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Dual exhaust: How and Can I legally?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by txbartman, Oct 19, 2001.

  1. txbartman

    txbartman 1/2 ton status

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    Okay, here's the deal...

    This Spring, I am putting in a new 350 GM crate. I currently have a 305 using a Y-pipe, single original factory cat with single-in, single-out into a cheap muffler single-in, dual-out that then exists the side behind the driver's side tire.

    When I do the new 350, I would like to do dual exhaust exiting the rear or at least one on each side. I was originally planning on true duals... headers...cat...muffler...tips for each side. I have to have the cats since I need to remain street legal. If I had a single cat from the factory, can I legally go with dual cats? Is it even worth the expense? Would I be better to go with headers...a new Y-pipe and single cat (with larger input/output than factory? If I go that route, should I split coming out of the cat and go through dual mufflers and exit?

    The emgine I put in will not be performance, but a good, solid, reliable GM 350. I am planning on using TES headers. I want good sounding exhaust that will also not hinder any HP I may be able to squeak out of the engine. I need to keep legal and I don't want to break the bank. I don't mind spending money to do it right the first time, but I also don't want to spend $1,000 on my exhaust system.

    Who can help me?

    Brian
    Check out <a target="_blank" href=http://tx85gmcguy.alloffroad.com>My Jimmy</a> with all her projects!
     
  2. ftn96

    ftn96 1/2 ton status

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    NOPE!!! If it didn't come from the factory with true duals, then it is ILLEGAL to put true duals on it.

    Surgeon General's Warning:
    Viagra and steroids may be harmful to your spouse![​IMG]
    <a target="_blank" href=http://www.nashvillek5.freeservers.com>www.nashvillek5.freeservers.com</a>
     
  3. txbartman

    txbartman 1/2 ton status

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    How do they know? Were there no true duals from the factory in 85? Do they lookup based on the VIN and know what came with it? I certainly can't think they are that advanced. I know the VIN indicates the engine, but exhaust?

    Brian
    Check out <a target="_blank" href=http://tx85gmcguy.alloffroad.com>My Jimmy</a> with all her projects!
     
  4. Derf00

    Derf00 1/2 ton status

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    Yes they do know. If your engine is not highly modified the expenses involved in adding ture duals is not worth any hp gains you might get. In fact, there have been a few articles and tests that show a single exhaust, cat, etc will produce just as much, if not more hp than a dual set-up on a stock to somewhat modified 350.

    Derf00

    "A WISE MONKEY NEVER MONKEYS WITH ANOTHER MONKEY'S MONKEY."
     
  5. Jersey

    Jersey 1/2 ton status

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    I guess it would really depend on what you're going to do with the 350 down the road. You want some back pressure but you also want the 350 to breathe. My (basically stock) 350 with the stock manifold running single 3" the whole way with a flowmaster cat and muffler seems to be just right for my K5 and the sound is nice. not to soft, not annoying on longer rides. If i were to do it again though, i would probably run true 3" duals into a pair of the same type of cats and muffs. My '77 CJ had that setup and it sounded and performed real nice with the built 304 in her. Probably a little too loud for me now (getting old &lt;img src="http://coloradok5.com/forums/images/icons/wink.gif"&gt;) but it turned heads and liked to run. BTW - Sure glad i graduated from the CJ to a real truck &lt;img src="http://coloradok5.com/forums/images/icons/smile.gif"&gt; I wouldn't go from two up front to one cat back to splitting into 2 again. defeats the purpose IMO. Haven't had much experience with headers but i'm sure someone can shed some light. Hope my rambling (lots o coffee) helps. And, find a buddy who knows a buddy that has a garage that does inspections.

    - Jersey

    '91K5 - 350, 700R4, NP241, FlowMasters, 33's
    &lt;a target="_blank" href=http://pages.zdnet.com/len1313/blazer&gt;[/b]PICS[/b]&lt;/a&gt;
     
  6. BowtieBlazer

    BowtieBlazer 1/2 ton status

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    I'm going single pipe soon versus the duals. Here is how you do it! The stock exhaust is 2 ½" in some places and 3" in others. Have the muffler place cut the stock pipe just before the reducer to 2 ½" and insert that new cat. If they have to, cut the exhaust back to where the two pipes join from the heads. It is 3" at that point. Also, run 3" pipe into the muffler from the cat. This was the biggest improvement that you will notice, both in HP and torque with a single 3"pipe.


