I know nothing about American Pontiac motors, as such im trying to figure out why someone would put 2 in manifolds on a 455, second question can I get 2 1/2 manifolds that fit a b body chassis . and yes I know, just got it have to modify, but I have a leak and the exhaust is rotten so I need to bend up new pipes and replace gaskets

I'd suggest you find a set of shorty headers for a '75 455, the applications would be Trans Am and see if the shorty fits. The sure have the shape of cast iron manifolds 

You got a real puzzle now, a Canadian Pontiac with a US Pontiac blue block. 

CLICK HERE FOR 455 TRANS AM HEADERS

I also found this listing for a 75 Catalina which says does not fit 455 but the Hedman above says it fits 400 and 455 so who knows:

CLICK FOR CATALINA SHORTY

I don't think its a Canadian frame, this is a American body, and headers are to tight with this motor, my thought was to stick with cast just go to a bigger diameter nice and clean plus quiet.

I read this article last night when I suggested the shorties, you may glean something else from it but its all there. The reason I suggested shorties was because they very much replicate the top factory style exhaust manifolds, are easy to buy and reasonably priced. 

CLICK FOR PONTIAC EXHAUST TIPS

I do understand that headers do flow more, and yes I was up till late, my mom is in the hospital so I was waiting for a call, but my thought was cast iron just because of all the good repros on the market now for the Pontiac at a reasonable price that will far outlast the headers, I real don't wanna be doing this job again its not going to be fun.

I was more wondering what will fit in a parisienne /catilina chassis, I haven't gotten to the bottom of that yet

apparently the aftermarket ram air manifolds will work on fire bird and grand prix so that would also include fullsize chassis would it not.

I suggest RARE get a hold of them to find out if they fit your car.

https://www.ramairrestoration.com/pontiac/factory-headers.html

i was looking at there website looks like a good product, I was also looking under the hood , seems like the b body has lots of room , question I have is how in the world do you get to any bolts, and do they snap off like a ford fe motor were you finally resort to removing the heads after removing the front fenders, or is it just a mater of jacking it up, small and big block chevs are easier, just saying

Yes unfortunately, some of these 44 Years old bolt will snap off and you will have to remove the heads :(

how did I guess, every engine has a design flaw some more than others, manifold bolts are my pet peave

Sometimes its nice to pay a muffler shop to deal with the studs.

I like the idea of reproduction cast performance manifolds. I don't think any of those after the 1963 Super Duty 421 used gaskets on the manifolds, something headers have and often leak.

You're going to run the Y-pipe & single cat, right?

thanks, I always go away from factory parts, who would think a steel plate wouldn't blow out, its getting the bolts out that concerns me , I don't want to pull a head or motor for stupid gaskets, got a 390 with that issue and its still not fixed.

CdnGMfan wrote:

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Sometimes its nice to pay a muffler shop to deal with the studs.

I like the idea of reproduction cast performance manifolds. I don't think any of those after the 1963 Super Duty 421 used gaskets on the manifolds, something headers have and often leak.

 

You're going to run the Y-pipe & single cat, right?

-- Edited by CdnGMfan on Friday 21st of September 2018 12:33:04 PM

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 not for 75, its duels for the 455, and by the hangers its all original

hey Carl funny thing , got the last two carb kits in western Canada for this thing , the next two are in brampton

There is no way this car was dual exhaust from the factory, all 75's were single catalytic and single exhaust, EXCEPT the 454 Impala & Caprice had a dual system that left the converter as single then split into dual with mufflers and tail pipes. That system would undoubtably bolt right in this Pontiac. 

I don't know Ray , but from what I can see underneath, all the hangers are factory , no aftermarket, pipes could be a second set , but I wont know till I pull them.

Then the aforementioned  454 system was bolted in early on in the car's life. I even used that system on a few A bodies with no alteration except tailpipes.

65wagon wrote:

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I don't know Ray , but from what I can see underneath, all the hangers are factory , no aftermarket, pipes could be a second set , but I wont know till I pull them.

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Carl Stevenson wrote:

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65wagon wrote:

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I don't know Ray , but from what I can see underneath, all the hangers are factory , no aftermarket, pipes could be a second set , but I wont know till I pull them.

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If I remember right the previous owner mentioned that my brother had bent that system that's under there but that's not to say it was single before.

I see him fairly often, I'll ask him next time.

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 please do, and what design wizard would put a single exhaust on a big block anyway , that's in the same line as a two barrel , how ever it ended up there its a goo system except for being two inch, that will be addressed .if I can move the bolts without breaking them. if not I may have to pull things off and do some cleaning at the same time

1975 was the first year for catalytic converters being used in GM cars. the exhaust systems  were already clogged by the converters and use of two for duals was not practical nor any more efficient. 1974 is the last year for what we know as "true" duals on GM cars. Eventually systems evolved with dual mufflers but single converters, the factory Impala system shown above is the only 1975/76 factory system with dual mufflers and tailpipes on a passenger car. Note: the Impala factory "dual" system is 2 1/4" throughout while the factory Pontiac system is 2 1/2" then exiting in 2 1/4" tailpipes. Corvettes always had dual tailpipes then Firebird, Camaro and Grand Prix, Nova a few coming to mind but these were dual mufflers or dual exits from one muffler.

If this 455 Parisienne has no catalytic converter and is a dual exhaust system it is 100% not factory. 

This is an original 1975 style GM Catalytic Converter, these things still cost $500 US today

so imagine GM putting two on a car in 1975...never happened.

ya ill say no to that, im hard pressed to figure out how you get a 21/2 inch pipe on a 2 inch opening, that all will be changed, just finding some 21/2 inch resonators might take some looking, no more noise cant deal with it.