I too am chasing one! I think the inlet pipe diameter is the same as a 2G elbow but the interior sizing is better especially as it doesn't taper down to the 2G's 55mm and matches the VR-4's 60mm throttle body. I ended up using a die grinder to improve the 2G elbow but I feel it is a bit thin in places and an HKS one would be far better (and period correct!)