I have changed my stock crank pulley and the 2 cam gears to lightweight ones.

Nice!! Car does feels better.

However, there is a vibration felt when I step a little more gas at say... 2500rpm, I can feel the car vibrate before it change to the next gear at say... 3000rpm. The vibration seems to be coming from the lower front of the firewall. (just in case... my car is a right hand drive).

Any idea why?