Porting and gas flowing engine heads.

"Your first PORT of call."

Porting an engine
The inlet and outlet ports on the engine block are usually larger than those of the manifolds that connect to them to help cope with mismatched alignment. Most are far from smooth due to the casting process so small gains are there to be had by smoothing out and polishing the insides. Engines need to breath as freely as possible and obstructions cause turbulence and this is not very good for airflow. The air intake port would not benefit by opening up to match the intake manifold so most port matching work is best performed on the exhaust ports.

A word of caution though if you enlarge the exhaust port fully to the size of the gasket when the manifold port opening is smaller than the gasket you will completely mess up the airflow and will lose power - the aim here should be to get the two port openings to roughly the same size. Torquecars members have done a satifactory job on their heads but a specialist really has so much more to offer. Really, as far as a DIY approach goes, do little more with the ports and manifolds than a smoothing up and polishing (the intake manifold has the job of assisting with vapourising the fuel and benefits from a pitted rough surface so please do not polish the intake manifold!).

Air flows in a similar way to water, the faster the air moves the more gloopy and sticky it behaves. If you have ever hit the surface of water at speed you will realise that it is not soft and liquid! The aim in the head is to get as much air and fuel mixed as effectively as possible into the combustion chamber. The most important area within the engine, as far as air flow is concerned, is the valve seats and bigger power gains can be has here especially for engines with slightly higher lift valves with some careful blending below the valve seat insert to remove the steps and grooves.

Putting the gasket over the ports will show how much needs to be taken off for a good airflow match. Use some nail varnish to mark the area then remove the gasket and start cutting away with a grinding wheel in slow, long deliberate arc movements.

The angles on the seats is also of concern to the engine tuner. Generally speaking, the thinner the seat, the more unreliable the engine will be so we are back to the eternal compromise of power vs reliability. Because each engine type is different with some producing more heat than others and a wide variety of 20v 16v and 8v systems you are better off leaving head work to the professionals who are able to measure the airflow through the head and help create the perfect head setup for you.

Each type of engine is better suited to a specific valve seat shape just as your driver requirements will create a different range of properties that the head machinist has to work to. Fitting larger valves will generally improve the airflow through the head of the engine into the combustion chambers and will help the engine cope with a much higher state of tune. Adding longer valve stems will also release a little more power too in many engines although you really need to avoid the possibility of a valve hitting the piston!

Caution – if the airflow is too free then the engine will effectively lose it’s torque and can be totally un-drivable below 2000 revs.