Efficient high-flow cylinders heads make big power. High quality castings made from high-nickle iron or quality ingot aluminum stock make reliable heads that do not easily warp or crack with heat and/or pull apart with high valve spring pressures. I am not sure if more people have been taken by cheap overseas head castings that look like something out of the box or by slick politicians promising free lunches, either way, too many. The ZL1 Speed Shop REFUSES to sell head castings that do not live and perform once installed on a running engine. We have seen far too many engines destroyed by these junk castings peddled under many different names whether machined overseas or in the USA. Some shops claim they can be made better and/or can be made reliable with machining or better hardware or other modifications. Our response: RUN, do not do it! We use only trust worthy castings capable of 2hp per cfm intake air flow that can handle high valve spring pressures and heat with out failing. We have been custom building, testing, and porting cylinder heads for decades, along with pairing the right heads with our custom grind camshafts in head and cam kits. We know how to blueprint heads correctly so that open and closed spring pressures and coil bind are correct for the cam that will be used and safe for other valve train components that will be used. We know the correct head hardware to be used depending on application and intended use whether it be inconel exhaust valves for heavy boost and/or heavy nitrous applications, light weight valves for high RPM operation with lighter valve spring pressures, and how to set up heads in a way to reduce spring serge that is seen at high RPM with spin-tron testing. Contact the ZL1 Speed Shop to discuss your cylinder head and valve train needs. We offer small block heads flowing to 420cfm and big block heads flowing to 600cfm! Heads are sold as singles, on the site, select two as a pair at checkout, if two are needed.