[opwieurposiu]

Loss of compression comes from material breakdown, the other big one is from dirt build up. Dirt in the injectors causes bad spray pattern. Dirt in the cooling system reduces heat rejection. Dirt in the lube system increases friction losses. Dirt in the intake and exhaust causes pumping losses.

The amount of dirt a car is exposed to varies by 2-3 orders of magnitude between a farm truck compared to a sports car.

Rarely will you see an old sports car lose more than 20% power. Farm trucks lose 50%+, and the farmers keep running them until they just don't move at all.

*Side note, dirt does sometimes help. As a teen, I had an old ford festiva I shared with my brother. One day we washed the filthy engine bay and after that the thing would not idle. Turns out the dirty grease was plugging a vacuum leak around the pivot on the throttle valve.