Pelican Parts Forums - Rering or salvage?

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OK, i have a question about head studs. I know the obvious, steel good, dilvar bad, racware hella good. Now whenever i buy parts, i get things like this from my old boss in Jersey. He told me that for replacement head studs, they've always used USA dilvar. According to him, european dilvar are the ones that get brittle and crack. But usa dilvar in 911 motors does not. Does anyone know what the hell he's talking about, i've always trusted him and never been steered wrong, but this sounds a bit odd. And BTW, their primary specialty are 911's.

Here's what I know. Dilavar is what Porsche uses in their head studs, not Dilvar, Dilivar, Divilar or any one of several like-sounding names which may or may not (probably not) have the same structural composition and strength as Dilavar.

According to Forbes Aird's reference book, Racer's Encyclopedia of Metals, Fibers and Materials. Dilavar is a trademarked name owned by a German company, Thyssen Edelstahlwerke. While having about the same thermal coefficient as aluminum and magnesium and with similar expansion characeristics, it has an ultimate tensile strength (UTS) of 180 ksi (that's pretty strong).

I believe in the stuff, maybe because I installed them in my 2.7 a few years ago and they haven't snapped yet. So far, so good. FWIW, most of the Dilavar studs that seem to have an abbreviated life span are the silver and gold colored versions used up until around '84. And these seem to die due to unprotected exposure which results in corrosion. The black epoxy versions used in my engine don't seem to fail as regularly.... I think (hope). Knock on wood.

I would check their spelling and let us know.

Sherwood Lee
http://members.rennlist.org/911pcars

I'm not positive, haven't talked to him in awhile, but i didn't know that there were different dilivar's. Or dilivar, dilavar, dilvar, or whatever. I do remember being told off the top of my head that raceware studs are like 190,000psi of tensile stregth which is sick. If your dilavar studs are as strong as you say, then i'd think that they are pretty bada$$ and wouldn't worry. I'll give them a try anyway, Mike (my old boss) has never steered me wrong. Besides, my dad's 951 has the same studs he's talking about and the little ***** puts out about 350 at the wheels with 18 lbs on a stock k26 cup turbo. Those Tech 2's are cool, let me tell you.

I don't know much about Raceware studs but if their coefficient of expansion isn't similar to Aluminum I would hesitate to use them, no matter how strong they are. Anything will tear it self apart if the coefficient of expansion isn't close enouth for the operating temperature range and within the strength of the fastener and what the fastener attaches to. I would use steel studs with steel cylinders, Dilavar with Aluminum cylinders. If Raceware has studs that match the coeficient of expansion of Dilavar, or is within the same range I would use them with Aluminum cylinders, as they are likely stronger. If not I would only use them with steel cylinders or cylinders with a similar expansion rate.

My experiences with military stuff, operation temp range of -55C to +125C is that the mismatch of the coeficient of expansion needs to be about 40% or less. If its within this range it will last indefinitely. If it is not, e.g. say 3:1 like steel vs Aluminum, it will likely break within 30 or 40 temperature cycles. The closer the match the more cycles required to break it.

For whatever its worth.

Snowman,
Damn, I would have to agree with you in terms of matching the expansion rates of studs and cylinders, yet Raceware and ARP head studs, they being merely very strong studs with no special expansion characteristics, seem to work in this application. I haven't heard of any reported compression, head gasket, pulled stud failures on this or other pcar forums..... yet. How long have they been on the Porsche market, 3 years or so? Maybe time will tell.

Sherwood

Unfortunately it takes a lot of samples as well as cycles to spot trends that are not obnoxious. Time will tell.

From my archives...

Quote:

Subject: Re: RACEWARE - Technical Misunderstand - Again !
From: "Randy Hubbard" <raceware@wwnet.net>
Date: Mon, 25 Oct 1999 12:48:08 -0400
X-Message-Number: 60

I'd like to again correct Mr. Bishops post to the list and answer some other question presented.

Mr. Bishop please do not take my comments out of context to support your beliefs. I did NOT agree with you on your statements concerning thermal expansion and service data. I specifically stated that the RACEWARE Head Studs are made from an Aerospace quality material and that we have modified the stress/strain relationship of the stud to provide the correct clamp
force when the 911 engine is cold all the way thru the operating range tomax temp. I also indicated that with over six years of service data we have never had a single failed RACEWARE 911 Head Stud nor engine, which is something Porsche can not say about the Dilavar studs.

These are the FACTS Mr. Bishop:

Dilavar Studs - History of fractures in NEW studs, Porsche on 7th or 8th stud design, Porsche discontinued ALL Dilavar stud use prior to 993 engines.

RACEWARE - ZERO FAILURES in over 6 years of use by thousands of people World Wide

BTW, it only took Porsche two years to realize the magnesium case and various iterations of the Dilavar studs were constant problems. For the record Porsche DISCONTINUED all use of Dilavar studs with the 993 engines.
So it's pretty clear Dilavar is not the savior it was hoped to be. If
however you believe that Dilavar is the best choice for your engines, by all means feel free to use it. I must insist however that you do not make misinformed statements concerning the RACEWARE 911 Head Studs as this would disparage our superior product which has served Porsche owner's and engine builders very well for many years.

