Assembly line covering the complete exhaust system.
Groups the primaries, collector, secondary, lambda sensor, muffler and tailpipe. Design Philosophies and Processes: Inherited from the Manifolds subsystem design process: 1. Build the engine model in GT Suite from measured geometry: silicone-cast and 3D-scanned intake ports, dial-indicator-measured cam lobe profiles, MTS-measured valve spring curves. 2. Use GEM3D to convert manifold CAD into GT Suite flow geometry, which cut manifold setup from several hours to about 30 minutes and let subassemblies be swapped for fast comparison. 3. Sweep plenum volume, runner length and primary length in the model against volumetric efficiency. 4. Confirm on the flow bench. CR26I plenum flowed 2.34% more than CR25 and 11.15% more than CR22 on average across 10-50 in-H2O, with testing extended to 70 in-H2O (17.4 kPa) to reach WOT conditions. 5. Prototype-test the muffler on the previous car before finalising, sweeping length (14 in and 16 in), packing density, tailpipe diameter (2 in and 1.5 in) and a diffuser-style tip against the sound limits.
The subsystem process above covers the GT Suite side. The older Sphinx wiki exhaust page adds the component-level sequence the system was designed against. It carries no car generation and references CR20 and CR21 as the current cars. 1. Select material. Low-carbon steel is marginally lighter than stainless by density but corrodes at exhaust temperatures, quoted as roughly 1300 F. Aluminium is much lighter than stainless and will not survive those temperatures. Titanium is half the weight of stainless and twice the price. 2. Set primary length by pressure wave tuning: L = (ECD * C) / (2 * RV * 6 * RPM), with speed of sound C = sqrt(1.337 * R * T), 1.337 taken as the specific heat constant at 1000 K. The tuning assumes no change in exhaust temperature and full-amplitude wave reflection at the collector. 3. Pick the reflective value and the rpm it is tuned for. The design settled on a reflective value of 4 for a 9,000 rpm peak inside the packaging available, giving a target primary length of 11.63 in. 4. Size the primaries to hold cross-sectional area from the exhaust port through the pipe: 1.25 in diameter, with average length deviation between runners held to 0.3 in. 5. Mount on individual flanges rather than one shared flange. That change gave a 19% total weight reduction and removed 16 hours of manufacturing time, because the primaries no longer have to be sanded flush with the engine. 6. Choose the collector. Welded is not removable, needs welds to seal, gives an open volume for the primaries to dump into and runs 1.5 in diameter. Slip-fit is removable, seals by thermal expansion, needs springs to retain it and a merge bullet, and runs 2 in diameter. 7. Design the secondary by steady-state incompressible flow, using the fluid energy equation and conservation of mass, assuming constant temperature and constant mass flow across the secondary. 8. Design the muffler around its effective wavelength: absorptive packing for the low-rpm content plus a tuned length for high-rpm cancellation.
From the Sphinx wiki exhaust page: - Packaging set the primary length. A reflective value of 4 at 9,000 rpm and an 11.63 in target is what fitted the car, not what tuning alone would have chosen. - Sound. The system has to pass the sound test at idle and at three-quarter engine speed. The muffler goals are written as 103 dBC at idle and 110 dBC at 11,000 rpm. - Weight. Stay within 15% of CR21 if the muffler can be placed in the centre of the car below the engine; if it cannot, cut system weight by 10%. - Mounting. CR21's arrangement put a moment on the secondary v-band, and the muffler must not interfere with aero. - Leak paths and weld time. Reducing potential leak points and time spent welding are stated design goals. - The rpm target is 8,000 to 11,000, set by the car's gearing and by driver habits, rather than by the engine's peak.
