Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
Mentioned: 1 Post(s)
Tagged: 1 Thread(s)
Quoted: 364 Post(s)
Hmmm, good question. Let me be the first to try and respond - my opinion only here on this.
First, with a 455CI, I would be using 2 1/2" pipes. I like 3" pipes, but that is my preference and I usually don't run tail pipes, just turn downs at the back of the muffler. I want people to know what I have. I use Dyno Max.
They make the Ram Air cast iron exhaust manifolds having 2 1/2" outlets or 2 1/4" made by Ram Air Restoration Enterprises. I'd go with 2 1/2" on these.
The factory non-Ram Air exhaust manifolds are not as streamlined and don't flow as well. You would also be restricted to the smaller pipe size. Not recommended in my opinion.
I suspect that the flanges that fit the exhaust pipe to the exhaust manifold are different in shape between the 2 1/4" Ram Air manifolds and the stock non-Ram Air manifolds and the outlet angle/position is different.
I would also recommend the Dr. Gas "X" style exhaust crossover pipe as part of whatever system you select. This helps your exhaust flow and balance of it, and will help lower sound levels.
For sound, the larger the case the quieter it will generally be. Getting my info from the Jim Hand Pontiac book, he selected the DynoMax Ultra Flow part #17288 for his 455CI wagon which he races and drives on the street. Dimensions are 4.25" x 9.75" x 20". He test 23 mufflers for flow and sound. The OEM muffler was indeed a big loser in flow, but slightly quieter -I would not use these at all. The DynoMax Super Turbo #17749 had slightly less flow and a little bit quieter. Overall, most performance mufflers were fairly close. Resonators can also be used to bring down the noise if you choose to.
There are suppliers who can make a complete system ready to install. Hand recommends in his book the Pypes Division of Performance Years.
I think U-tube has a video that compares muffler sounds that you can hear if that helps any.
Hopefully you will get some other opinions.