after installing a dc 4-1 ceramic coated header (designed for a 94 LS, i was told it would fit any b series block) i brought the car to a local muffler shop and had custom 2 1/4 " piping with a trust muffler installed. now the engine vibrates annoyingly at 1.5k rpm, above and below 1500 rpm the car is fine. but at 1500 rpm it vibrates and rattles everything in the car and makes daily driving almost unbearable. anyone know whats going on? thanks
seems like you need a resonator installed to reduce unwanted frequencies within the exhaust system that is creating vibrations.
was one installed? also check your heat shields under there and make sure everything is tight.
i forgot to mention i had an 18 inch resonator installed also
and i had the heat shield problem before and its not the problem, the vibration is coming from the motor.
check your motor mounts.
Originally posted by spikeymike
check your motor mounts.
thats what i was thinking…
turns out it is the drivers side motor mount, my mechanic told me it was messed up after he reused it for the b18b swap! 
o well he said he’d put in the new one for me if i brought the part. where could i find a drivers side motor mount for cheap?
wow, after changing my clutch back to the used stock one, i’ve had the same problem except at 2400RPMS, where the shifter just vibrates and goes nuts. I had a messed up drivers side mount, but then replaced it and it didn’t go away… any thoughts?