Bring the car's sound emissions under the competition limits without adding backpressure or weight.
A 16 inch single-pass, fiberglass-packed titanium muffler with a 14 inch perforated tube. The perforated tube surrounds the flow path so exhaust gas is never forced through the packing, which keeps backpressure low while the packing still absorbs sound energy and turns it into heat. Length is set by quarter wave tuning at 11,000 rpm, the sound test speed.
Absorptive rather than reactive. Absorptive is typically heavier because of the packing, but it lowers sound at all frequencies, has simple geometry and gives lower backpressure; reactive is lighter but targets specific frequencies, needs complex geometry and raises backpressure. The 2 inch inlet is the only available size for titanium perforated tubing; the 1.5 inch outlet into the tailpipe was experimentally shown to reduce noise emissions below the sound test limits.
Sound targets: 103 dBc at idle, 110 dBc at 11,000 rpm. Must mount without putting a moment on the secondary v-band, and without interfering with the aerodynamic package.
Prototype sound tested by installing a CR25 prototype muffler on CR22 and sweeping muffler length (14 in and 16 in), packing density, tailpipe geometry (2 in and 1.5 in diameters) and a diffuser style exhaust tip, so compliance was proven before the design was finalised. From the design reports and one-pagers: Muffler design starts from a measured exhaust gas temperature inside the muffler of 672 K. Below roughly 8,000 rpm it is unreasonable to build a muffler long enough to cancel the sound waves, which would need to exceed about 20 in, so packing has to absorb the idle sound instead. At 11,000 rpm the waves can be destroyed with the correct quarter wavelength, which lands at around 14 in. That split is why the muffler is a hybrid: packing for the low end, a tuned tube for the sound test speed.
CR22 build sequence with logged times: cut the perforated tube to size (15 min); waterjet the flat panels and bolt flange (1 hr); cut the 4 in tube to length and in half (1 hr); bolt the flange to the jig and tack weld the perforated tubes (45 min); tack weld the inner baffle to the top of the perforated tubes (45 min); tack weld the half-tubes to the sides of the flange (30 min); tack weld the long side panel (1 hr); tack weld the short side panel (45 min); weld the inner baffle to the sides (1 hr); tack weld the top short side panel (30 min); tack weld the top cap (45 min); seam weld throughout (2 hr). Muffler bolt-on plate: CNC mill (2 hr), weld the V-band flange (30 min), weld the exit pipe only after mounting on the car with the tire fitted to confirm position (1 hr). Muffler gasket waterjet (30 min).
CP1 titanium shell and perforated tube, 1 lb of fiberglass packing at 0.006 lb/in^3 packing density. Mounted to the frame via a silicone exhaust bushing. From the cost report drawings and CAD: From the cost report drawings: CP2 TITANIUM (CR25 Muffler 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.
16 inch overall length, 14 inch perforated tube length, 3.30 lb packed. 71% (8.2 lb) lighter than CR22's muffler. From the design reports and one-pagers: CR22 muffler: 1.25 lb of fiberglass packing to bring idle down to 103 dBC, a 14 in internal tube giving destructive cancellation at 11,000 rpm while preventing the packing obstructing flow, a flange at the bottom so the packing can be removed and replaced, an outlet pointed away from the ground to minimise ground interference during sound testing, and a frame tab mount. 7.5 lb without packing. The CR25 titanium one-pager targeted 3 lb with packing against CR22's 11.5 lb, a stated 8.5 lb loss, at a total system cost of $393.55 and 2 to 3 weeks of welding and fabrication once parts arrived. 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. Baffle (as drawn): 74.74, 49.15R49.15, 48.79, R48.79, 0.36, 51.56, 173.04, 0.76 Muffler Batting (as drawn): 74.74, 48.79, R48.79, 51.56, 101.60, 352.04 Muffler Endplate (as drawn): 24.67, 6.35, R6.356.35, R6.35, 50.80, R50.803.18, R3.18, 27.78, R27.78, 3.18 Retainer (as drawn): 6.35R6.35, 24.67, 24.67 50.80, R50.80, 28.58, R28.58, 52.39, 12.71, 14.09, 74.74 Muffler (as drawn): R5.08, R0.64 R0.64, 17.63, 47.65, 5.08, 10.86, 5.84, 55.99 CR25 Muffler Assembly (as drawn): 0.32, 0.15 0.15 0.15, 2.68, 2.54 R1.34, 1.27, 40.49, 37.62 Quantity on the drawing: 1. Source: Cost report drawings: CR22/Powertrain/Design/Manifolds/Exhaust/CR22a/4 - Documentation/Cost Report Drawings/Baffle.PDF; CR22/Powertrain/Design/Manifolds/Exhaust/CR22a/4 - Documentation/Cost Report Drawings/Muffler Batting.PDF; CR22/Powertrain/Design/Manifolds/Exhaust/CR22a/4 - Documentation/Cost Report Drawings/Muffler Endplate.pdf; CR22/Powertrain/Design/Manifolds/Exhaust/CR22a/4 - Documentation/Cost Report Drawings/Retainer.PDF and 4 more Quantity per car, as costed: 1
Nothing in CrimsonStorage covers these yet.