E-street vs Promaxx vs 440 Source

On your half, that’s fine.
Ive never had a manufacturer give me a rpm range to there heads, never seen it advertised. IMO, it’s a load of ****.

Any given engine can have to much head or not enough cylinder head for what ever size the engine is. On just a cylinder head, rpm is part port window size and part valve spring for valve control that would point to a rpm range.

I’m floored you were told that.