Engine failures due to defects only happen at very low mileage if the manufacturing process was total crap. Think along the lines of failed to wash the crank or clean side oil galleries before assembly. These engines are very closely monitored during assembly and most things other than loose debris in an oil gallery are caught in the automated inspection stations. This results in a field failure rate that increases over time for engines. Some years ago the best failure rates at lower mileage were well under 1%.

In the US most manufacturers will decline engine warranty if the car is tuned. If you complain to them maybe half will just cover the claim. If you hire an attorney and the failure is not combustion related or structural you will “win” your suit. If it is a piston, bearing, rod, valves or head gasket failure you are unlikely to win in most courts unless you find a reputable expert to prove the manufacturer caused it.

Mildly tuning an autobahn capable car for non-racing use in the US is probably low risk, but we have to accept the risks we choose to take.