CYLINDER HEAD Best cylinder head Price: Haggle Where: Breaker's yard Vauxhall has tweaked the cylinder head design several times over the past 13 years. The early C16XE head (casting number: 90472726) is a cracker as it uses much larger ports, whereas the later X14XE and X16XE use smaller and different shaped ports that peg the power back. The very latest head casting (number: 90400187) uses triangular inlet ports, which work a lot better, gaining up to 12bp. Gas-flowed cylinder head Where: www.sbdev.co.uk The standard cylinder head is very efficient and will flow up to 180bhp on 1600 and 150bhp on a 1400 before headwork is required. Beyond the point SB Developments can supply a flowed item with heavily modified exhaust ports (they weld them up then re-machine them to alter the shape), new valves and guides to gain up to 20bhp.