What year 340 heads got hardened seats?

Mattax said
Except we knew it as American
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Premium, or Super premium. lol. Remember the name change? I think they also promoted as 'white' as part of marketing. My folks used it in our 318 powered Belvidere, along with a slightly advanced timing. Probably helped with 21 mpg they got on long trips to the south. We called it Hi Test too. Don't know if that was also what the company's called it, or just slang.

Yup I remember American and I used to get those green dinosaurs from Sunoco too! Dang necks broke off fast in the tub! I think it was life boy but my mom used another brand once when she washed my mouth out. I used to hear this as a kid > filler er up with ethel lol