The 6 cylinder tach will not read correctly on a four. It will do just fine, however, on a 3 cylinder two stroke, such as an old Saab. Saab 96s with a tach could be either two stroke or V4, and the tachs looked exactly the same on the front and had the same connections but were not interchangeable. I used to like to get the ones from the V4s (great vintage look VDO) and put them in early style 140s. I would remove the ashtray and cut a hole approximately 3 1/2" diameter in its place. Not the ideal location for a tach, but where else are you going to put it. I guess I could have relocated the lighter and other knobs to the right of the instrument cluster and mounted it there.