    What? You think the hole is too deep? Lemme see...
    1985 GMC C-10 Shortbed
    1984 Chevy K-5 Blazer
     
  7. ironmikek5

    ironmikek5 1/2 ton status

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    I just got a kit for the stock exhaust, one pipe to muffler, dual tails. It looks like the tails are basically the same, same bends, one is longer. On the stock exhaust, do the dual pipes both exit on the drivers side?

    <font color=red>I will not tolerate intolerance </font color=red>[​IMG]
     
  8. Stoopalini

    Stoopalini 1/2 ton status

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    When I went to get my truck inspected, I was told '84 and after need cats. '83 and before, do not (this is in TX).

    I have true dual exhaust on my truck with no cats (mines an '84). The engine, tranni, and both axles have been replaced and highly modified from the factory. The inspection station told me I would have to install cats in order to get the truck past inspection.

    I don't see how having dual exhaust could cause you to fail inspection if you have cats on there and are within the emmision limits?? (for the states that require it)

    I would go with true dual if I were you. The only thing I would change on my existing setup, would be a pipe to connect the two sides together to eliminate the resonation you get from doing 60mph down the highway.

    Thomas.

    -- '84 1-Ton Blazer --
    When the goin' gets tough,
    the tough go 1-Ton [​IMG]
     
  9. I don't know about Texas, but here in Oklahoma, it is legal to run dual exhaust with dual cats, even if it didn't come from the factory that way. Not all states are like this, however, so you need to check with an inspection station or the DOT to find out. If I were a betting man, I would say Texas law and Oklahoma law are the same in this aspect, because I know they sell a lot of trucks here called the "Oklahoma/Texas" package.

    God has a hard on for Marines, because we keep Heaven chock full of fresh souls!
     
  10. ftn96

    ftn96 1/2 ton status

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    I agree stoop. But Even with cats on both sides, they still said NO, but Im here in TN. They do a visual on the cats and the sniff check.

    Surgeon General's Warning:
    Viagra and steroids may be harmful to your spouse![​IMG]
    <a target="_blank" href=http://www.nashvillek5.freeservers.com>www.nashvillek5.freeservers.com</a>
     
  11. Stoopalini

    Stoopalini 1/2 ton status

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    Humm, sometimes it's all in the shop you bring it to too [​IMG].
    Heck, I've payed $30 for an inspection before! Of course, this was years ago, and also back in RI.

    Maybe TN has some sort of law about having the exhaust in the stock config. But it doesn't really make sense?
    So what do you do if you get a car with a stock V6 (like a Cutlass) and swap a V8 into it? You're not allowed to run dual exhaust?? Wierd ............

    Thomas.

    -- '84 1-Ton Blazer --
    When the goin' gets tough,
    the tough go 1-Ton [​IMG]
     
  12. txbartman

    txbartman 1/2 ton status

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    Yes, the both exit just behind the rear wheel on the driver's side. On in front of the other. That is why your pipes are bent the way they are.

    Brian
    Check out <a target="_blank" href=http://tx85gmcguy.alloffroad.com>My Jimmy</a> with all her projects!
     
  13. HarryH3

    HarryH3 1 ton status Author

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    It's a federal law that exhaust system modifications cannot change the size, location or number of catalytic converters. Some states just overlook it. Others will send you back to the muffler shop. This is the major reason that so many cat-back exhaust systems are available these days. It's also why headers that dump into a single pipe are widely available.

    <font color=black>HarryH3 - '75 K5</font color=black>
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  14. TXBIGFISH

    TXBIGFISH 1/2 ton status

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    First what county are you in? If you are not in Dallas County, you will not have to meet as strict emission standards, I have an address in Emory and have the registration sent there, I have no cats and a true dual and have never had a problem. I know of very few inspection stations here in the DFW area that do a visual inspecion under the body, but some do under the hood, but they all do sniff tests in Dallas County. Ask around, some stations are more lax than others. Occasionally if you go to the right place, if it drives in undrer it's own power it passes. If in doubt call or go by a muffler shop and ask, or inspection station, I'm sure they can answer any questions, and ask more than one. I am in the inspection business, building though, and a lot depends on the person doing the inspection and what they feel is inportant, and most of all how knowledgeable they are. Some snot nosed kid that just started do inspections might miss a lot of stuff someone with a lot of experience will catch.
    Hope this helps.

    &lt;*)))&gt;&lt;

    81" GMC Jimmy.............stock for now!
    I see a 6 inch lift in the near future!
     
