Racing Services

Racing Services -> Prototype Gestation

The Need

A means to separate the hot air in the engine compartment from the intake air. The original GT40 had four Weber carburators. These carbs were separated from the intake manifold by a Turkey Pan which also served to seal the engine compartment from the intake air compartment on the GT40.

The Xtreme Classics GT40 has Hilborn Electronic Fuel Injection and there is no separation between the intake stacks and the manifold as in the original car. Simply copying the original Turkey Pan would not work.

First Thoughts

Create a pattern to match the offset of the injector stacks and cut it into a flat piece of construction paper. Then tweak the paper model until it's right and transfer it to a sheet of aluminum. OK so it wasn't quite flat so we made a very shallow pan.

This looked good so we made another out of sheet metal to allow us to test the design before proceeding with a high quality finished product. Insert the MAT sensor and go for a ride. The results were good from a MAT standpoint and decreased intake temperatures by more than 60 degrees F. Still the design failed because it left the intake stacks and fuel rails "in the heat" of the engine compartment.

Second Thoughts

Can we create a 4 sided pan and use the lifter valley cover as the base of the pan? This would be nice because it would keep the stacks, the rails and the fuel lines all in the cooler air. This is a bit more complicated than the nearly flat original idea so let's start with sketches. (Hey it's better than a napkin)

Next these dimensions will be used to create a CAD drawing. Once the CAD drawing is complete another construction paper model will be constructed. Keep in mind we have the engine cowling interference to deal with but here's the first model.

Sweet so far. All that good stuff is now isolated from the heat in the engine compartment plus it's shielded from the extreme infra-red of the exhaust. Still the front area needs to be modified so the engine cowling will close properly. After a few iterations we come up with the design that seals out most of the heat and just clears the engine cowling when it's closed.

It's quite obvious at this point that the pan must be installed in two pieces so it's determined the left side and the rear panel should be welded and the front and right side panel also be joined. Next task is to lay this out on sheet aluminum (minus bend allowances), shear it and then mill out the slots needed for the different aparatus clearance. Then form the bends and weld the 4 pieces into 2.

The finished pieces are fastened together in situ with blind rivits. On the road the turkey pan functions well. The MAT sensor now reads ambient air temperature as cool outside air now fills the area above the injector stacks. Hot engine compartment air is no longer feeding in from below. Now that we have a stable MAT we can finish tuning the EFI fuel maps.