I want to get the flowmaster on my 92 firebird it has a 305 TBI which would be louder the 40 or 80 series flowmaster?

 

The regular 40 is probably a little louder although you did not specify on the 3 types they make. 80 will be similar and look better. Both sound terrible, drone like crazy and are going to be amusing on a 17 second TBI car.

 

Not sure about 40 series fitment in the third gen but 80series is perfect. Lol at the reply above. I like the sound of my car and it's not loud at all. If you come from carbs and two muffler system cars, these things 'barely' drone. Anyone who says flowmaster 80 series drones and is too loud has never driven a two muffler system car. And honestly I disagree with sound being funny on a slower older car. Being that guy who WOTs to every stop light, bobs and weaves through traffic is much more hilarious/annoying.

That being said, find some videos online first to attempt to find a sound you like. If the 40 would fit, its def louder

 

The 40 series is their standard muffler, the 80 series is their crossflow (single in, dual out, one on each side of the muffler like the stock muffler). The 80 is louder and flows worse, but does keep the stock layout with a tailpipe on each side, the 40 is mellower and without some fancy plumbing will pretty much take you down to a single tailpipe on one side.

Neither flow as well as a decent straight through design, OTOH, they will all be OK on most 305 TBI cars

 

The Crossflow 80 series is designed for our cars and is loud.
I have one = (system)
Here's a chart I found on there site.

 

I don't think my 3in system with the crossflow 80 series is that loud nor does it drone very bad either. It sounds great and ive ran almost every type of muffler on these cars from glasspacks to Borla. Hands down Borla sounded the best. In saying that i am very happy with my Flowmaster 80 series on my "17 sec TBI car" lol.

 

Let me rephrase that.
Its loud on my car.
Could be the cut back tail pipes. They are under the rear some as apposed to at the outer edge of the rear bumper cover when it was first installed.

I really like my American Thunder Cat Back as well.
I actually prefer to listen to it while I'm driving as apposed to the stereo.

 

i have 80 series on my trans am and they sound awesome