TUNING THE K-SERIES ENGINE
Many fail to appreciate how much can be gained from even simple cylinder head modifications. The twin-cam, 16-valve configuration is certainly far more effective than overhead 8-valve pushrod designs but they still suffer from volume production shortcomings that allow careful mods to deliver significant power gains. What’s more, these usually see standard engine management systems easily self-adjust so no added mapping changes are needed. Although, with more comprehensive head mods, mapping changes will add more power across the whole rev range.
16-valve MPi heads are common to K-series 1.1 to 1.8-litre engine capacities meaning that the valve sizes are relatively large for a 1.1 engine, balanced for a 1.4 (for which they were originally configured) but progressively slightly small on a 1.6 or 1.8 engine. (Note: not all 1995-on MPi heads are quite the same as, up to 1998, they used a manual tensioner and, from 1999, they used an auto tensioner with different belts. Later heads can be converted to the earlier belt spec., but not vice-versa).
MPi head retaining standard valves
Having travelled the modified head route many times, with similar results, I can give a reasonable expectation of what similar changes should deliver. The first modified spec. of head uses a carefully cleaned up standard head, meaning no deep grinding to change port shapes, retaining standard valve sizes, seats with three angles: 30-, 45- and 60-degree cuts etc. This is the most cost-effective first step that could also incorporate reconditioning aspects, such as new guides and re-cut seats, but keeping head skimming just enough to ensure that the surface is completely flat as there isn’t much material available to skim. My colleague Peter Burgess does my work in this area and he describes this spec. as Econotune.
One example was a 1998 MGF with a standard engine apart from an ITG Maxogen AB65 induction system. These head mods saw the engine deliver an extra 22%