On to other questions:

Tom Frisardi mentioned an incident on a 2.7L engine he disassembled years ago that had deep grooves in the heads. Mr. Frisardi theorized the steel studs in that engine caused the deep grooves, most noticeably on the exhaust side of the head.

Mr. Frisardi in our experience the situation you described is not caused by excessive clamp force from the steel head studs, though that is a reasonable assumption. In reality it's quite likely the grooves you witnessed were the result of insufficient clamp force. Allow me to explain. When combustion occurs in the chamber it propagates from the hottest part of the chamber to
the coolest area of the chamber. Thus combustion starts around the exhaust valve and works toward the intake side of the chamber where the cool mixture has entered. The pressure rise is very high at the beginning of the combustion process as the piston is at top dead center(TDC) and beginning to descend in the cylinder as combustion continues.

The rapid pressure rise in the chamber on the exhaust side of the chamber can actually force the head to "lift-off" if there is insufficient clamp force. Once the head lifts up a small amount pressure is relieved as blow-by and the head slams back against the cylinder surface. This can happen as often as 60 times per second in a high rpm engine like a Porsche 911. This is very much akin to how a jack hammer or zip gun used for muffler repair cuts. The high frequency lift-off of the cylinder head and then the slamming back down against the cylinder literally pounds a groove in the head.
With the proper clamp force these grooves do not occur. We have designed the RACEWARE Head Stud accordingly. Excessive clamp force from an improperly designed head stud doesn't cause the grooves you saw. Excessive clamp force bends the heads and cracks the top of the cylinders. It's real easy to distinguish what the problem is when you know what to look for. So in the case of the 2.7L engine you examined years ago, the damage could have been prevented by having the correct clamp force which the OE Porsche steel stud could not provide. The reason RACEWARE studs have been so successful is because they work properly by design and provide the correct clamp force.

To "Flat 6 Bruce":

As illustrated above the Porsche steel head studs do not have the ability to provide the correct clamp force nor do hot rod aftermarket studs which can exhibit excessive clamp force. Race-Tech Engineering, Inc. spent two years in the design and development of our 911 RACEWARE Head Studs because we were
determined to find the proper solution to head leaks in the 911 engine.

If you thermally map a 911 engine you will find that the cylinders do not all run at the same temp. You will also find the head studs do not operate at the same temps, nor do they operate at the same temp as the cylinders.
Porsche's attempt to bandaid the magnesium case was a good idea gone bad from our perspective and we are strong Porsche enthusiasts and have great respect for Porsche engineering.

Race-Tech took a different approach to sealing the 911 engine because it's impossible to control the thermal variations in these engines. This is the reason Porsche was forced to change to a water-cooled design in later years.
Instead of using an alloy with a thermal expansion similar to the aluminum cylinders, we used an Aerospace quality material that would allow us to alter the mechanical properties so that there is proper clamp force both cold and hot. This was BY DESIGN and it's the reason why no other 911 Head Stud performs like a RACEWARE Head Stud. I can not disclose proprietary engineering and design info. but the results speak for themselves.

Bottomline, the RACEWARE Head Studs deliver maximum performance AND reliability without over-stressing the 911 engine case or heads. You might be interested to know that magnesium alloys used for engine cases actually fatigue with time and heat cycles. The only reason magnesium was ever considered was for weight but it was a bad decision none the less.

Regards,

Randy Hubbard, '90 Carrera 4
Race-Tech Engineering, Inc.
http://www.wwnet.net/~raceware

Common consensus is that the early studs are very effective for any engine 1965-89. They have proven themselves over the past years when they replaced the Dilivar studs.

-Wayne

Wait, now i'm a little confused, are the OE studs dilivar or dilavar or something else? Besides the steel ones that is.

Quote:

Originally posted by Wayne at Pelican Parts
Common consensus is that the early studs are very effective for any engine 1965-89. They have proven themselves over the past years when they replaced the Dilivar studs.

-Wayne

The "early studs" refers to the early steel studs.

RaceWare is the good, golden upgrade, but not necessary for everyone.

-Wayne

Does any one have any experience with the supertec stud? They are stainless steel, heat treated , etc... I don't have the full specs. They claim superior performance and good torque propeties due to m10x1 threads at the head.

Thanks,

Arnie

OK, in case no one saw the update on the technical forum. In a nutshell, oil ring cracked, cylinder fin crackes, me is screwed!

Assuming i attempt a rering, the rings i'd use, are they the same for ausil and nikasil? In other words, the ones on the pelican rebuild wizard page, would these work with my ausil's?

Only thing I heard was not to use the famous Deves (sp??) rings. Something about to much tension and not enough use of gas pressure to seal with. Thats what an old guy who has been machining Porsche engines for almost as long as Porsche has been around told me. His name starts with a Bech?? but I can't remember it exactly

Would that be Bieker? If so, http://www.biekerengineering.com/

Sherwood

What about the rings that wayne sells, are those safe?

Quote:

Originally posted by 911pcars
Would that be Bieker? If so, http://www.biekerengineering.com/

Sherwood

Yep.

While he was in Burbank, Bieker performed most of the machine work on my engine. Very good machinist. I learned alot from him.

Sherwood

Well, i guess rering it is, wish me luck (and between the motor, trans, and cis wiring, i'll need it)!

Can someone send me a pm on how to post pics? I'd like to post some pics of the car and the progress of the motor/trans but don't know how to (or at least never tried).