998 Cylinder Head 31mm & 26mm for use with Unleaded Fuel

24.5-25.5cc combustion chamber for use with flat top pistons with 30.9mm intake and 26.4mm exhaust race quality valves. This small bore head is modified to current road-sports style to maximize road-sports and track day/weekend-warrior performance when used with road-sports and super-sports camshaft specifications. That means optimized BHP and torque out-put through port shape and dimensions and valve throat shapes developed on airflow bench and dyno/rolling roads to work with the aforementioned camshaft types, along with suitable compression ratios given modern lead-free fuel specifications. High quality Serdi lead-free exhaust seat inserts are fitted. Latest specification manganese-bronze valve guides are used along with the latest specification plasma-nitrided EN214N stainless steel (30.93mm inlet and 26.5mm exhaust) and 180lb (nominal at maximum valve lift) double valve springs to give a cylinder head capable of withstanding a maximum continual peak rpm limit of 7,500rpm and 0.475" actual valve lift. Suitable for auto-testing, hill-climbs and track day use. Combustion chambers are set at 24.5-25.5cc since most engines these will be used for will already be using an elevated compression ratio (CR) through either flat-top pistons and/or larger bore capacities, and their efficiency will boost dynamic CR considerably. 9-stud fitting as standard. This head has the heater take-off port open and a by-pass hose adapter fitted. Both or either can be blanked off as needed.