The Hyundai was badly damaged, while the Mazda was burned out.
The arsons followed similar incidents last weekend, when two cars were set on fire and another interfered with early on February 25.
Those cars were a blue VW golf parked in Palm Avenue, which was badly damaged by fire about 3.30am, and a blue Mitsubishi Galant set alight in Imperial Terrace about 6am.
As well, a vehicle in Rodrigo Road had the handbrake released during the night.
"Police want to hear from anyone in the Kilbirnie area who has witnessed any of this suspicious activity in recent times or who has any information on any of these arsons over the past two weekends," Mr Mercer said.
"It's also a timely reminder to ensure car windows and doors are secured when not in use, whether they are parked in driveways or on the roadway. It's also important that no valuables are left in cars."