993 Head studs, two types?

[WinRice]

Originally Posted by Weissach911

The preload in an M10 x 1.5 fastener torqued to 26 lbsft would be around 5250 lbs assuming that threads were lubricated.

This would result in a clamping force of 21000 lbs when cold and would mean that the joint could stand a peak cylinder pressure of about 1900 psi before it lifted.

Clamp Force increase (when warm)

17-4PH 13500lbs Total 34500lbs
Steel 9000lbs Total 30000lbs
Dilavar 68lbs Total 21068lbs

I've seen cylinder pressure tests of various turbo/SC engines that are making 3 BHP per CI, and IIRC they are roughly around 2300 psi peak. A very quick peak, but a peak none the less.

If we use that value as a very rough approximation of our turbo engines, that would compare to our typical 3.3L-3.4L putting out around 600 HP at the crank.

Based upon Weissach911's numbers above, looks like we might exceed the total warm clamping force of the Dilavar stud at that HP level? And steel or 17-4PH is the only thing that would hold that pressure level?

[Gunzel]

Guys
It seems plain to me that none of the engineering members have enought real info to produce any actual fact based data. The general conclusion of the thread seems to be that if you spend $1000.00 for 24 studs that cost about $5.00 each to produce you may be OK.
So my question is if you are running an RSR engine, of 3 liter, and putting out approx 325 hp and you use 2 liter steel Porsche stock studs what will happen. What about using 2 liter fiberglass covered Dilavar studs?
Has any normal tight fisted people built high HP engines using stock studs and had no problems. I would assume any Mag case engines would have time certs or something.
Come on non engineering members speak up.



mike

[KTL]

Originally Posted by Gunzel

Guys
It seems plain to me that none of the engineering members have enought real info to produce any actual fact based data. The general conclusion of the thread seems to be that if you spend $1000.00 for 24 studs that cost about $5.00 each to produce you may be OK.
So my question is if you are running an RSR engine, of 3 liter, and putting out approx 325 hp and you use 2 liter steel Porsche stock studs what will happen. What about using 2 liter fiberglass covered Dilavar studs?
Has any normal tight fisted people built high HP engines using stock studs and had no problems. I would assume any Mag case engines would have time certs or something.
Come on non engineering members speak up.



mike

cstreit built a twin plug 10.5:1 compression 3.3L N/A (SC case with 100mm JE pistons and Nickies cyls) race engine with steel studs. No stud-related problems after about 5 yrs on it I believe. It puts out 248 WHP, so that's about 290 HP at the crank.

I'll be using plain 993 steel studs in my 3.2SS race engine build i'm currently working on.

[aws]

I have used the factory steel studs in numerous race/street engines for almost 40 years with no head sealing or case problems, I use 26 lbs of torque--- Ollie's does the inserts on my mag case engines. This list includes (but not all) a very mild street 3.5 w/carbs making 300 rear wheel horsepower, mag case 2.7 making 270, numerous 2.5's making between 260 to 280,and (That I mentioned in a earlier post) a twin turbo 2.5 making 468 to the wheels... none of these engines had head sealing problems and all used factory steel studs because they were available and cheap. I think that Henry's studs would be what I would use if I had to purchase new studs. I would never use dilivar because of the problems I had with the twin turbo 2.5 lifting the heads when I used them and because they break----steel does not break.

aws

[Tippy]

Originally Posted by Henry Schmidt

Here is what you get with Dilavar studs after 65000 miles.
This is a street driven turbo. So much for the constant sealing of Dilavar studs. BTW: no broken studs. The Pistons and cylinders showed little/no wear indicating that this engine was not abused.

You know Henry, I had the same thing happen and just saw this post. Interestingly, mine blew combustion upwards on the intake side. You show an engine blowing it downward on the exhaust side.

Also to your point, my understanding speaking with "chris_seven", is the hotter the engine is, steel will clamp harder on the heads than Dilavar since steel does not expand as much as AL (or Mg).

This is important on boosted engines like mine.

Chris felt the threads in the case should be able to handle the additional forces during this period. We did not discuss Mg cases though.

Beings that your studs go all the way into the hole for extra thread engagement, sounds like it shouldn't be a problem at all. Again though, not sure for Mg?

Now, what that said, mine were under torqued. I had forgotten I was using 993TT studs and used the torque of the factory 3.2 studs.

This led to head lifting and galling of the head to cylinder surfaces.

Not good!!!