The Stage 4 Tuff is one of IAG's strongest and most prepared EJ25 Closed Deck offering. IAG machines the case halves assembled together in our Haas VF-4SS CNC mill to accept the IAG CLOSED Deck Inserts that transform the block into a solid deck. The unique inserts feature small passages that allow needed coolant flow to the deck surface. The case halves are then CNC machined for our new Fire-Lock head gasket solution that is loosely derived from diesel technology where a counterbore step is machined around each cylinder bore allowing specially sized fire rings to drop into the machined area and head gasket bores. The Stage 4 Tuff case is then drilled and tapped to accept 14mm head studs that combined with the IAG Fire-Lock head gasket set greatly reduces head gasket failure during high cylinder pressure scenarios. Next, the short block is Deck Plate bored and honed to 99.75mm in our in-house Sunnen SV-30 the most advanced automotive cylinder hone available. IAG‘s in-house honing process is able to set custom piston to wall clearances to best fit your needs. IAG’s Closed Deck is suitable for street or race use and has been tested in vehicles producing 1000+ horsepower and over 55psi of boost.