24.5-25.5cc combustion chamber for use with flat top pistons. This specification of cylinder head is the only modified version for the small-bore based engines Mini Spares supply as it is judged to be the only one worth up-grading to. Based on used core castings, it is modified to current road-sports style to maximise road-sports and track day/weekend-warrior performance when used with road-sports and super-sports camshaft specifications. That means optimised 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.
A surcharge for non-exchange purchase of £300 applies. Heads supplied as exchange units must be in good condition with no cracks, in completely standard form (no modifications), and complete with valves, springs, top caps and collets.
Some companies call this stage 3 but our way of thinking similar to original Special Tuning is as follows-for 998 head
Stage1 gas flowed with std roaad quality valves
Stage2 larger 30.9mm inlet-usually race quality valve
Stage3 larger 30.9mm inlet and 26.4mm exhaust race quality valves
for 1275 head
Stage1 has 33mm inlet 29mm exhaust std valve sizes and gas flowed
Stage2 has 35.6mm x 29mm ex road quality valves and ported to Road Sport spec
Stage3 has 35.7mm x 29mm ex race quality valves to Super Sport/Grand Tourer spec
Stage4 as stage 3 but with either larger inlet or exhasut valves and more modified throat and port work
For real race use ask our technical staff at York or Potters Bar.