Shimming main and rod bearings?? Am i crazy?

[Che70velle]

Well...that's a funny subject to talk about among engine builders. Longevity, versus high rpm/power. You can't have both. It's a one or the other deal.
A race engine, for instance, will have an oil pump that will make up for any loss of oil pressure caused by setting up bearings a "little looser". Adding more bearing clearance does free up power, and helps keep oil temps down. Now if I'm selling engines that are supposed to go a couple hundred thousand miles, and I give a crap about my reputation as an engine builder, then I'm gonna set up my bearings to the tight side of spec, because bearings wear over time. If you add boost into the equation, or a high compression naturally aspirated engine, it changes things as well. These type of engines are hard on rod bearings, which is why you often see aluminum rods used in extreme applications. The aluminum rods take a lot of shock from the rod bearings, and crank as well.