Studs for 1974 mag case
 

I’m doing a complete rebuild and upgrade of my 74 2.7 CIS engine. Putting in high comp Wossner pistons, hot street cams, carbs, etc. I know the issue of studs for mag cases has been discussed here many times before, but since there seems to be many different rcommendations I thought I’d ask again. Putting in Case Savers seems to be a given, but what studs should be used, especially given that the engine spec will be bordering on a racing one? Are standard steel ones, in combination with the case savers, fine, or should I go for 993 Dilavars? Or Race Ware?

Thanks!

cyl studs
 

I have used ARP, 993 dilivar,raceware,early steel studs, Supertec studs and depending on what the application and availability. My choice for high performance and race engines is the Supertec set from Henry
Mike Bruns

It's my understanding the best studs made were those that came in, strangely, the mag cases. I've always replaced them as a precaution but have also been told those studs are fine to use, although I never have. Someone else care to chime in?

Steel studs work just fine, BUT,....BUT, engine oil temps must be strictly controlled (this applies to all mag cases) for durability. Keep those engine temps below 200 deg F and you'll never have any problems with the studs/case again.

Also bear in mind that the 'stiffness' of the stud will significantly influence the force generated by expansion for a material with a given Coefficient of Expansion.

Studs with the largest shank diameter will generate the highest force and this force will be directly proportional to cross-sectional area of the stud's shank diameter.

Dilavar, clearly has a relatively high coefficient of expansion and is the most effective means of controlling the thermally induced force.

The majority of other studs all have a similar CoE and Young's Modulus so the studs with the smallest shank diameters are the least likely to pull out.

Thanks everyone for chiming in! Given the price for steel studs, I will probably go for those if they work just as well as the more expensive options.

Carl

What if your engine runs hotter than 200? Would fex Supertec be a better option in that case? It currently runs below 200 for street driving, but that might not be the case on the track.

Thanks!

IMHO, you need to get those temps under control and thats the key to durability, reliability, and longevity with any mag-cased engine.

I would suggest reviewing your oil cooler system and its ducting to find the necessary improvements you need.

Thanks Steve. Understood. I do have an as large Setrab front mounted oil cooler as I can fit, so hopefully I should be ok.

Excellent.

Just make sure that the air flowing through the cooler has an unobstructed path out of the cooler. :) :)

Standard steel, Supertec, ARP and Raceware studs all have a CoE of approximately 11 ppm per degK.

They all have a Young's Modulus of about 200GPa.

This means that for a given temperature the Thermally Induced force created by expansion will be a function of the shank diameter of the stud as the metallurgical differences will be insignificant.

A standard steel stud has a shank diameter of 7.7mm, hence an area of 46.6mm^2.

If we increase the shank diameter to 9.6mm the area becomes 72.4mm^2 which will result in a 55% increase in the pull out force due to expansion.

This would be equivalent to running the engine at over 300 degrees.

The long term effect of increasing the stresses created by expansion will make the case material more susceptible to a phenomenon known as stress relaxation.

This may not be an issue for very low mileage engines but in the limit increasing the stress on Magnesium cases is something I would try to avoid unless it was absolutely necessary.

If you don't want to use Dilavar then I would used a standard Porsche stud. 901.

It has a small shank diameter and is well made and has a better 'thread fit' than any aftermarket stud we have checked.

I read just read this post from you in another thread from a few years back: "We have recently been manufacturing Titanium Studs for this application using a 6AL4VELI alloy which has been aged to 170ksi tensile strength. We have fitted around 10 engines with these studs but so far only have around 8 months of use. They are much more cost effective than Dilavar."

Did you have success with those? If so, could be an option.

We have fitted around 20 engines with these studs and have no reported issues.

We only have enough studs for our own use at present although we are planning to make more.

The lower Young's Modulus of Titanium means that the force due to expansion is around 50% of a steel with a similar shank diameter.

Ok, glad to hear it. Do let me know if you change your mind regarding selling a set as it sounds like a good option for my build.

I did the research on this a while ago.

No Dilivar. Steel is fine. Supertec if you want to spend a bit more.

Chris