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Discussion Starter #1
'67 335hp automatic convertible

Not sure what inlet/outlet size I should order, since I don't have a welder and cant take off what's on it.

OD of both the inlet and outlet exhaust pipes on it now measure 2.45". Does that mean the inlet/outlet of the muffler itself is 2.25? or is the muffler sold to accommodate the pipe size to go on it, meaning I get 2.5" and the actual 2.45" is just slop?

Sorry, not an exhaust person. I'll be taking this to someone to weld up. But, I need to order all the stuff to take in.

thanks.
 

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Reading your description, sounds like your head pipes & tailpipes have been replaced over the years. How long a case muffler are currently being used? In the early 80's I used to order Sonic Turbo mufflers. They flowed the best & were not annoying sounding, but I was not up against the threshhold of installing them under vehicles whose engines were making 450-500 gross hp. The short case Sonic Turbos worked great under the short bed Chevy pickups & A-body's my buddy's & I were tinkering on at the time. Your mufflers may be something similar.

A bone stock std horsepower '67 GTO would have come with 2" head pipes & 2 1/4" tailpipes. Original 400 HO & RA equipped '67's received 2 1/4" headpipes as well as 2 1/4" tailpipes. Original mufflers were offset side (inlet next to the driveshaft) with offset side (outboard side) outlets. If you are after bone stock type set-up complete with tight bends & flat spots, can either have a longtime muffler shop operator equipped with a card system, hand bend an exact copy of the stock exhaust system made with aluminized steel. The system will not be mandrel bent, will have tight spots in the bends. One can also purchase the same kind of stock bent system from Gardner Exhaust with their proprietary different case length mufflers & clamps, expect a $1000 plus expenditure.. On a high level restoration, that one's willing to give up hp/torque numbers, that is an option. Am beyond anal on my own restorations, but am no way willing to leave on the table, the amt of hp/torque in a restrictive stock kink bent exhaust system.

For many years, have used the 20" case 2 1/2" offset inlet/offset outlet Dynomax mufflers, they are hard to beat free flowing long oval case mufflers. 20 years ago, for my own projects I'd order the 2 1/2" inlet/outlet Dynomax CVX 17205 mufflers (aluminized version of the same size stainless Ultraflow), eventually I started ordering the Dynomax 17449's. For quite a few RA manifolded projects, have started off my own head pipes utilizing mandrel bent "drops" made of 2 1/2" U bend tubing. After the drop, there is a TIG welded seam where the head pipe begins its way rearwards. Basically, the exact same method Pontiac used on it's '73 & '74 455 SuperDuty head pipes. In an effort to have seamless unwelded mandrel bent 2 1/2" head pipes & tailpipes for '70's, 71's, & 72's , a solution is being worked on. One that hopefully many Pontiac owners will like to purchase ;)
 

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Thanks for the info. This is not a show resto. Just a numbers driver freshen up. I want to keep it looking stock, because I like it that way. And, nothing crazy so it still has points/show potential if I ever decide to do a frame off or sell it.

The dead giveaway on the exhaust was no resonator. And upon further inspection 2" pipes out the back.

It looks to have sonic turbos on it now....offset in/center out. And, they do sound ok. But, I found a pair of used magnaflows for cheap that should slide right in with little effort...if the 2.5" pipes will slide over the 2.25" stubs. And, I do like the sound of Magnaflows on Fords. Never heard them on a poncho personally, but the few YouTube videos I've found they seem to have a nice tone.

But the 2" pencil tips will have to go. I may just have a 45° turndown at the mufflers if my shop can't do a clean bend over the axle with 2.5" pipe.
 

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Reads like whatever muffler fits is going to be your solution. Over the years, tailpipes often get replaced along with mufflers, so going to a muffler that has a wider or narrower spread between the centerline of the inlet & outlet of the muffler, will often require tweaking or replacement of the headpipes or tailpipes. Decently bent exhaust systems are not something that typically get dinked for points at shows.
 
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