Cylinderhead and camshafts

All heads are almost identical, being alloy with whopping ports and with the same size valves fitted across the board. There was a revision in the 2008-on head but it’s minor and relates to the inlet port configuration – although it makes excellent sense for a tuner-base if you have a choice. You won’t necessarily see a massive power increase at lower tune levels but get it up there in horsepower and the gain can be around 10 bhp.These heads are identified with the casting number of RF 3S4G.They began as a US 2.3-litre head but have gradually swept-in, in European engines in general.

All heads breathe extremely well and only need mild tickling for tunes to around the 240 bhp mark — although it’s wise to upgrade the valve springs as these can be notoriously weak. Beyond that and valve sizes are generally increased to around 36.8 mm for engines in excess of 270 bhp.This size plus a touch of porting is generally regarded as sufficient to see 300-315 bhp.

Cams are by mechanical operation and tolerances are extremely high with differences taken up with cam bucket variations. As such, there are no key-ways; the chain-driven cam pulleys rely on torque settings and friction to hold them in place.

Since these engines are more emissions-friendly, they feature low duration and high lift — 257 degrees inlet, with 9.87 mm lift and 252 degrees exhaust with 8.45 mm lift. These are enough for a tad over 200 bhp.

Several tuners again have their ranges of cams — SBD’s and Kent Cams’ examples are similar although the former tends to be slightly more conservative on duration, the effect being that dynamic compression is increased rather than opening for longer and therefore letting more charge in.The net result will be an increase in torque effectively giving you more guts and punch.

A set of SBD CM-DUR01 cams will give you around 215 bhp, coupled with their exhaust and induction, which we’ve detailed over the page. Beyond that, the same company recommend their CM-DUR02 for results of 250-260, while coupled with a CNC-ported head with 36 mm valves, you should see up to 275 bhp. Levels beyond need those larger valves again, coupled with CM-DUR03 or equivalent for peak power over the 300 bhp.