Charge Motion
The flow bench is one tool of many very important tools used in this industry. A raw airflow number on paper however, does not tell the whole story. We have to remember that the majority of heads and manifolds do not flow air only, but have to process a homogenized mixture of fuel as well. Recent developments have made wet flow technology a reality for the modern day race engine builder/cylinder head porter. Basic physics explains quite clearly that there are substantial differences between gas and fluid flow. The dissimilar masses of this 2 part mixture will cause the two different elements to move throughout a port differently. The heavier mass of the fuel can not make the turns air alone can, and the fuel will literally seperate itself from the rest of the mixture stream, ending up on port and combustion chamber walls as droplets.
Match a very shallow valve angle with a very low port floor height and you have created a flow disaster...AKA..the Ford 2.3l factory heads. These heads feature a casting limited poor bowl approach angle which leaves for a very difficult short turn radius to work with. The transition from port floor to valve seat is very abrupt, and in most cases causes air to shear across the back of the valve. If the air is not able to make the turn at higher port velocities, you can imagine what the fuel is trying to do in a dynamic state on the running engine. The minimal wet flow work I have done on factory 2.3l castings showed a complete disaster. I found fuel was slamming against the long side of the bowl, and once it made it past that it slammed against the back cylinder wall. Very little mixture was making it down the bore where it belonged. With the information I gathered I adjusted the port shape, chamber shape, short turn shape, and combination of valve seat angles to help get the fuel down the bore as a mixture, not droplets. I feel the slight reduction in mid and low lift flow was well worth the wet flow improvements that could be had. Whenever the head is pulled from my own test engines, I am always inspecting the port walls for stains left from the race fuel, which indicate how the fuel is moving in the port. I also carefully study burn patterns in the combustion chambers and try to change something every time the head goes back on the engine for the next dyno session.
Testing on aftermarket 2.3L Esslinger heads with a far better port approach angle to the valve thanks to the nicely raised port showed far better wet flow characteristics than modified factory iron castings. The way I see it should reduce BSFC, ignition lead, and provide a more volitile burn ultimately making more power. Wet flow is an area I hope to continue to further develop in the future with the aid of more thorough dyno testing and the adaptation of a wet permanent wet flow system to my bench.
| 
