The centermount fan housing is popular because it allows more carb access space between the housing and the carb, and it looks purposeful, it's shape related to the original Type 547 blower on the 1950's era Porsche Spyders.
We began this fan housing project a couple of years ago, in hope of making the "centermount fan housing" cool more efficiently. According to the ad claims on the websites that sell them, the absolutely hollow (no baffels or vanes) housings distribute equal air flow.
But they don't. One of our staff is a retired NASA-project engineer who specialized in flow dynamics, liquid and gaseous. He dismissed the equal air flow claim with no more than a short physical inspection. Facing the engine from the rear of the car, the fan turns to the right and the blades direct forced airflow to the right and up.
That means cylinders 1 and 2 get plenty of air, but on the cylinders 3 and 4 side there is a storm of turbulance as the forced air strikes the inside top of the fan and is forced downwards against what air manages to swirl around clockwise with the fan and tries to escape to the left. In short, the centermount housing, as sold, would produce less efficient cooling than a 36hp housing and significantly less than a doghouse type.
We saw immediately some stratigecially placed vanes and plenum chamber shapes would fix this problem. To be clear, our aspirations were to get at least as much cooling out of the centermount housing as a common doghouse might deliver. No miracle claims. Just good cooling combined with the assets of the centermount housing.
We chose the Porsche Type 547 engine's blower housing as our model. The 547 actually contained two fans in tandem, and had air intakes for them on both sides of the housing.
Our test track was Sebring Florida, a warm 80 degree F. even with December on us. The weather was dry, winds were light, and clouds were thin to nonexistent. Getting the insert to the track was the last step before being ready to market it. And the test went fine. No overheating, no vibration, no whine or whistling.
Head and oil temps, which vary for all of us, stayed within our normal range.
The insert is a success.
The End