Pennzoil vs. Mobil 1: both are full synthetic API SP oils at similar prices. The real differences come down to base oil source and certification coverage.
Mobil 1 vs. Castrol Edge: same base stock, same price. The real difference is OEM certifications — dexos1 for GM, BMW Longlife for Castrol.
The best oil for turbocharged engines is full synthetic API SP — brand and viscosity matter too. Here's what turbos need and which oils deliver it.
AMSOIL Signature Series costs roughly twice what Mobil 1 does. Here's what you actually get for the premium, and whether it changes for your engine.