Most smaller screens used in a CarPC setup runs on 800×480 resolution. To force Raspberry Pi to output 800×480 resolution via HDMI, add the following code to /boot/config.txt with a sudo nano /boot/config.txt command. Remember to remove previous parameters if they exists already.
hdmi_cvt 800 480 60 6 0 0 0
After a reboot, you should be able to get your Pi to display crisp and clear 800×480 native resolution on your screen.