Car engines are generally unsuitable for aviation applications, as they bear much lighter loads than airplane engines and are designed aproppriatelly. Average (European) car engine runs on 25-35% of full power, American even lower, airplane engines run on 60 - 75% of rated power most of the time, definitelly not below 55%. Plus you need to figure out the thrust bearing issue, which car engines do not have.
All in all, I would not risk more than suggested 500$.