Porsche ARP 204-4206 Custom Age 625 Porsche 911 Head Stud Kit Inc. Nuts & Washers 204-4206
Porsche ARP's Custom Age 625 Porsche 911 Head Stud Kit fits all air-cooled Porsche 911 engines from 1965 through 1998 and 2.0 through 3.8 911 including 930, 964, and 993 models.
ARP's head studs are proven and tested for a lifetime of reliability and performance and are required for use with Nickies cylinders. (ARP or equivalent upgraded head studs can be used where OE head studs are not compatible or recommended). ARP Pro Series cylinder head studs are cold-forged to ensure molecular integrity. They're heat-treated prior to thread rolling and machining. ARP Pro Series include 12-point nuts and hardened parallel washers for an even load distribution and accurate torque readings.
The reason for offering replacement studs stems from the fact that our testing found that no available head stud was compatible with our Nickies or any aluminum cylinders for that matter, with exception of the 911 models equipped with aluminum cylinders from the factory. In most cases, the factory head studs are unable to perform satisfactorily under the increased expansion of an aluminum cylinder, in most cases leading to head leaks and fastener fatigue.
On 911 models, certain engines came fitted with Dilivar head studs, which were designed to match the expansion of the cylinders, but also suffered from hydrogen embrittlement, which is a condition that results from the accumulation of hydrogen gas in the atomic structure of the metal. This gas flows to the point of high stress (stress risers) and causes microscopic cracks. The hydrogen then flows to the “new” crack tip and causes it to crack further. In this way the crack moves across the part, because the crack-tip IS the stress riser. Finally the crack gets so large that the section is not large enough to support the load. Hydrogen embrittlement can take place without tensile stress. ARP® employs a baking process that purges hydrogen gas from the steel, eliminating this problem.
Alt. Number: | 204-4206 2044206 |
Brand: | ARP |
Model: | 911 |
WH Rack: | N10-1 |