ARP Szpilki do głowicy VW Audi 1.9L & 2.0L TDI PD Engines Drop-In - ZRP-ARP-117-4706 - ARP Head Studs for VW 1.9L & 2.0L TDI PD Engine. This kit does not need any modification, and it's drop-in! For a good reason, virtually every top professional engine builder relies on ARP Pro Series head studs for their all-out competition powerplants. As stated, there's no better stud setup on the market today. ARP uses a premium grade 8740 alloy rated far superior to aircraft quality for openers. Each stud is placed vertically in special racks and precisely heat-treated to 200,000 psi. This procedure ensures complete heat penetration. The results are far superior to those lesser quality studs from other manufacturers who dump pieces in a basket and hope for the best. Each stud is centerless ground following heat treatment, making it as close to perfectly concentric as possible. This procedure involves about ten very slight cuts, resulting in an exceptionally straight part. It's important to note that lesser-quality studs are not even centerless ground. The material is thread rolled in bar stock form (mostly before heat-treat when the material is more accessible to the machine). Because ARP studs are manufactured to such exact tolerances, you will note that gaskets and cylinder heads literally glide into position and are perfectly aligned, something that won't happen with inferior-quality head studs.