it should be plenty loud with straight pipes & the converter still on it.
but it wont make any noticeable difference in the gas mileage
I've had a 1500 4x4 with the 5.9 for 12 years, ran it with the stock converter , hollow torpedo muffler & duals for 6 or 8 years it was pretty loud & got 15 to 17 hi way mileage.
completely gutted the converter welded it back up & put it back on after it started rattling.
didn't change the gas mileage at all or the sound much & no problem with the check engine light.
put the stock muffler & stock single pipe back on when the duals rusted out.
got a lot quieter except for a harmonic resonance at exactly 2100 rpm (sounds like the heat riser buzzing) but no change in gas mileage & still no problem with check engine light but I did have to change both 02 sensors at around 120,000 to 140,000 miles when the light came on. cant remember for sure but I think I still had the duals with the hollowed out converter at that time, anyway the check engine light went back off after I changed both sensors & Still hasn't came back on at 170,000+ miles.
CAT Catalytic Converter Pipe Accord 98 99 00 01 02 L4, CAT Catalytic Converter Pipe Civic 01 02 03 04 05 EX, 09 10 11 2009 2010 2011 GSXR1000 GSXR 1000 Exhaust Mid Pipe Catalytic Converter, 00-09 HONDA S2000 CATALYTIC CONVERTER STRAIGHT PIPE, 01-09 S2000 CATALYTIC CONVERTER REPLACE STRAIGHT PIPE, 03-04 Corolla Vibe Matrix FWD High Efficiency Catalytic Converter Exhaust Pipe, 05-07 Lancer 2.0L Rear Underbody Flex Pipe and Catalytic Converter NEW, 79-04 Mustang H pipe with High Flow catalytic converters with ball socket , 09-12 Yamaha YZF R1 Catalytic Converter Cat Eliminator Mid decat Y Pipe CA1, Kawasaki ZX10R ZXR 08-10 Catalytic Converter Cat Eliminator Mid decat Y Pipe CA5, HONDA 90-93 ACCORD HIGH FLOW CATALYTIC CONVERTER PIPE, CAT Catalytic Converter Pipe Integra 94 95 96 97-01 GSR, 2003 NISSAN ALTIMA 3.5L Y-Pipe Assy. Weld Clamp Fit Catalytic Converter Warranty, 1996 CHRYSLER SEBRING 2.5L Front Eng. Code N Y-Pipe Assy. Catalytic Converter, 1997 CHEVROLET 1/2 TON 5.7L Dual Y-Pipe Direct Bolt On Catalytic Converter NEW, 1998 GMC YUKON 5.7L Dual Conv. Y-Pipe Assy. Direct Bolt On Catalytic Converter, 1999 FORD TAURUS 3.0L Front Eng. Code S DOHC Y-Pipe Assy. Catalytic Converter, 1998 FORD TAURUS 3.0L Front Eng. Code S DOHC Y-Pipe Assy. Catalytic Converter, 1996 DODGE AVENGER 2.5L Front Eng. Code N Y-Pipe Assy. Catalytic Converter NEW, 1997 CHEVROLET 1 TON 5.7L Dual Y-Pipe Assy. Direct Bolt On Catalytic Converter, 2000 CHRYSLER SEBRING 2.5L Front Eng. Code N Y-Pipe Assy. Catalytic Converter, 1994 FORD ESCORT 1.9L W/O EGR fitting on Outlet Pipe Clamp Catalytic Converter, 1994 FORD ESCORT 1.9L W/ EGR fitting on Outlet Pipe Clamp Catalytic Converter, 1994 GMC TRUCK YUKON 5.7L W/ Conv. in Y-Pipe Weld Clamp Fit Catalytic Converter, 1997 GMC 1/2 TON 5.7L Dual Y-Pipe Assy. Direct Bolt On Catalytic Converter NEW, 2000 DODGE AVENGER 2.5L Front Eng. Code N Y-Pipe Assy. Catalytic Converter NEW, 1994 CHEVROLET BLAZER 5.7L W/ Conv. In Y-Pipe Weld Clamp Fit Catalytic Converter, 1996 GMC 1 TON 5.7L Dual Conv. Y-Pipe Assy. Direct Bolt On Catalytic Converter, 1998 GMC SUBURBAN 1/2 TON 5.7L Dual Y-Pipe Direct Bolt On Catalytic Converter, 1999 CHRYSLER SEBRING 2.5L Front Eng. Code N Y-Pipe Assy. Catalytic Converter,
