S13 KA24DE feels like having vtec after 5200rpm??

[s13_newbie]

Hi! I have a 91 rps13 w/ stock ka24de.............i dun rev my engine that much, so i dunn when this started........i have noticed that once my rpm reached about 5200rpm, the acceleration rate is faster. for example: <5200rpm, a = 5m/s, >5200rpm, a = 7m/s...........and u can feel the difference, even my friend that doesnt know anything about cars noticed that............any ideas wat went wrong, or any1 had this funny problem b4???? I just has a clutch replaced w/ excedy oe clutch set and a fidenza 11lb flywheel.......and I have a minor leak in the engine - header gasket...............also, i did a complete 5-lug conversion w/ z32 brakes n s14 rims, if that would make any difference........

btw it happens at every gear.........i tried it out on highway



suggestion please......i tried to search, but find nth...........