Machining a twin-scroll turbocharger package for a trackday roadster in Wareham
A Rhode Island track builder brought us a custom lightweight roadster chassis experiencing severe boost threshold lag and cracked collector flanges on a cast manifold purchased online. The unbranded cast iron unit suffered 0.8 mm surface warpage under exhaust gas temperatures exceeding 870°C. That distortion warped the turbine housing flange, leaking unmetered exhaust pulses into the engine bay and scorching the main wiring loom.
Teardown began by fixturing the cylinder head on our Wareham surface plate. The replacement assembly paired a 58 mm billet compressor wheel with an Inconel 718 turbine wheel inside an A/R 0.82 housing. The collector was fabricated from 321 stainless steel runners with equalized lengths within 4 mm across all four cylinders. Each runner was purged with 99.99% argon and back-shielded during TIG welding to prevent internal sugaring.
Mating flanges were machined from 12 mm hot-rolled 304 plate, surfaced to 0.02 mm total indicated runout. Custom grade 10.9 zinc-nickel flanged fasteners were installed and safety-wired directly to the turbine scroll, ensuring thermal expansion cycles never loosen the collector studs under sustained 1.6 bar track boost.
Fixtured on Wareham granite surface plate datum A-B. All runner centerlines plotted to equalize pulse arrival at turbine scroll within 1.2 milliseconds at 6,400 RPM. Flanges surfaced on horizontal milling center before TIG pass.
