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  1. #1

    Default 1991 454 exhuast questions

    Th 91 is the last year of that body style. i have been informed that a 3" single exhaust is the best way to go here. I have a 3" system and they are trying to get me to go new pipe because the stock has "bad bends" that are power robbing. I wasn't born tyesterday. I asked about putting in a full flow muff, flowmaster or magnaflow, and the muff is a 3" double offset. No one has a listed muff for the suburban, I think that it is a weird setup with the muffler before the cat. One guy said that was to keep from burning out the cat, another said that I would hear a "whistle" unless I put the muff after the cat.

    I can't get an honest answer. my friend's dually singlecab 1 ton has duals and when the flowmasters were on it they had a resonance that pounded the ear drums at highway speed. i do not want that.

    Does anyone have this combo? What did you do and is it unbearable? I want to run the biggest full flow that I can find for a realistic price.

  2. #2


    Well they were telling the truth about the power robbing bends, just exagerating it a little, if you've got 3" from manifold to exit you should be good to go. Actually if the engine is relatively stock 3" might be a little to big.
    The price for the specific muffler they want to install must be a little higher, you can use any muffler that fits, mufflers are universal, provided they fit your exhaust pipe and space under the truck. Maybe time to go see a different shop.
    Flowmasters are a little louder than other mufflers, A Magnaflow or Gibson might be a little quieter. I have a full dual system on my 97 7.4 and it's a little loud at take off and when backing down the throttle but during steady highway cruise its ok. Cat and muffler placement on the Suburban was due to space available and heat build up, remember the factory muffler was huge and couldnt fit in very many spots under the truck, this caused some minor sensor issues when they first started putting the muffler first, the secondary exhaust sensor on some models was getting fouled and burning out because the cat wasnt getting hot enough to properly burn off all the waste gasses.

  3. #3


    Is there any truth to a "whistle" sound after installing a full flow muffler in stock position behind the cat?

    Edit: My muffler is between the engine and cat. I said it backwards. Is there a "whistle" from the exhaust if there is a full flow muffler before the cat? Some BB chev trucks have the cat downstream of the muffler. I had a shhop refuse to work on it because they claimed that it was not legal, and could not be stock! I won't be doing business with this garage, they obvoiusly did not know.
    Last edited by route66paul; 07-27-2008 at 11:53 PM.

  4. #4


    never heard any whistling.
    Two Suburbans before this one I had a 91 B/B with the cat bfr the muffler. Couldnt tell ya how many GM trucks I've seen with that configuration exhaust and I've never heard of a problem with them either.

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