Can't think the length that you'd use on a car will cause any issues, of far more importance is the route, ie it is VITAL that it has a DROP POINT in it prior to getting to the map sensor, ad the drop point should be as close as possible to the map sensor, this needs to be around 4" minimum lower point to ensure that any fuel residue doesn't reach the sensor itself, they are very delicate in this repsect a simple wheatstone bridge affair.
tabetha