I just installed a flowmaster 80 series muffler on my 1991 base firebird with a 305. its listed right between aggressive and moderate on the flowmaster sound chart. there are a couple small hiccups to deal with when you install. the flowmaster has 2.5inch inlets. it also has 2 outlets where the stock is a single tail pipe. I had to use a couple of couplers and an adapter but it wasn't bad. would have been much easier had I planned it all out first. had to go to the parts store three times. the exhaust has a much better rumble without being loud. you can HEAR it but its not obnoxious or annoying. ive only driven about 10 miles on it but I like it a lot. I really disliked the stock exhaust sound. there is more interior drone than before but not enough to bother me. I suggest it for anyone looking for a good sounding muffler for a driver.

 

Congrats,I like my 80 series as well.I know most people don't like them but that is a very popular muffler for our cars.

 

I think it has a good sound. aggressive but not annoying. I like it

 

 

I've been rocking the 80 series for the last 20 years. I love it. It's my car's sound for almost as long as I've owned it. And it'll trap 117 mph in the quarter. So it's not all bad for performance. Maybe I'd get a couple more mph with a different muffler, but it's not worth the sacrifice IMO.
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Make sure it's wrapped going past oil pan.

 

I also have an 80 series on my 82, but it's 3" offset inlet with dual 2.5" out. I run a 3" primary pipe. Flowmaster 43083 80 Series. It has a real nice sound, but when you have a 3-speed transmission and 3:42 gear, cruising at 60 mph, it gets old real quick.

 

+1 for that. When my headers went on, my oil pressure would drop down to under 5 psi when idling in traffic on a hot day -- the pipe was heating the oil so much that it couldn't sustain pressure because it viscosity had gone out the window. I ended up getting the y pipe redone and to be safe and as a preventative measure, swapped in a new oil pump and ran thicker oil. Problem solved, but scared me real good when it first happened!

 

Love the sound of mine. 3in inlet 2.5 outlets, no cat. Got a video of it on youtube "dmccain" . I hear people bash them but the sound is great.

 

Love my Flowmaster 80's

Idle and quick Rev

Wide open

 

This is my car when I had the 80 series on it. carb'd 383 stroker, dyno dons headers and 3" to the muffler, the muffler was a 3" in, 2 1/2" out. My iphone mic wasn't able to really pic up how loud it was.