I was looking at the Mace cold air intake manifold insulator for the VZ Alloytec V6 and was just wondering of the two types you have which one is a better purchase for power gain? I would say the 20mm manifold?

In regards to power production in the lower RPM range (where they need assistance most, due to their short inlet manifold runners), the 25mmm item would be the better of the two. Otherwise if you tend to visit your engine's rev limit on a consistent basis, then I would go with the 12mm item as it will make more power top end then the 25mm item