old rumor about synthetic oils and flat tappets - fyi nascar engines still use flat tappets and use full synthetic oils (granted they add more ZDDP due to thier high rpm high temp environment)Did you have the engine built for you? If so, ask the builder. They should have an opinion. Mine recommended Rotella 15w40 but said any multi viscosity would work. He did specifically say that synthetic oils, in his opinion, were not designed to work with flat tappet engines.
This question is bound to create many responses.
40W?? Are you sure??
Paul in CT
My grandfather always ran 10W-30. I've tried ND30, HD30 and am currently using Rotella 15W-40 since the higher amount of zinc should be nicer on the tappets. Whether this is true or not on a low stress engine like the A is subject to debate.
Bottom line, any oil designed for modern cars, synthetic or dino-juice, should be fine assuming it's in the right viscosity range, probably 30-40 weight for summer driving.
Non detergent oil is for engines without oil filtration.
Clean rebuilt motor. What's the recommended oil? Pennsylvania summer driving.