GT40 headers, transaxle and oil pump

Several GT40 projects: recreating parts nobody makes anymore, fixing the original designs’ weak points, and keeping the original look.

Headers and megaphones

From a 3D scan to a finished set of headers

The headers, megaphones and a Ford 427 FE engine were 3D scanned first, as references for CAD. Using the 3D scans, the header tubes were drawn to stay as close as possible to the original design. The tubes were optimized for equal lengths and for spark plug and valve cover access, while still fitting the required footprint, and for 1D CNC bending wherever possible.

Weld fixtures were designed with keep-away areas so every component lands in the same place every time. A mock engine fixture holds the runners for fabrication and back purging while welding, and a collector reference plate bolts to both the real engine and the mock so the runners stay in their correct positions. In the tight spots, the upturn runners were 3D printed first to confirm clearance to the chassis and the position of the chassis notches for future builds.

The routing had been laid out with the straight lengths the tube bender said it needed between bends, but most tubes came back with longer straights than designed. Six of the eight tubes, and the upturns on the other two, were fabricated by hand to the design. The prototype was tack welded from the collectors to the heads and sent to the customer to verify fit. The customer finished the welding there and polished the whole assembly. To keep the original look, they built the turn-down into the megaphones as a 15° pie-cut section rather than a small 15° bend.

3D scan of a Ford 427 FE engine and original GT40 header — Engine and original header, 3D scanned.

GT40 header tubes routed in SolidWorks — Tubes routed in CAD using the 3D scan as reference.

Header 3D scan overlaid on the new CAD tubes — 3D scan over CAD to check the routing.

Mock engine weld fixture holding eight header tubes — Mock engine fixture with the eight-tube positioner.

Weld fixture for the collector and megaphone — Collector and megaphone fixture.

3D printed upturn runner test-fitted in the chassis — Printed upturn checking chassis clearance.

Bent stainless tubing for the headers — Bent tubing as it came back from the bender.

Shop-made angle tool on a stainless U-bend, reading 90 degrees — A shop-made tool for marking U-bend cuts: zero the angle finder, swing it to the angle needed, mark, and sand to the line for a cut accurate to 0.1°. This one reads exactly 90°.

Header tubes tacked together on the fixture — Prototype tacked up on the fixture.

Finished GT40 headers from the rear — Finished and polished by the customer.

GT40 headers installed in the car — Installed in the car.

Transaxle

Transaxle cases from 1960s drawings

Transaxle components were drawn in CAD from 1960s drawings. The raw castings were then 3D scanned and the 3D scans overlaid on the CAD to verify sizing and make sure every machined face would clean up. The overlay caught core shift at both differential bearing bores, which would have scrapped castings machined to nominal. The CAD is used to machine the raw castings.

Green cylinders in the overlay extend from each machined face out to where the raw casting surface actually is. They went to the machinists as touch points: where each cutter should expect to meet raw material, so it does not crash into the casting on an expensive CNC machine. The core shift left a crescent of uneven material around both differential bores. At about two o’clock the machined bore came almost to the edge of the raw casting, and that is where the machinists started referencing the part’s position.

Full-size 3D prints of the cases helped plan CNC machining and fixturing, with touch points added for the expected raw casting faces as starting references.

CAD model of the GT40 transaxle — Transaxle assembly in CAD.

Raw casting 3D scan overlaid on the differential case CAD with green touch-point cylinders — Raw casting 3D scan over CAD. Green cylinders mark where the cutters meet raw material.

3D printed gear and differential cases — Printed cases for machining and fixture planning.

Oil pump

Root cause, redesign, then a test rig

The original transaxle oil pumps wore out quickly. One half of the pump ran reversed, pulling vacuum on the bearings instead of feeding them oil, which starved the gear faces until they cut into the housing.

The pump was redesigned for CNC machining around those shortcomings, with a period-correct look: arrows, lettering and finish matched to the original. To prove it without risking a transmission or a race, Atrick Design built an endurance rig: a PLC drove a VFD through a Le Mans lap’s RPM and shift profile, with a swap plate for testing different pump modules. After testing, the teardown showed the pump in good condition.

Worn original oil pump parts showing gear damage — The original pump, worn from oil starvation.

Section view of the redesigned oil pump in CAD — Redesigned pump, section view.

CAD model of the oil pump endurance test rig drive — Endurance rig drive, in CAD.

Bellhousing and starter

A bellhousing casting designed from scratch

Unlike the transaxle cases, which were drawn from existing 1960s drawings, the bellhousing was designed from scratch as a new casting. It fits the bolt pattern Ford uses across its Modular engine family, so modern fuel-injected crate engines can be swapped in. The casting and the machined part are modeled separately, so the foundry and the machinist each work from their own model. An offset starter was designed to work with the bellhousing and a smaller-diameter flywheel.

New bellhousing casting design in CAD — The bellhousing casting, as cast.

Bellhousing with machined faces highlighted in CAD — The same casting with its machined faces.

Offset starter motor with a black mounting plate — The offset starter.

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