92/93 GT Dual or single exhaust?

[RuFF]

I dont know to much bout exhaust or mufflers but i wanna get a muffler to add some HP to my grand am. whats the difference in the 2 types of exhaust and what should i be looking for if its a dual/or single when buying an muffler. also how much would it roughlt add to HP?

my grand am looks just likes gaguy

[graden]

i know when i had my 3300 in my G.A I ran a K&N air filter and dual exhost, I was running about 165 for horses. I would have love to run true dual exhost on this car but no options were avail at that time. So I T-boned it right after the rear axel. No dyno was done but this was figured out from my time slips on the quarter mile with a horse power calc program.