I have a 1966 tripower and wanting to put exhaust on it. Debating if i should do Pypes or Flowmaster and then 2.5 or 3 inch pipes? Any suggestions on mufflers would be awesome as well. Was looking at some of the pypes set ups and looks like they have Race Pro and Violater, not sure what flowmaster offers.
In terms of sound, i want an aggressive idle rumble and a good throaty sound when stepping on it.
Just my opinion.
Assuming factory exhaust manifolds? I would go with 2.5" pipes for several reasons. First, fitment. 3" is pretty big and they will hang lower and clearance in general will be tighter. 3" pipes will be louder as you will get a little more "echo" (sound waves) bouncing around. You need a little back pressure in an exhaust system so the exhaust does not over scavenge the air/fuel mixture during valve overlap.
Now, if you have an engine pushing over 450HP and can spin a lot of RPM's, then 3" pipes would be my choice as you want to get that exhaust flow moving. You might want to do a little mixing of your pipes like run the 2.5" head pipes to your mufflers, then run a 3" tailpipe.
I have played around with exhaust systems with all the cars I have owned and found that the placement of the muffler also contributes to the sound that comes out. The larger diameter tailpipes can change the sound. In my time it was Corvair Turbo's we all ran. They were short and had the 2.5 inlet/outlets. Length and diameter is another factor that changes sounds as well as the baffling inside - with many having their own design.
The last set of pipes I had were a 3" dia to a pair of Dynamax mufflers and turn downs in front of the rear axle. Now I just told you not to use 3" pipes, but my thinking was that I was using the factory restrictive cast iron exhaust manifolds which I felt would developed the back pressure in the exhaust system and the 3" pipes would not over scavenge the cylinders. Problems I encountered as I fab'd up my own system was that the 3" pipes were extremely close to the oil pan (I used a 3" elbow to which I welded reducers to work with the exhaust manifold outlets) which I am sure added extra heat to the oil and they hung low like headers - and yes I did hit 'em with the "bouncy" front springs I had in the car. My Dynamax mufflers had a drone about 2,000 RPM's, BUT they now advertise "Drone-Free." I liked the sound, but again, no tailpipes. I will probably go with them again with my 455CI build.
Some muffler sites have sample sounds you can listen to. You might also try You Tube and find a Pontiac having a similar system you are looking to go with or get a few ideas of what other system's sound like. Keep in mind that the cam selection and even compression ration has an effect on the exhaust note as well. Here are a few to choose from:
and check out this Firebird pulling away, it sounds pretty good too: