The E-Tec 170 heads feature 170cc Vortec-shaped intake and 70cc exhaust ports. They flow 20% more on the exhaust side than the cast iron Vortec heads and produce power up to 6000 rpm. The 64cc combustion chamber will result in approximately 9.5:1 compression when used with stock pistons in 350-inch engines. E-Tec 170 heads come with 1.94" intake and 1.55" exhaust valves. 50-state street legal.