  15. MudFrog

    MudFrog 1/2 ton status

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    My dad sells exhaust systems for a living, Flowmaster, Magnaflow etc.. He told me that it is illegal in the US period to run dual cats if the vehicle did not come that way. Now I'm not saying some of ya'll are wrong, it could very well be that he is wrong, but all I'm saying is since this is what my dad has dealt with for 20 some years I'm gonna stick to what he says. I also wanted to run headers on my truck but he said the only way to keep it legal would be run headers to 1 cat and back out again. Thats why I'm running single in dual out.

    89 K5 Silverado
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  16. Hossbaby50

    Hossbaby50 3/4 ton status

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    I run true dual exhaust in Phoenix AZ. It is one of the strictest emissons cities in the US and they didn't say jack last time I had it emissions tested. I do have dual cats. I was told that my exhaust is illegal by the shop that put it on, but nobody has said anything yet. If you are really worried about the legality then just get the 3" single exhaust done with high flow cats and a good muffler.
     
  17. dyeager535

    dyeager535 1 ton status Premium Member

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    Your dad is correct. Its federal law, that supercedes all local and state laws. You can NOT modify the amount of catalytic converters the vehicle came with. One exception is the entire engine out of a newer vehicle, from smog pump block to exhaust. (such as a 90's Camaro with true duals) You are getting into SERIOUS gray area with that though, and as most things emissions, every person you talk to from the government is going to give you different answers. Fact is, federal law, you can NOT change the number of cat converter on a vehicle. Does not matter if its for racing or not. I'm not saying that is correct (because if you can get lower emissions with dual cats, what kinda idiots are running this show?) I'm just saying thats the way it is.

    Diesel trucks exit one pipe on both sides for true duals, later (81-91 or so) gas "duals" are just dual tips, and they exit both out one side.

    personally, go with 50 state emissions legal headers, and a single 3" pipe/converter combo. Save yourself some serious problems potentially, and still get good performance.

    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>www.dorianyeager.com/index2.html</a>
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  18. ChevyCaGal

    ChevyCaGal 3/4 ton status

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    Check to see the law about the pipes exiting from the back straight out if you are considering that. I have found that some states do not permit this with a back window that rolls down due to the fumes it sucks in....

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  19. 82Jimmy

    82Jimmy 1/2 ton status

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    I have an 82 Jimmy that came with factory duels if that helps at all. I say just do it, unless you live in a big city. My friend has a 83 GMC Pickup that had a Y and what he did was put 2 little bitty glass packs on and put some "Fake" cadallic converters on and welded them over the one of the Glass packs, needless to say it is the loudest thing i have ever heard and it sounds like a jet when he comes off the accelerator. This may not be what your asking, but just giving what little advice i know. I ran NEW duels straight out the back and had to pay to get them bent at a 45 NOT a 90. They come out at the cornor of my bumper now, don't run them out the back or the fumes when you roll your back window down will be terrible. Very VERY VERY bad, and i seemed to "space out" when i did roll my window down. hehe

    ..........and one time at band camp.........
     
  20. blah, bah.....

    go to a local INDIVIDUAL OWNED shop, not one of those 'sticker stop' places... it isin't difficult to-

    A: find a shop that will run a smog test without worrying about how may catcons you have versus how many came from the factory... who cares????? the EPA or CARB can make all the idiotic mandates they want- if you get a catcon per side, and can pass smog, youre doing fine!! you live in tarrant county? i'm down here in houston ( harris county, home of the worst air in the US) and most of the individually owned shops will just stuff a sniffer in whatever pipe and go... those guys dont give a crap...

    B: find a shop that will pass your truck, no matter what. i was having my wife's oil changed ( no, i don't change oil- too hard to dispose of to warrant the $7 saved ). and was talking to the owner of the shop. i was asking how much some downturns would be since i had to cut my exhaust over the rear axle to get it out of my 70 and into my 83... he said what stoop said about cats and, ' hell there's lotsa ways to make 'em pass smog, if you slip ol' buford there a 50, i'm sure he'd pass it.... '

    i dont know how it is in (insert your state other than texas here) but since you're in texas, i wouldn't worry. lemme talk to some of my boys up there and see if i can suggest a shop in particular....

    PS any of you texas boys heard of anderson, texas?? the lady at the inspection place there used to just take my 15, copy down the odometer number, and put on the sticker...

    greg
     

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