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I'm building a recreation 70 conv judge RAM AIR IV out of a 242 conv and now I'm buying all my parts. Exhaust is next on the list. I would buy them from Ames Performance like I did for everything else unless someone knows a better place for parts. If I go with OEM I'm looking at 2 1/4, aftermarket with flow masters is 2 1/2. If I go with aftermarket vs the stock OEM exhaust what differences would I be looking at when it comes to sound, performance and fit?

Also what is the difference between a RAM AIR exhaust vs. the NON RAM AIR exhaust besides the fact that one goes on a RAM AIR and one doesn't. Basically are the two exhaust systems interchangeable? I can buy a complete NON RAM AIR aluminized system with mufflers for $250 brand new from a friend that bought it for his 70 goat with a 455. Would that system bolt up to a RAM AIR IV motor?
 

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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.
 

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Since your car is not going to be original and correct anyway, I would definitely run 2.5. I have that on my 428 69 with the Dynomax mufflers and they sound very deep but not too loud. I had some Flowmaster knock-offs on first and they were so loud I couldn't stand it.

I would make sure there are factory-style tips available for the 2.5 although an exhaust shop could probably expand the smaller ones to make them fit.
 

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Thanks for the help guys. I just heard a 69 gto and it had a 455 with 2.5 inch pipes with an X pipe along with the ram air exhaust manifolds. He had 40 serise flows masters on his and it was pretty loud driving around. Sounded great outside the car but I couldn't hear the engine over the exhaust inside the car. I'm not one to look at my tach while having a little fun with the car so I'm going to try out a little more quiet muffler.
 
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