spoke to) with the two different materials this is one of those cases where there is no clear cut best answer.

[jcge]

Henry - acknowledge your question was asked in two parts - and I only tried to contribute some "factual" info on the first part re material property.

I was only suggesting the coeficient of the Dilivar stud (alone, in isolation) could be simply measured to get an actual value (vs published or quoted number) - not the whole head,cylinder,stud,case system...

But on that note, foil strain gauge, on a stud(s) , on a dyno, would tell you what s happening.

John

[svandamme]

So how about getting some real life measuring done?

Thermal expansion
- Supertec studs
- 993TT, 3.8RS and RSR studs
- regular steel studs
- a Nikasil Mahle barrel
- a Nickie barrel

And then follow up with a strenght test of the studs with their respective nuts and specific fitting instructions (threadlockers / no threadlocker).

Sure it's no massive test that simulates years of use and many many heat cycles..
But the raw strenght and expansion values of new studs should at least make for some kind of comparison that isn't about "he said that , but i say this, and the other guy is wrong"

It's all mechanical, so it can be measured, right?