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rod bolts and head studs question

Hi, I am rebuilding my 86 3.3 turbo engine I have read that engines like mine suffer from weak rod bolts and delavan head studs. I would like to hear your opinion about and recommendations about it. I would be also interested if you have something to offer.
Old 11-29-2010, 12:49 PM
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Supertec studs and ARP rod bolts.

Lindy
Old 11-29-2010, 01:17 PM
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Quote:
Originally Posted by ornas View Post
Hi, I am rebuilding my 86 3.3 turbo engine I have read that engines like mine suffer from weak rod bolts and delavan head studs. I would like to hear your opinion about and recommendations about it. I would be also interested if you have something to offer.
Just another opinion, especially for Turbo motors,....

ARP rod bolts and factory 993TT head studs. You cannot ever go wrong with that combination.
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Old 11-29-2010, 02:09 PM
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Originally Posted by lindy 911 View Post
Supertec studs and ARP rod bolts.

Lindy
Another vote for this combination. Superior quality over the factory pieces and the price of the head studs are a very reasonable.
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Old 11-30-2010, 07:44 AM
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I also went Supertec Studs.
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Old 11-30-2010, 09:32 AM
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My 400 hp 3.5 turbo engine was built with Supertec studs 5 1/2 years ago. No issues.
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Old 11-30-2010, 02:38 PM
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I know that the dilivar studs, as on the 993TT are supposed to have very similar thermal expansion coefficient to the aluminum cylinder heads. Does anybody know if this is true for the SuperTec studs?

If the thermal coefficients are different, what are the effects? How different can the two be before you have issues?

I think that if the cylinder heads are growing too much faster than your studs, that you will have geometry distortion in the cylinder since it is being constrained by the studs. This is just theory of course, but isn't it a typical engine machine procedure to deck-plate the cylinder on final hone to simulate stresses induced by the head studs? That way the cylinder is perfectly round when you bolt the heads on. This is for American V8s anyways.

PS.: Turbpro, your setup looks very interesting. I'm doing some light research on turbo motors. I will have to search and hopefully find your engine project.

Last edited by AlfonsoR; 12-06-2010 at 01:35 PM..
Old 12-06-2010, 01:33 PM
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TTBOMK, expansion rates were matched to prevent studs from pulling out of the case. I doubt there is much deformation going on in the cylinder roundness based on the cylinder wall expanding at a greater rate that the stud holding it to the case. Henry can tell you in great detail the effects of all of this.

Lindy
Old 12-06-2010, 02:37 PM
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The reason why Dilivar was utilized was to control a specific problem during cool down. The lower studs would not cool as fast as the cylinders. If you drove the car during this transitional period without warming up the motor there would be some movement and some wear at the sealing suface. Porsche, like other manufacturers have to deal with customers that do not really know how to drive and maintain their products.

Some may say that the studs are for proper torque at temp, but one can calculate what the clamping pressure will be for any material at the engineered temp. In fact Porsche has done it for you already. The stud torque specifications are 14 ft/lbs less than a standard 10mm.

Running Henry's head studs are fine. There has been no complaints of failure and there has been no signs of damgage to high mileage motors when they were disassembled.
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Old 12-07-2010, 11:48 AM
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Quote:
Originally Posted by BURN-BROS View Post

Some may say that the studs are for proper torque at temp, but one can calculate what the clamping pressure will be for any material at the engineered temp. In fact Porsche has done it for you already. The stud torque specifications are 14 ft/lbs less than a standard 10mm.
.
I am not following your statements...

You can calculate the clamping force for the dilivar then calculate the torque or stretch for another material, but that is not what I am talking about.

A different application, but In the design of vessels and their flanges, you also select bolting material to have similar thermal expansion coefficient to the vessel material. The reason for this, in case I did not make myself clear, is that you want the vessel, the flange and the bolting material to grow and contract together at a similar rate during thermal cycles. Otherwise, you will eventually have a leak.

Or maybe you are saying that thermal expansion rates don't matter?

If you are having good success with SuperTec studs, then I would say continue using them, sometimes theoretical discussion are just that, and the "real world" says something different.

On the otherhand, I haven't heard of any 993s, NA or Turbo, have head stud failures. Have you?
Old 12-07-2010, 02:17 PM
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Everything I read about the new 993 stud is positive. I think the price is the only thing preventing an A+ rating from some. Evidently, thermal expansion rates while heating and at running temperature are not of concern. It's the cooling process that allows the clamping pressure to be reduced on the bottom studs and if the motor is restarted during the cool-down and run hard, it can produce leaks at the head/cylinder joint.

I designed pressure vessels for a time and finding materials with similar expansion rates was near impossible. The answer was to over-build and compensate through large safety margins. Where a 1" flange would work on paper, a 2.5" flange was fabricated to absorb the unknowns. I think the Supertec stud uses some of this design theory.

