Something in the “air flow management” of the engine can’t keep up with the demand as the rpm goes up.
The torque starts falling of fairly quickly before the rpm gets high enough for the math to work out favorably.
In basic terms........ something(or things) is “too small”.
Heads, cam, intake, carb, headers...... or a combination of them.
In a race car, you can often make improvements to that situation by adding more cam duration.
If you do it in a street car, sometimes the trade off for some extra top end HP, in exchange for poorer street manners isn’t what every body wants.
