There is no difference between the mass air motors and the speed density ones. If you want to convert you car to mass air, which is highly recommended, you will need the mass air computer, mass air sensor, intake pipe and filter. There is the A9L computer which is for manual transmission cars and A9P for auto's. Iv heard it doesnt matter which one you get and iv also heard it does. I did the swap on my 87 5 speed with the A9L with no problems and my cousin did his 86 5 speed with the A9P with no problems.