Blackstone Group, the world’s biggest private equity fund, will be investing $65 million in Hyderabad-based engineering firm MTAR Technologies to pick up 25 per cent stake. The funding will be made in a mix of primary and secondary equity after getting necessary regulatory approvals, a company statement said here. MTAR is a leading player in precision engineering. It makes machined parts for nuclear power reactors and engine components for aerospace and defence applications. “Blackstone will acquire a significant stake in MTAR, which will come to around 25 per cent,” sources close to the deal said.