930 head stud choice

[ken martin]

I've seen alot of traffic on head studs ..what is the cocensus on the right head studs for a '78 turbo?

thanks

[Steve@Rennsport]

FWIW,

The only studs we use on Turbos are the late 993 TT ones. These are the latest Dilavars and best handle the expansion rates that 930 engines have.

I've had too many of the ARP/Raceware ones loosen up when hot.

Steel studs, while quite strong, do not allow the expansion that Dilavars do and Turbo engines really grow under boost. This makes the heads more prone to leak from distortion.

Just one opinion though,.....

[350HP930]

Ditto here. I got a set of 993 TT studs sitting in a box waiting for my rebuild to progress.

They only ended up being about $7 a piece after my employee discount.

I trust ARP and Raceware to know how to make a good rod bolt or head stud for a water cooled motor but I leave it to porsche to know how to make the best head stud for an air cooled motor.

[Wayne 962]

It's probably okay to go ether way. The newer studs are supposedly better, but then again, the older Dilavar studs didn't break for many years, and then succumbed to corrosion...

-Wayne

[carmad]

I went with the 993 studs, for most of the reasons previously stated.

[Porschephd]

What is interesting is we have seen about 45 993TT motors and not one had dilavar studs in them. They are standard steel studs. Also the last 5 3.6 single turbo motors I built didn't have dilavars either. All of theses were low mileage virgins. Bruce and I were talking about this last summer. He saw the same thing at the factory. I do not use Dilavar in any motor any more. We have seen a few cases where motors done less than 5 years ago with the new "993" stud have already broken. Raceware and ARP are the best thing going. We have no issues if loctited properly. We have some motors that have been running ARP and Raceware for many years and gone back in. No evidence of issues with these type of studs if install and torque settings are followed. BTW the motors were apart because people catch this thing called the HP bug Hope this helps.

[viejopatron]

I'm rebuilding a 3.0 with a broken exhaust side stud so I'm interested and motivated on this subject. I've worked design of aircraft flight controls and I can tell you that the big items to check on parts subject to hot and high tensile cyclic loads are; material, design, processing and installation.

I can go to the ARP site and learn something about the material properties which I can't do at the Raceware site. I can look at a part and search for sharp-ish corners [internal and external] that are stress risers. I can also look at the machine finish [can you see your reflection?] If an engine stud was for aircraft use, it's finish would be an 8 micro-inch or less [a "mirror" finish is considered a 4 or less]. Is the material subject to hydrogen embrittlement and if so, was it processsed [usually baked] after heat treat. Was it magnetic pentrant inspected at final?

I do not know how much of this is done by the automotive suppliers, probably some bit of all the above. Maybe a sample from each lot. I plan on doing as much independent checking as I can. Some may think that's crazy, however I be really PO'd to have a stud F**k me because it had a propagating crack as-purchased.

Lastly, I've seen plenty of part installations that were "mortally wounded" by being damaged at installation. These cases acted as time bombs needing only a few cycles to fail. I plan on going real slow.

[Wayne 962]

Like universal health care, peace in the Middle East, and all other questions in the Universe - this will be debated endlessly with no definitive conclusion...

-Wayne

[Porschephd]

Agreed....There may be something better out there, but for me these have worked. The others have broken. I hate mistakes so try to avoid them at all cost. Of course having a head lift is never any fun either when making gobs of HP

[Superman]

Wayne, most of those political debates are over. I'd be happy to outline the winning ideology if you wish.