We have spent many years perfecting the work on our heads. We have flow tested heads from Intense, Thrasher, RAT, and many private shops. When we got close to our final design we had two shops do flow testing on the same ports to verify accuracy. Once the port design was final, we supplied the shop of our choice with over a dozen valves to test, modify, and destroy if needed.
ZZP has created what we believe to be the best design on the market. We have done this by playing with the back cut depth and angle, valve size, and transition shape from the stem to the head. Naturally aspirated cars require high port velocity.
Using the latest technology from Fastbikes that is used on 14,000 rpm motorcycle heads, we have been able to make large gains in NA applications by keeping port velocity high and increasing compression by milling the heads.
Every stage of our heads use the same size and cut of valves. They are cut from special blanks and we can make them to any requested size. We tested valves as large as 1.96 but have found optimum to be 1.89 intake and mid to upper 1.5x exhaust. We chose 1.55 for exhaust because the seats last longer. Our heads will last up to 100k miles depending on the spring pressures used. This is done by keeping the factory hardened seats in tact as much as possible. Our custom valves are approximately .100 longer than stock to correct valvetrain geometry. This way we are splitting the difference as you add lift to the factory setup. Instead of just pushing the rocker lower, we start the rocker .100 higher so assuming you add .200 lift to your factory setup you’ll keep stock geometry. Please be aware of this when installing our heads. This along with pushrods length, head gasket thickness, block decking, rocker arms, and head milling play a factor in setting up your geometry.
Email or phone us if you need help with any of this so we can assist you in getting your engine perfect.
Hollow valves reduce reciprocating mass, are easier on the seats and increase RPM capability of the heads. Lighter spring pressures are easier on valve train, create less rocker deflection, and will keep components lasting longer. Higher spring pressures will increase rpm capability of the heads and allow more aggressive ramp rates. Our 90# springs are good to .550 lift, 105 and 130 Comp springs are good to .600 lift. For racing applications, we have a dual spring 135# seat option available rated to .650 lift. We can shim springs up or down to alter spring pressure up to 10 pounds. This can be useful in custom tailoring spring pressures to match cam specs.