t alloy blocks and drew on the experience gained by Nissan with their first alloy block engine, the 1-litre MA series. The technology jump was a large one, although the weight saving of the SR20 block over the CA18/20 iron block was only 9kg. However, as Nissan engineers of the time suggested, “attention was devoted not merely to reduce weight, but to assure functional reliability and to improve NVH [noise, vibration, harshness] characteristics”. The block alloy was heat-treated JIS AC2A, a material already used by Nissan in cylinder heads. A closed-deck design was adopted for these reasons: cylinder head gasket sealability improved NVH characteristics reduced permanent bore distortion To test the reduction in NVH of a closed deck, Nissan engineers had a CA20 block cast in aluminium (the CA being an open deck design) and then tested it back-to-back with a prototype closed-deck SR20. In the closed-deck design the greater stiffness of the water jacket wall reduced radiant noise by 2-3dB over the whole engine rev range. Other Nissan testing showed that cylinder bore distortion of the cast-in iron liners could reach 0.05mm in an open deck design, causing piston slap noise and oil consumption problems. This permanent distortion was reduced to 0.04mm in the closed deck version. A deep skirt block design was adopted to improve powertrain rigidity – but to give reduced NVH, rather than improved engine strength.