When Chevrolet/Lotus designed the first series of 32 valve LT5/ZR-1 engine piston/liner assemblies (1990-1992), the rings were designed to seat with normal oil in the engine. Even at that, the rings in those LT5/ZR-1 engines did not fully seat until about 15,000 miles. The factory oil fill at the time was Mobile 1 synthetic for the regular Corvettes and regular oil for the the ZR-1 cars. GM advised owners not to use synthetic oil in those ZR-1 model years until that mileage was reached. Ostensibly, earlier use of the synthetic oil might actually have prevented proper seating of the rings for a long long time. In 1993-1995, GM used the standard factory fill of Mobile 1 oil in both the standard and ZR-1 Corvettes. The LT5/ZR-1 piston ring material and design were changed in 1993 (along with a slight redesign of the piston itself) to allow seating of the rings using the synthetic oil right from the onset. The ZR-1 engine used Mahle factory assembled piston and liner assemblies. The units were computer/machine assembled to tolerances of .0001 of an inch in only two available sizes, which were matched in each engine assembly (Size A and B). The liners were forged aluminum Nikasil-coated with life expectancy exceeding 300,000 miles. The Nikasil coating used in the liners was a similar design used by Porsche and a number of exotics at the time. Those Corvette assemblies retail for over $500.00 each, and re-Nikasiling the liners typically runs in excess of $150.00 per cylinder liner. The Nikasil lining was very durable, and the rings were designed to wear in to the lining, not vice versa or in tandem. So, the bottom line is unless the ring material is designed to seat properly (and seal) with synthetic oil and the proper cylinder lining material, it could take a long time for the motor to "break in". Also, GM used forged aluminum liners because the LT5/ZR-1 engine was a wet sleeve motor, and disimilar metal issues could have arisen if cast iron was utilized as a liner material. I'm not sure what our GT engine cylinder liners are, and if the engine is classified as wet or dry sleeve. Perhaps someone familiar could provide more information.
