I have used Lucas Upper Cylinder Lubricant for years in other vehicles at a 50-75% dosage. Am using it in HIPPO but I haven't come to any conclusions due to large variations in seasonal temperature combined with the fact it uses so little fuel. I haven't experienced anything untoward so far. Fuel efficiency was about 6.7 litres/100km in the summer and is about 7.8 litres /100km now in the middle of winter with winter tires. 75% highway 25% city. Typically Lucas gives me about a 4-6% bump up. Not sure how well the Atkinson cycle can benefit from it.