57 66R resonator cutting according to service bulletin

[57Century]

I have a set of NOS resonators that I'm installing on my Century.

According to the service bulletin the 2" pipe should be cut and replaced by a 1 3/4"

Any idea or suggestions why that should be done?

[lancemb]

Not sure on this, but the only 2 possibilities I can think of is possible contact/interference with the baffle when it vibrates, or to minimize blowback/enhance exiting of exhaust through the baffle.  I've used 2" pipes without issue; I personally would not bother. 

[lancemb]

One more thing, those NOS baffles will rust quickly (at least on surface) resulting in rusty water blowing onto your bumper openings.  You can paint them with silver POR-15 to keep them from rusting, and this will also make the exhaust residue wipe right off.  You'll still get some on your bumper on the edge of openings but at least it won't be rusty condensation.

[57Century]

On 11/27/2021 at 2:29 AM, lancemb said:

Not sure on this, but the only 2 possibilities I can think of is possible contact/interference with the baffle when it vibrates, or to minimize blowback/enhance exiting of exhaust through the baffle.  I've used 2" pipes without issue; I personally would not bother. 

Super. I will keep as is and if it becomes an issue I can always change it.

 

On 11/27/2021 at 2:32 AM, lancemb said:

One more thing, those NOS baffles will rust quickly (at least on surface) resulting in rusty water blowing onto your bumper openings.  You can paint them with silver POR-15 to keep them from rusting, and this will also make the exhaust residue wipe right off.  You'll still get some on your bumper on the edge of openings but at least it won't be rusty condensation.

That is a very good input. I will do that.

Thanks.

[buick man]

Kasper ... Here is the story behind the size change instructions. The resonators were installed from the factory on dual exhaust equipped jobs only.  The factory early to mid run jobs all had 2-inch I.D. exhaust systems all the way from front to back.  Then apparently some customer exhaust noise complaints begun what with the combination of the higher lift cam and higher compression the Century, Super and Roadmasters 364 came with and produced too much idle lump and launch exhaust noise or so in the subjective opinion of a good amount of new car owners.  So to appease those complaints the factory sent out a bulletin advising that a replacement system would now be produced with 1-3/4 inch I.D.end pipes in an attempt to quiet the exhaust output and thus the factory instruction sheet you have posted was made available along with a new 1-3/4 I.D. tail end piece.  

 

This was done in an attempt to " quiet " the claimed exhaust noise and complaints until the factory could produce the entire exhaust system in 1-3/4 inch I.D. from front muffler to resonator to end tail pipe.   For 1958 jobs all the systems front to back were 1-3/4 I.D. On a side note, one may if real lucky still find the early job NOS factory front mufflers ( A dual paired muffler )  that are in the original 2-inch I.D. configuration along with the rear resonators but are by this time very rare and I have only seen perhaps 2 or 3 available NOS factory front mufflers ( 2-inch ) for sale in perhaps 12 years.

The 2-inch I. D. resonators however are still popping up from time to time as NOS aftermarket units  now and then but predominately as 1-3/4 I.D. units.