it depends how you mount the guages. in my 78 280z, just lets talk about the tach, i can use an almost 4inch tach if i have it sitting far back by using the stock black cylinder funnel looking thingy that sits the stock guage farther back or i can run a 5inch tach and still slide it in the tach hole in the dash but it'll sit flush with the dash instead of recessed back in there.