The constant need to improve the manufacture of products, industries have introduced into their production lines several existing concepts to provide total quality in their designs, ensuring that their products are within specification and that all have the same functional outcome. In the manufacture of engines is the same trend. They need reliable processes in the design, seeking repeatability of results, where the engine vehicle has great influence and these large sources of emissions. Thus, it is very important to improve the functioning of the engines, in order to reduce emissions. Furthermore, it is necessary to make functional improvements, meeting the demands made by the market, reducing power losses and fuel consumption.One way to increase the functional efficiency of the engine is to improve the airflow into the engine intake. This could, as a result of reduced fuel consumption, increased power, lower temperatures and pressures inside the engine, reducing wear of components, increasing of the life cycle, reduction of emission levels and improvements in driving the vehicle, especially at startup the vehicle. But even with a good design, it is necessary to know the consequences when occur in the manufacturing process dispersions, knowing also how the product is susceptible to possible manufacturing faults.In the production of cylinder-heads there are several critical points that can generate faults positioning of the work piece during the machining process. To reduce these failures was built an attachment part in the operation of machining the first hole. Even with this device, some parts are still out of dimensional specification.The great interest of this work is known, through assessments dimensional, functional testing flow bench and dynamometer (performance at full load and emissions tests), if there is any influence caused by the dispersion of the machining of the guide holes the cylinder-head of an engine and quantify this difference.Thus, we made three groups of four cylinder-heads where all the first group has its dimensions within specification, chosen as standard, the second group has a quota of positioning hole inlet valve 1.5 mm outside the specified left and third group has the same dimension 1.5 mm outside the specified right. All cylinder-heads were tested on the same set engine-dynamometer and with the same instrumentation, to increase the reliability of results.After performing tests, the results showed a variation of 4% in the average number of swirl in the cylinder-heads changed from the standard group. It was also shown that the influence caused by the dimensional dispersions did not affect significantly the performance and emission level of the engine.