Dilivar head studs on a 964 question
 

Hi all, I just purchased a used very low mileage 1991 3.6L 964 motor which appears to have epoxy coated dilivar head studs on all 24 head studs, (why not just bottom like the 3.2L?) my concern is should I replace them all? Is the epoxy coating sufficient to protect the studs from future snapping due to fatigue? or is it advisable to use 993 steel studs? I will not be racing the car but I will be installing ARP rod bolts. thanks, Johnny O

Ok this is only my theory but here goes

sc and carreras had bottom row dilivar and top row steel. The bottom broke first why I ask? Well because of different expansion rates something had to go.. Now 930's They had all 24 top and bottom dilivar did they snap well yes but not even close to as much as the sc and carrera and it was probably due to to much boost or corrosion on the studs.

So I do a top end on my 3.0 and it needed 24 studs. What did I buy ?? dilivar. Why? because if it was good enough to use them on the 930's it was good enough for me. But sometimes I do thing against logic


Thats said If I would have known what i was going to do to my engine when I did the top end I would have probably went ARP as there would have been no question but how often do you turn a NA 3.0 into a turbocharged 3.0?? With no internal mods?

Just food for thought. I will let you know if one ever pops on me

Good discusion here...the engine in question is a 930, but you'll get a feel for various head stud options:
http://forums.pelicanparts.com/911-engine-rebuilding-forum/294898-advice-head-studs-930-a.html

There will be lots of opinions on this one, but I used the 993RS,993tt, 993GT2 studs

24x 993.101.170.51

very reasonably priced, this is what the factory used on the race and sport models

factory rec is to [list=1][*]use optimoly HT 999.917.728.00 under the nut contact area
[*]pretighten bolts to 25NM, using X pattern, starting in the middle working to the ends(I can post the exact sequence if needed)
[*]unbolt completely in reverse pattern
[*]pretighten to10NM as in #2
[*]final tighten by 120&deg as in #2[/list=1]

Are the stock 993 studs reliable? I plan to leave the stock studs on my 95 3.6.

Sure, the fully threaded stock ones have been very reliable.

When I built my engine in the 90's, I used the black expoxy-coated Dilavar studs, top and bottom. So far so good. Knock on wood, cross fingers, etc.

During my casual observation of reported broken head studs since then, it seems most have been on versions used on SCs (yellow zinc plated) perhaps due to corrosion and a few black expoxed ones that were standard since '84 or so.

The different growth and contraction rates between upper steel and lower Dilvar studs coulld have contributed to premature breakage. Interesting observation.

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

Just finished a rebuild on an 88 Carrera due to 2 broken expoxy coated dilivar studs. The car has been stored winters, so no salt exposure. The engine had 88,000 miles on it. When it came apart the engine looked great. I reused the steel studs and put new steel in the bottom. If the budget had allowed I would have used the Supertec head studs. IMHO eventually all the dilavar studs will fail, just how long before it happens is the question.

again I think the key is if its 12 or 24 dilivar studs that is the factor.