CST 3030 40 & 60 Pistons  

CST3030-40 & 60 PISTONS 

Manufactured by the same company that has produced the excellent 998 flat top pistons and now also the 1098 flat top pistons using the same, super-grade, extra-high silicone content material specifications, these pistons have an optimised crown and dish (6.0cc) shape for improved squish/burn. The piston is lighter than most cast pistons of this size and a lighter wrist pin is used to enhance this. The wrist pin is also supplied oil from the oil control ring land rather than relying on 'splash' from whirling components. 
The piston ring groove design has stepped away from convention, utilising specs distilled out of intensive testing and are as used on the very latest high-performance pistons for mega-powered Japanese engines. One feature of this design is that the rings do not retract fully into the groove – this is NOT a design fault! 
Ideally, the top and second compression piston rings should be gapped to give 0.004” per 1.0” of bore diameter. Some ring sets come supplied with larger ring gaps, up to 0.020”. This is not a problem. The manufacturers tired of complaints for customers who damaged their engines because they didn't bother setting the ring gaps correctly. To avoid this completely they decided to increase the rings gaps. Industry leaders tests have shown that gaps in the order of up to 0.025” make no difference to performance. On engines I have dynoed with such ring gaps, post dyno compression tests and leak down tests (checked on all dynoed engines as a matter of course) showed excellent readings in both cases. The oil control rings should just be assembled to the piston as they are because the assembly is designed to work at it's compressed in-situ form. This is not measurable with the piston out of the bore. 
The higher silicone content and advance heat treatments used also creates a more stable piston which dramatically reduces expansion under combustion/running conditions. Consequently lower piston to bore clearances are required. These pistons are manufactured for race use so will give correct piston to bore clearance on the relevant bore size. Suggested finished honed bore to piston clearances are as follows - 
Road/fast road - 0.0015” to 0.0017” (0.0381mm to 0.0432mm) 
Sports/super sports - 0.0018” to 0 0.002” (0.0457mm to 0.0508mm) 
Race - 0.0022” to 0.0025” (0.0559mm to 0.0635mm) 
Turbo road - 0.002” to 0.0025” (0.0508mm to 0.0635mm) 
It is feasible to enlarge the dish for extra capacity if required. Use the centre depth of the dish as the start point. Using a radius tipped tool similar to the radius in the dish corner as is, increase the depth of the dish by 0.082”/2.08mm (dish is then 0.200”/5.08mm deep) then machine the dish wall out towards the crown edge. To within around 6.5mm of the crown edge will give a dis of approximately 10cc, out to within 5mm a capacity of approximately 12cc. 
NOTE - The piston rings are position/orientation specific: 
The top ring is a moly-faced/shiny silver type that is non-directional. 
The second ring fits with the markings uppermost 
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