OEM Head Bolts & SCG CA625+ 10mm Head Stud Kit VS. Cylinder Bores

There has been alot of talk about the effects of putting aftermarket high strength head studs into the Audi DAZA & DNWA blocks and their effect on the bore geometry. Anytime you replace a factory fastener with an aftermarket fastener you want to confirm if any dimensions have changed. This is a very good practice and well worth the time it takes. Every part will react differently to different fasteners. There is alot to take into account here including the material of both the engine part and the fastener, torque procedure, temperature, and dimensions of the fastener.

What I did here was a simple back to back test to see the effects of our CA625+ 10mm head stud kit on the bore geometry of the block. This test is only relevant to our stud kit. Other stud kits that don’t utilize all threads in the block or are a different diameter than factory can affect the engine block differently. When installing larger head studs and removing block material and/or changing the load location you will likely affect the block differently. Our stock fitment stud kit was designed to utilize all available factory threads and to locate itself at the bottom of the bore.

The Audi DAZA & DNWA blocks are made of a very very strong aluminum alloy and the manufacturing method ensures strength in critical areas. From the SSP:

The Rotacast method is a tilt casting process variation on
gravity die casting. After being filled with liquid aluminum,
the entire die is swivelled through 180°. The uniform
microstructure distribution ensures that optimal strength
is achieved in both the bearing block and top deck areas.
The aluminum alloy AlSi7Mg0.3 is used. The cylinder block
of the 2.5l R5 TFSI engine is the world’s first engine block
to be manufactured using this method.

The OEM head bolts are class 14.9 which specify a 203,000 psi tensile strength and are installed beyond their yield point.

The CA625+ head studs are a proprietary material from ARP and specify a 260,000-280,000 psi tensile strength.

Test Conditions:
70° F
Crankshaft installed with main bolts factory torqued
Low mileage good condition DAZA

Test Tools:
Snap-On 1/2″ Digital Torque Wrench
Deeworks Deck Plate
Starrett 3-4″ Micrometer
Sunnen Dial Bore Gauge

The first chart here shows the bore dimensions. First with no deck plate installed. Then with the deck plate and brand new OEM head bolts. Then with the deck plate and the CA625+ studs torqued to 100 ft lbs. And finally with the deck plate and CA625+ studs torqued to 110 ft lbs. Installation of our CA625+ kit was done using specific installation method outlined in the instructions.

The next chart here shows the change in bore dimensions with the studs at both 100 ft lbs. and 110 ft lbs. vs OEM bolts. The results were only +/- .0001″ which is well within the factory specification and so minor it could simply be from removing and re-installing the deck plate.