Three analyses are documented on the Sphinx wiki exhaust page: - Pressure wave tuning for primary length, L = (ECD * C) / (2 * RV * 6 * RPM), with C = sqrt(1.337 * R * T). Effective cam duration comes off the cam profile. - A GT-Suite comparison of different primary lengths. This is listed as a goal for the primaries, not as a completed result. - Steady-state incompressible flow through the secondary, using the fluid energy equation with pump, turbine and loss heads, plus conservation of mass, and assuming constant temperature and constant mass flow. Comparing CR20 (1.5 in v-band tapering into a 2 in secondary, muffler on a bolted flange) against CR21 (taper eliminated, muffler on a v-band) gave a calculated backpressure reduction of 3.37 kPa, 72%.
Stainless primaries, CP1 titanium secondary, muffler and tailpipe. From the cost report drawings and CAD: From the cost report drawings: 304 Stainless Steel (CR25 Exhaust Primary Assembly); CP2 Titanium (Exhaust Secondary); Mild Steel (CR26i Exhaust Primary Assembly).
None recorded. This part has no entry in Knowledge_Transfer/Issue Logging/Fault Vault.xlsx, in either Issue Log.xlsx, in CR22/Issue Tracking/Shakedown 7-15-23.xlsx, or in any design review issue list found in CrimsonStorage or Box.
From the Sphinx wiki exhaust page, both what it records as done and what it asks for next: - Individual mounting flanges replaced the shared flange: 19% total weight reduction and 16 hours of manufacturing time removed. - CR21 eliminated the taper from the 1.5 in v-band into the 2 in secondary and moved the muffler to a v-band mount, calculated at 3.37 kPa (72%) less backpressure than CR20. - Still open: mount the muffler so it does not see a moment at the secondary v-band, keep exhaust gas out of the packing by surrounding the flow with perforated tube rather than passing it through packing, and hold weight flat against CR21 or 10% below it. - The muffler the page describes is 1.25 lb of packing and perforated tube for low-rpm sound waves, a 12 in section for high-rpm wavelength cancellation, a large back volume to reflect sound back down that 12 in tube, and a flow path uninterrupted by packing or baffles.
CR26I reduced exhaust weight by 4055.63 g (8.94 lb) against CR25's 4843.14 g total; CR22's total was 8898.77 g. The secondary alone is 62% (1.26 lb) lighter than CR22's. Switching from 304 stainless to CP1 titanium from the secondary through the tailpipe gave a 43% density reduction (CP1 Ti 4.51 g/cm^3 against 304 SS 7.93 g/cm^3). From the cost report drawings and CAD: 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. Exhaust Flange (as drawn): 3.18, 8.26, 6.35, 44.96, 38.10, 29.97 CR25 Exhaust Primary Assembly (as drawn): 69.60, 6.96, 29.97, 3.00, 72.61, 7.26, 72.48, 7.25, 51.56, 5.16 Exhaust Secondary (as drawn): 69.60, 6.96, 51.56, 5.16, 50.80, 5.08, 65.09, 6.51, 76.20, R7.62 CR26i Exhaust Primary Assembly (as drawn): 69.60, 6.96, 29.97, 3.00, 72.61, 7.26, 72.48, 7.25, 51.56, 5.16 CR26i Exhaust Secondary (as drawn): 69.60, 6.96, 51.56, 5.16, 50.80, 5.08, 65.09, 6.51, 76.20, R7.62 Quantity on the drawing: 1. Source: Cost report drawings: CR22/Powertrain/Design/Manifolds/Exhaust/CR22a/4 - Documentation/Cost Report Drawings/Exhaust Flange.pdf; CR22/Powertrain/Design/X - Cost Report Drawings/Manifolds/Exhaust/Exhaust Assembly.pdf; CR22/Powertrain/Design/X - Cost Report Drawings/Manifolds/Exhaust/Exhaust_Assy.pdf; CR25/Powertrain/Design/Y - Cost Report Drawings/Manifolds/Exhaust/CR25 Exhaust Primary Assembly.pdf and 9 more
Nothing in CrimsonStorage covers these yet.