The real question is why Lycoming cost $80k vs $10k for V8.
If you mean a Lycoming aircraft engine vs a car engine the answer is quite simply mass production over millions of units vs limited production over a few thousand. Then spreading the cost of development, production and liability both for faults and continued support over those numbers. You order a part for a piper or such it's effectively made for that order, or comes from limited spares stock. You order a part for your car it's shipped from a stock of mass produced parts, it's amazing how expensive or just outright impossible to get certain parts for out of production cars where you have to start fabricating your own stuff.
Most importantly would you be able to operate a commercial passenger flight with a car engine, most likely not.
Is the V8 or Lycoming the more reliable for aircraft use, who really knows, but one is certified and the other is only certified for glider towing.