Dilvar or Dilivar, whatever it's called.
 

Well, quite a while back i was questioning whether to take the advice of my former boss (owns a porsche shop) with the updated dilvars or go with steel studs. The whole thing of steel not expanding at the same rate as aluminum was bothering me too much, and since no one on the board seems to have tried the newer dilvar studs, i figured what the hell, i'll be different. Well just got them (unfortunately my engine stuff wasn't following it, but that's another story) and they look much different than anything i've seen. http://forums.pelicanparts.com/uploa...1069815794.jpg http://forums.pelicanparts.com/uploa...1069815832.jpg
And as a side note, i was talking to someone about some of the differences between say racewar, and these stock dilvar. Turns out that dilvar stretchs when you torque them to keep constant pressure (or so he says) on what it's holding, studs like raceware do not stretch at all and can be used infinitely. Because the dilvars are meant to stretch, they are not meant to be torqued down very many times before they must be replaced. That might be why some have broke because they weren't replaced. But anyhow, that's just speculation.

Well, not quite.

All fasteners are designed to stretch; that's how parts stay together when tightened to specs. I think you're referring to "torque to yield" bolts as used in 911 connecting rods and flywheels. These are designed to hold the correct tension once stretched to a certain torque value. However, at that point, they will almost take on a permanent stretch and thus are not reusable. This is not the usual case with head studs or most any other threaded fastener, otherwise you'd have to replace them every time you disassemble a part.

While ARP, Raceware and Dilavar are all made of high quality steel alloy, Dilavar is a special alloy with about the same coefficient of expansion as aluminum (the predominant metal in a 911 case, cylinder, head and cam housing). Dilavar is also non-magnetic (at least the earlier versions were). ARP and RaceWare will elongate like.... steel; which is not as nearly much as aluminum. However, they don't claim to, and they seem to work fine when used in place of Dilavar studs. Regular factory studs tend to as well.

You'll notice the last few versions of the Dilavar studs are coated in the middle. It is thought this portion of the stud is susceptible to the corrosive effects of exposure under the engine and why earlier thinly plated versions broke, or maybe it was due to substandard manufacturing QC. It seems Porsche also thinks Dilavar is most appropriate in this application, otherwise they'd have their own version of Raceware/ARP. The question is, "Will these latest Dilavar versions fit the bill?" Some who know better than I will say yes they will (I think) while others will go the ARP/Raceware route. I think the most appropriate material to use is something like Dilavar, but one that also doesn't break. I say go for it.

BTW, how much are these new versions? Let me sit down first.

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

And then there are those of us who took the tack of using good 'ol OEM steel studs (uppers), in place of Dilavars of whatever version. John Walker was among those who recommended this cost-effective method to me. Worked for my engine.

I took John's advice like Doug did. Head studs do not pull out of aluminum cases and OE steel studs virtually never break, according to some observers. When hot, I suppose they apply a little more pressure since the AL swells more than the stud. BFD.

Doug/Superman: It is not quite clear, did you use dilivar on the lowers, OEM on the uppers?

PBH I believe Doug and Super did what I am doing, use steel studs on the uppers and lowers. Fastred, the head studs in your picture are just like the ones I got. They are epoxy coated steel. Not dilavar. You can check them out with a magnet. Dilavar is non magnetic.

No, they replaced the lowers with steel, making them steel all around. And also worth mentioning, i don't know nearly enough about metalurgy to question some of the greats around here. I'm doing this because everyone on the board seems too scared to try the dilavars and since porsche still swears by them and there is yet another version of them, what the hell. Worst case senario, they'll be like the originals and take 20 years or so to try start breaking.
911pcars, the person i talked to about the dilavars was actually a 944 turbo tuner. Apearantly after torquing the studs down a number of times (4-5) they don't hold quite as well, and seem to permanently stretch. And he also told me that on his cars with steel head gaskets (my dad's 951) that they need more torque during assembly to keep them from leaking. Somewhere around 80 ftlbs is the final torque, where factory is 65 with the normal head gasket, and he said that he's tried but the dilavars won't hold that torque. But the racewares will. Dilavars might stretch in 44's since they have high torque values for there head, but this is just speculation as mentioned before.

From John Walker

"the 2.7 mag case, being softer and weaker than aluminum, is the only one that i would consider using diliver on, bottom row only, as opposed to steel studs. they are designed to match the expansion rate of the cylinders, and therefore will stress the threads in the case less than if you used steel studs."

I was planning to use dilivar on the bottom row of my 2.7 mag case, oem steel on the top.

This is driving me crazy, too many opinions, and I am still unsure after six months of pondering...

Any advice?

PBH, anything John says I would probably follow. For what it is worth, the dilavar studs on my 3.2 that I am replacing showed no corrosion at all. I was even giving thought to reusing them except that the steel studs are not that expensive. Hell you can even have my used dilavar studs to look at, use, whatever at no charge.

Are the "993" part # head studs dilavar? These are the ones that are threaded along the whole bolt.

Thanks Kurt. But I have 48 steel and 24 dilivar studs already.

I think I'll take JW's advice, steel uppers, dilivar on bottom row.

Weak Mg cases are not a concern for 3.0 owners, so upper & lower steel studs do the trick.

And on my engine, they do hold their tension.....I checked torque at 500, 2500, 5000, and recently, 7000 miles. I only had (1) stud to tighten about a *tiny* fraction of a turn, at 500 miles. Everything has been completely stable since then.

I'll repost this:

PEL-RTE-1022 Raceware Head Stud Set $499.95
901.101.172.03 Cylinder Head Stud-Early Steel $299.00
911.101.172.03 Cylinder Head Stud-911 2.7L Steel $248.40
930.101.170.02 Cylinder Head Stud-Dilavar $505.10
992.101.170.51 Cylinder Head Stud-993-Dilavar $603.90
993.101.172.02 Cylinder Head Stud-993 Steel $203.52

JP

I don't think they are that much, but i'll post after i get my bill from the shop.

These are PP prices for a set of 24.

Those studs look nice, all right! Steel is the way to go though IMHO. Sometimes the easy answer is the correct one. These new Dilavar things might just work fine, but so do the steel ones, according to many engine builders. The steel ones have more history in holding up okay, so that's what I'd use. I think once the mag case is fixed with inserts, it can take steel just as well too.

George

My car is going in for a rebuild probably at John Walkers shop. He noted that in the later years the dilavar is powder coated to prevent corrosion. The problem with the early dilavar is that it could corrode and weaken the stud.

It does look like something solid such as powder coating. As a matter of fact, a couple of them had some of the coating on the threaded area of the studs. Even running a dye over the threads it was still hard to get that crap off, i don't think these things are corroding soon.