The valve springs ratio needs to be set up correctly when assembling the head work with the set load variations on each valve spring. This is standard procedure when building a race engine which will be used for constant high RPM and requires smooth reliable operation. The real way of accurately measuring and setting each valve spring for each cylinder head is very time consuming and with very high costs involved to eliminate any unwanted values which can cause harm to the head system. So we made this in-expensive and time saving product to aid you achieve the accuracy required for your race engine or precision street engine. All TOMEI complete engines use these valve spring sheets for the final adjustment settings and have been proven to be a reliable and worthy product.