Repairing Dragster Cylinder Heads*

Three Dimensional Flow Optimization *

It is hard to imagine. Traveling one-quarter mile from a standing start is less than five seconds (with top speed exceeding 300 MPH). Yet, this is how drag racing's National Top Fuel Champion Shirley Muldowney, has
made her living for twenty years.

The required horizontal uniform acceleration to accomplish this feat is nearly two times the acceleration due to gravity generated by an engine that burns nitromethane. Until recently, breaking the five second, 300 MPH barrier was rare. The improvements in time and speed can be attributed to incremental improvements the engine air flow path. This path consists of five sections, the intake manifold, the intake port (in the cylinder head), the combustion chamber (the top of which is formed by the cylinder head), the exhaust port (again in the cylinder head), and the exhaust manifold. Each port is a short tube that joins the intake (or exhaust) manifold to the intake or exhaust valve at the top of the combustion chamber.

Computer Numerical Control (CNC) machining of the intake and exhaust ports has accounted for the lion's share of the improvement. Previously, ports were ground by hand --- a long and laborious process carried out by highly-trained ``porters'' who learn their trade through years of experience.

The story would end here, except that, in the process of squeezing 5000 plus horsepower from what is essentially a 200 or 300 horsepower passenger car engine, competitors frequently burn up (literally) portions of an engine's cylinder head. And, since each of these 30 pound pieces of aluminum cost upwards of  $5000 (two per engine), repairing thedamage is of major interest.

In addition to producing their own racing heads, Total Flow Products (TFP), offers cylinder head repair services to the drag racing industry. More often than not, this repair process involves welding back burned cylinder head metal and replacing valve seats. It is generally not possible to return the engine valves to their original locations. Valve positions are moved axially, slightly but significantly, in the repair process. Such repairs leave a large amount of rough metal to be removed so that the repaired cylinder head preserves the original combustion chamber volume and smooth air flow path. The state of the art in cylinder head repair today still requires the efforts of a skilled porter to grind the air flow path to its original maximal flow condition.

The goal of this project is to automate this final porting of the repaired cylinder head. Taking as input the new valve positions and the CNC-machining data for the original cylinder head, it is desired to generate new CNC-machining data that (1) smooths the air flow path in repair areas, and (2) optimizes the shape of the new surface for maximal air flow.

The ideally completed project deliverable would be a software program that can produce the above mentioned CNC-machining data file.

 

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