Heads leaking. 993TT stud torque?
 

After a top end on my 87 930 with 98mm Mahle jugs and fully threaded 993TT head studs, I have head to cylinder leakage on 4 cylinders. The mating surfaces were checked before assembly and I used 25 ft-lb for torque. Is that the right torque for these studs and cylinders? I do not have flame rings.

When you re-torque, do you do one nut at a time, one cylinder at a time, or a whole side as if you were just reassembling?

Thanks,
Steve

How much boost and total timing are you running?

What fuel do you use?

With metal to metal sealing of the late Carrera and turbo spec is a 2step torquing
15 ft# then 90 degree torque angle.
Bruce

Stock .8 bar with conservative ignition. Max advance is 26 with 8 pulled back on boost. 91 octane pump gas.

Wastegate working properly? 91 is kinda short for your total timing as these cars were made for 93 or better. It becomes even more critical in hot weather. I would be running 22-23 degrees total with 91.

The reason I mentioned this is that detonation can make the heads lift and that can loosen head stud torque. I've never had any problems with the 993TT studs holding their torque, provided the wrench is accurate and the engine didn't detonate. This holds true for our 14:1 N/A engines as well as turbocharged ones at 1.2 bar.

Remember, you'll never hear it unless its bad.

Steve -- Sadly 91 is the best I can do where I live, but it's ethanol-free. Interesting thoughts on the timing. I've read tons of threads on that topic and I thought 26, 18 on boost, was pretty conservative, but I trust your experience. Are you saying 22 and still back out 8 on boost for a net of 14?

The top end refresh was the result of broken rings that I attributed to a bad boost retard pot on the dizzy, which I eliminated with an MSD programmable unit and locked dizzy.

Do you concur with Bruce's 15 ft-lb plus 90 degress for these studs? I did 17#, then 25# final, which I'm guessing is quite a bit lower than 15+90.

Thanks for you input.

Ethanol has an octane of 112 so that will not hurt at all provided the AFR's are correct. :)

You need more octane (on boost) or less timing so you maintain a margin against detonation. Twin-ignition is another good option for maintaining performance using reduced total timing.

Your broken rings was the "canary in the coal mine" here and one clue to the head stud issue.

I torque these initially to 15 lbs-ft, then 90 degrees using my Snap-on torque angle tool.

Yeah, 25#'s is not enough. You have to do the method described. I never checked what that torque roughly is, but it was far higher than 25#s.

Thanks everyone. Sounds like a detune, retorque and leakdown is in order. Hope my shiny new trueseal rings are still intact, they seated so nicely.

I'm still not clear on the timing numbers. 22 degrees at no boost or full boost? I'm running 26 above 2k with no boost and 18 at full boost. I've heard a lot of guys on the 930 forum talk of running higher advance than that even with CIS, single plug and pump gas. I'm not doubting your recommendation, I'm just not clear which number you are using.

I think the consensus has been 24 with 1 bar.

I know a top Porsche engine builder here in Florida that told me 36 ft lbs for the final torque when using the 993TT dilivar head studs in a turbo. I never tried that so I don't know how it would work in the long run.

I put ARP head studs in mine and the instructions said final torque should be 38 ft lbs with ARP fastener lube on the threads. They are not dilivar though. I think they are some kind of fancy stainless steel alloy.
FWIW, here's a scan of the intructions that come with ARP head studs that also shows the torque sequence.
http://forums.pelicanparts.com/uploa...1404312966.jpg

Thanks again for the help guys. I re-torqued using 15 plus 90 and they seemed to be sealed up nicely now. Ticks me off when I lose a day of my life because I did something wrong the first time!

Supertec head studs torqued to 32 lbs (for turbos) will offer far superior sealing and increased cylinder to head stability compared to any other stud on the market.