my stock 327 with 40's sounded good but when I went headers built 357 the 40's became obnoxis on the fwy. yelling to talk with anyone in car. The Flowmaster FX though tamed it down without making it to mellow...for me
https://www.summitracing.com/parts/flo-71226
411 chart on FlowMaster mufflers
https://www.holley.com/brands/flowma...flowfx_series/