Lindy
Old 12-08-2010, 06:02 AM
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.....snip.......

On the otherhand, i haven't heard of any 993s, na or turbo, have head stud failures. Have you?
yes!!!

To date, no customer has ever reported an issue with the Supertec studs. To date, I have not read one negative critique of the Supertec stud by anyone who has ever tried them. I see a lot of criticism from people who have never even held one in their hand.
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Last edited by Henry Schmidt; 12-08-2010 at 06:40 AM..
Old 12-08-2010, 06:34 AM
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Exactly!

Quote:
Originally Posted by Henry Schmidt View Post
yes!!!

To date, no customer has ever reported an issue with the Supertec studs. To date, I have not read one negative critique of the Supertec stud by anyone who has ever tried them. I see a lot of criticism from people who have never even held one in their hand.
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Old 12-08-2010, 08:20 AM
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I am not following your statements...

You can calculate the clamping force for the dilivar then calculate the torque or stretch for another material, but that is not what I am talking about.

Some people continue to post that Dilivars were used to help with pulling head studs.


Quote:
Originally Posted by AlfonsoR View Post
A different application, but In the design of vessels and their flanges, you also select bolting material to have similar thermal expansion coefficient to the vessel material. The reason for this, in case I did not make myself clear, is that you want the vessel, the flange and the bolting material to grow and contract together at a similar rate during thermal cycles. Otherwise, you will eventually have a leak.

Or maybe you are saying that thermal expansion rates don't matter?
I am saying the if a porsche owner properly warmed up his/her car before attempting the mad rush back to work after lunch, the thermal expansion rate does not matter. And if you did not, it does not matter much.
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Old 12-08-2010, 10:26 AM
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Originally Posted by lindy 911 View Post
Everything I read about the new 993 stud is positive. I think the price is the only thing preventing an A+ rating from some. Evidently, thermal expansion rates while heating and at running temperature are not of concern. It's the cooling process that allows the clamping pressure to be reduced on the bottom studs and if the motor is restarted during the cool-down and run hard, it can produce leaks at the head/cylinder joint.

I designed pressure vessels for a time and finding materials with similar expansion rates was near impossible. The answer was to over-build and compensate through large safety margins. Where a 1" flange would work on paper, a 2.5" flange was fabricated to absorb the unknowns. I think the Supertec stud uses some of this design theory.

Lindy
Right on!
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Old 12-08-2010, 10:28 AM
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Ok, color me slow...

I follow that improper cool down can have the cylinder shrinking faster than the stud and a leak occuring... but how do you get that situation leading to a pulled stud? Non corroding steels typically have a lower thermal transport than aluminum (forged or cast), so the aluminum is going to dump its heat faster and return to orginal size faster. that should leave the stud loose, not put the stud in enough tension to pull the base magnesium.

I must first say that I chose Henrys studs ready to go for my 2.8 hot rod build as well... but I do have to say that untill his studs see the use numbers that the 993 divlar stud has been applied, its apples and oranges.

Vioxx was all great until the 'test population' got large enough to make the outliers come out of the noise. Large populations tend to show hidden things.

t
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Old 12-08-2010, 01:06 PM
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I will say that our sample is nowhere near the 993 Turbo sample, but we have sold over 1000 sets during the 8+ years of testing.

As for the studs issue on cool down: The mid seventies 2.7 were the engines that experienced the stud pulling problem the most and if you remember those cars were thermal reactor cars. The 1800 degree cans directly under the cylinders actually caused the cylinder and head temps to go up after the engine was shut off. I remember seeing the asphalt glow red at night when these the engines were shut off. This excessive heat on the bottom of the cylinder without the benefit of cooling (fan) air is what caused most of the damage.
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Old 12-08-2010, 01:45 PM
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Ah! The dreaded thermal reactors. Understood. I assume the same horrific temperature imballance observed on the 993 and 993tt which is the current use of divlars or do you think its a case of 'too much invested not to use'?

One thousand sets is an impressive number for a custom part, and hopefully a very nice profit number if your margin is typical of retail items. Good products should (sometimes, not always) be rewarded with sales.

t
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Old 12-08-2010, 02:43 PM
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Profit ? "we don't make no stinking profit!!!!!"

We built these studs because everything else on the market made no sense.
I would much rather buy a product I want for my rebuilds than try and reinvent the wheel. Problem is, the old wheel sucked.
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Old 12-08-2010, 02:54 PM
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Henry... If your saying you pulled a Dr. Salk and you sell your studs at cost I'm gonna have to call the local liberitian chapter to come get your membership card. LOL!

t
Old 12-08-2010, 03:35 PM
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