hmmmm.... the turbo head uses sodium filled valves, so you have that to ponder.... My understanding is that the turbo and non turbo head use the same cc's, the major difference is piston and maybe head/deck height (but don't think so cuz the belt app is the same turbo to non...... I'm guessing that if they used the stock gasket, you are prolly at the same comp ratio as the stock turbo... Scott