Connect the plenum to each intake port at the length that tunes the intake pressure wave to the target engine speed.
Four runners with bellmouths at the plenum end and injector bungs partway down. Length is set by pressure wave tuning: L = (Effective Cam Duration x C) / (RPM x RV x 2 x 6), with the speed of sound C calculated from fluid properties pulled from drive data.
CR26I targeted a VE boost around 11,000 to 14,000 rpm with 5.35 in (135 mm) runners. Bellmouth design and runner taper are both evaluated with CFD and physical flow bench testing.
Machined (6.5 hours on CR26I against 16 hours on CR25), with bellmouth molds machined separately (2.5 hours) and bellmouths laid up and bonded on. Injector bungs machined (3 hours) and welded rather than bonded, using a coping fixture in the mill.
CFRP bellmouths, aluminium runner bodies and injector bungs. OEM boots retained (292 g). From the cost report drawings and CAD: From the cost report drawings: 6061 AL (Final Runner Assembly).
Fault Vault, 2023-07-27, CR22, Fundamental System Understanding, Complete Failure. The intake runners cracked at the base, with EGTs running high at idle and the engine idling at 0% throttle. Recorded options: coat the cracks with Hysol 9460, use softer rubber isolation, or get new runners printed. Mounting the plenum to the OEM runner boots from CR26I isolates the runners from engine thermal and vibrational input, which addresses the root cause.
Mounting the plenum to the OEM runner boots isolates the runners from the engine's thermal and vibrational input, which addresses the root cause of the CR22 runners cracking at the base. Injector bungs moved from bonded to welded using a coping fixture in the mill.
Dimensions called out on the cost report drawings. These are the figures printed on the drawing, not a labelled specification; open the drawing itself for what each one refers to. Final Runner Assembly (as drawn): 8.26, R0.83, 72.39, 7.24, 121.53, 12.15 22.232.22, 40.13, 4.01 CR25 Runner Tray Drawing (as drawn): 317.22, 31.72, 51.73, 5.17, 95.50, 9.55, 58.53, 5.85, 65.306.53, 47.75 Runner (as drawn): 12.15, 0.92 Source: Cost report drawings: CR25/Powertrain/Design/Manifolds/Intake/3 ~ Documentation/Cost Report Drawings/Final Runner Assembly.pdf; CR25/Powertrain/Design/Y - Cost Report Drawings/Manifolds/Intake/CR25 Runner Tray Drawing.pdf; CR25/Powertrain/Design/Y - Cost Report Drawings/Manifolds/Intake/Runner.pdf; CR26i/Powertrain - IC/Design/Manifolds/Intake/3 ~ Documentation/Cost Report Drawings/Final Runner Assembly.pdf and 4 more Quantity per car, as costed: 4
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