All Berg heads are new genuine VW complete, have hard chromed valve stems, stellite exhaust valves, hardened seats and can be used on engines using unleaded gas. Modifications in USA by Gene Berg Enterprises.
Head cc values listed for the heads are approximate. Remember, the stock 1600cc VW has 7.3:1 and that requires at least 91 "leaded" octane gas. Larger bores increase the CR and require Semi-Hemi cut and spacers under the cylinders. Any CR higher than 6.6:1 with stock chamber or 6.9:1 with Semi-Hemi cut heads (on carbureted engines) will require special fuels that are manufactured to support higher CR. These fuels are called racing fuels such as those sold by VP Racing Fuels, CAM2; Union 76 race fuels, and Phillips. For maximum life you must follow the CR vs. octane formula in GB 801-CR.
Please note: Semi-Hemi cut heads are not required on fuel injected engines that run at sea level. The computer corrects the fuel curve to protect the engine. It can be used for altitude.
When you run our Semi-Hemi cut heads you must run at least 4 or 5 degrees more timing than normal and possibly one main jet smaller. This is due to the flame traveling farther and burning completely to the edge of the cylinder. Not advancing enough will likely make the engine feel weak or slow to respond and run too rich as you are not getting a complete burn before the piston moves away from the chamber. In other words, the fire is not being completed where it makes the most power. Also, see Berg instructions for GB 622 distributor in our Book of Instructions.