Is it recommended to use a 12mm manifold insulator with a 25mm plenum spacer in an Ecotec 3.8L engine for boosted applications?

Yes, we recommend pairing a 12mm manifold insulator with a 25mm plenum spacer mainly for packaging reasons, as this combination typically clears the bonnet without modification. Ideally, the best setup would be a 25mm manifold insulator and a 25mm plenum spacer for maximum gains. However, this would generally require reworking the bonnet reinforcement to provide adequate clearance.