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The Astra H VXR engine (Z20LEH) is a development of the Astra G’s Z20LET power unit. Rather than simply diving straight in with remaps, we stripped an engine down to component form to examine its internals and get a real feel for what has been done. One of the main differences is the block has been equipped with oil spray jets. These jets cool the pistons by spraying oil at the underside of the piston. These oil spray jets were added for manufacturer's durability reasons because the LEH engine produces 240PS as standard (where the LET engine only produced 200PS), and not because, contrary to internet myth, the factory Z20LEH engine runs lean. In fact the Z20LEL and Z20LER engines used in Astra H run at the same target lambda value from the factory as the Z20LEH engine, and the LEL/LER engines do not have under piston cooling.
The pistons themselves are high yield forged items with the skirts Teflon coated to reduce noise and wear. Gone are the Z20LET’s counter rotating balancer shafts. This sharpens response whilst helping the engine rev much more quickly. At the top end the inlet manifold is revised however this revision is across the whole of the MK5 engine range, the VXR though getting new larger injectors. The turbo charger is a hybrid item, equipped with a better A/R ratio and stronger bearings. The manifold it has been built into is cast in a higher yield of material making it less prone to cracking. This turbo unit has been available for a while now from Vauxhall and we have already used many times on the Astra G and the VX220 with good results.
Once we had established the above we then under took mapping our first VXR. The results are very good, however we could not take the car any further than this on the standard intercooler. So extensive cooling modifications were investigated and developed for the next level of power, to ensure the longevity of the engine and surrounding components.