I use a Spintech part number 343SC . Its a 13"L Crossflow muffler 9" high 4" W. It has a single 3" inlet and two 2 1/2" outlets. If you want something quieter call Spintech and specify a 2 1/2" inlet and two 2 1/4"" outlets that can be connected to the Fiero trumpet exhaust ends. Spintech mufflers emit a deep sound but they are quieter than the Flotech afterburner muffler that is super loud. With the afterburner it was so loud inside that you couldn't even converse on the highway while cruising. If you want to quiet the Spintech some, wrap both exhaust pipes in DEI exhaust wrap. The pipes will act like resonators.
------------------ " THE BLACK PARALYZER"
-87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
[This message has been edited by Dennis LaGrua (edited 10-18-2020).]