The process involves chemical cleaning, a full strip down of the head, pressure test, full decoke, the head is then fully ported, valves polished, new 3 angle valve seats then fully reassembled and quality checked.All modifications used in production of the cylinder heads supplied by GT Turbo Spares have been flow tested. These results show an improved air flow will be achieved with most camshafts (Inc standard camshafts). Please email for more details!£50 will be refunded upon receipt of a fully functional / usable cylinder head (inc valves, springs and collets).Suitable for both the Phase I & II Renault 5 GT Turbo.