An episode of engine masters proved that 1.5 stamped steel and 1.5 roller rockers had identical numbers, but 1.6 RR improved their test engine by 15hp / 6ftlbs. But their test engine was heavily modded and rev’d up to 7k. I think 1.6 might squeak another 5hp and maybe 5ftlbs. I don’t want to do any restrictors so we’ll see.