What are "stretch head studs"? (and other stud questions)

[Porsche_911s]

2.7 w/ 4.5k on most recent rebuild (case savers & normal 2.7 repair items) - Street car

I am toying with the idea of upgrading my pistons and cylinders when I change out my Cams. While reading Wayne’s book(s), I am going over all the new (or used) hardware for this type of procedure. While doing research on OEM, ARP or Raceware studs (trying to understand the difference), some of the information says that the OEM's are the "stretch" type that should be replaced with each rebuild. Does that mean they fatigue over time?

My rebuild was a budget rebuild, most parts were used and I am 90% sure my head studs were used steel head studs. If I decide to change the Ps&Cs, should I invest in new 993 steel studs or name brand racing hardware? If I decide to sell my 2.7 in the future, would name brand studs add value to the motor (assuming all is strong)?

If I change the 8.0:1 CIS Ps&Cs, I plan on going with 9.5:1 JE pistons. My RPMs normally do not exceed 5000 RPM. With the stock CIS internals, there is not much reason to go over 5k! Because I do not want to redo my heads, I don’t plan on going over 9.5:1 compression and will select an EFI Cam that the Camgrinder recommends.

[jmohn]

I think the correct term is "torque to yield" and, yes, such fasteners must be replaced not reused.

I don't know the answer to your other questions and I don't know if the original 2.7 studs were torque-to-yield or not. Hopefully someone else will answer.

Jerry M
'78 SC

[MotoSook]

The "stretch" or stretch gauge method of applying torque to rod bolts is generally applicable to .... the rod bolts. The rods bolt should not be re-used. I use ARP rod bolts when I rebuild engines.

The head studs are reuasable....I also use ARP head studs when I build high HP engines, but using steel studs (stock or 993-dilivar or 930-steel) is fine.

You should always inspect the parts, of course, so knowing what to look for is part of the task of rebuilding.

The stock (new) steel rod bolts for a stock rebuild is fine. I dare to say that even for a 3.2 with its reportedly week rod bolts! I use ARP rod bolts, because I am willing to pay a couple hundered dollars more for a strong foundation when I build my engines.

There are lots of options when building engines....not all are necessary and you have to know why before you buy or sign off on the build sheet. I go to great pains to explain the options to my clients. I want them to understand the limitations of the engine they want.

[Porsche_911s]

Thanks Souk!

And judging from what I will use the engine for & the fact the heads will be the next bottle neck, going with "racing" brand head studs might be over kill.

I have been reading thread after thread about what I am going to do or would like to do. I was getting confused with the different terms. I am asking questions now so I can start my budget. As others have pointed out, getting everything checked when it’s apart; I might find some machining costs that I did not anticipate.