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  1. #1
    Member 1989 406's Avatar
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    Default Catalytic converter question.

    On a 3 inch set up, how much of a gain or not is to be seen by removing them? I know it I illegal.

    What are you guys doing with your convertors?

    Are they a major restriction on a non aspirated motor?

    Are the high flow ones any good?

    Thanks.

  2. #2
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    Member G Winter's Avatar
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    1990 red convert 6 sp

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    If you have dual 3 in up front the single 3 in in the middle will be the bottle neck.
    Dual 3 in is a lot of volume.


    Glenn

  3. #3
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    I honestly don;t believe that late model cats make one single bit of difference on a street car regardless of the mods to the engine. There is no "low pressure area" behind the car to make a difference in the exhaust flow rate....THATS got more to do with the exhaust flow than a cat does these days.
    There is no pressure build up inside from a cat. Hell, the system is considered to be plugged if it builds more than 2-3 psi back pressure. If 3 psi is gonna keep me from enjoying the HP & torque that i KNOW to be there now WITH a cat, then I got other things to be worried about...like a more aerodynamic front end....less drag at the tail...all sorts of microscopic enhancements to be done to add 0.02 in the quarter mile or get another 2 mph top end...( on a DD street car) yeah right...

    The cats just are'nt that important. You don;t want a free-flow system anyway. Its been proven time and time again that low end power suffers when the exhaust gets too big or the flow gets too easy.
    Maybe back in 1988 cats sucked but todays cats flow gas like they were hollow. They HAVE to...as much as the EPA likes to tie the hands of the auto makers, they also have to accept the science and understand that exhaust that does not flow outward severly restricts an engines ability to generate the most possible power from every gallon of fuel, thus creating more pollutants. Cats have little or no effect on street engines.
    If you DO have an antique cat then replace it. I would not buy a car that had no cats...a huge headache for a buyer if that day ever comes. I would not count on never having to do a smog either....its gonna happen to everybody sooner or later. States that do not require it today, will loose federal funding for their hiway projects and other infrastructure until they go along with the EPA guidelines. They have ways of making state gov cooperate.....($$$$$$$$$$$$$$)

    Not worth the hassle to cut 'em out and then have to retune for whats gonna be a temporary system.

  4. #4
    Member aklim's Avatar
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    I put a gutted cat tried it. When the noise was unbearable, I put a straight pipe. It was still a little too much. Put a Random Tech high flow cat and it is tolerable.
    Holley Stealth Ram, 42# injectors, AFR 190 heads, 1.6 intake RR and 1.5 exhaust RR, 230/236 - 110 lobe sep, 108 intake centerline (2 deg. advanced), TPIS Long Tube Headers, Random Tech Cat, Borla exhaust, Rossler Trans, HiTech Motorsport tuned ECM.

  5. #5
    Member aklim's Avatar
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    Quote Originally Posted by G Winter View Post
    If you have dual 3 in up front the single 3 in in the middle will be the bottle neck.
    Dual 3 in is a lot of volume.


    Glenn
    If the exhaust gas volume is much larger, maybe. However, if there is no need, there is no need. The major question is this. How much flow are you getting that it justifies a dual 3 inch system? In an all out drag race, yes. On a DD, I think not
    Holley Stealth Ram, 42# injectors, AFR 190 heads, 1.6 intake RR and 1.5 exhaust RR, 230/236 - 110 lobe sep, 108 intake centerline (2 deg. advanced), TPIS Long Tube Headers, Random Tech Cat, Borla exhaust, Rossler Trans, HiTech Motorsport tuned ECM.

  6. #6
    Member 1989 406's Avatar
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    Default

    Thanks guys. The po had a straight 3 inch dual system going out to 2 1/2 mufflers, original mufflers were 3 inch but it was too loud of a muffler for him so he had it changed.

    I am guessing I need two 3 inch cats for the system.

    Any good names out the with 3 inch cats that flow good?

  7. #7
    Member aklim's Avatar
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    Quote Originally Posted by 1989 406 View Post
    Thanks guys. The po had a straight 3 inch dual system going out to 2 1/2 mufflers, original mufflers were 3 inch but it was too loud of a muffler for him so he had it changed.

    I am guessing I need two 3 inch cats for the system.

    Any good names out the with 3 inch cats that flow good?
    IF it were me, I'd get a good set of headers, TPIS comes to mind, Random Technology Cat and a Borla exhaust. That is the setup I am running. 2 banks dump into a Y pipe and a cat to the back where it can dump out to 2 exhaust mufflers. Personally, on my Firebird, I had it dump into 1 high flowing muffler. I don't remember the article I read years ago but unless there is an X pipe, you lose scavenging at low rpm. At WOT, nobody cared and while it was great for drag cars that were going WOT, it didn't make a good DD. However, monkey see, monkey do and everybody wanted duals running out from each bank even if you lose clearance because the rice crowd expected it.
    Holley Stealth Ram, 42# injectors, AFR 190 heads, 1.6 intake RR and 1.5 exhaust RR, 230/236 - 110 lobe sep, 108 intake centerline (2 deg. advanced), TPIS Long Tube Headers, Random Tech Cat, Borla exhaust, Rossler Trans, HiTech Motorsport tuned ECM.

  8. #8
    hotmtrsports's Avatar
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    If you or anyone could use two 2 1/2" Cats. I have these that I bought new, still in boxes and never used from Jegs...

    Dynatech 779-40025 Dynatech PowerCat Catalytic Converters

    I paid 169.99 each + shipping for about $360.00

    I'd sell them for $250.00 with free shipping in the USA.

    (didn't mean to hyjack, just thought this would help)

    Thanks,

    Chuck
    Doesn't everybody have a 4 post lift in their garage?

    Corvette Museum Founding & Lifetime Member #4125

    www.corvetterepairsofmaine.com

  9. #9
    Member 1989 406's Avatar
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    Default

    Thanks guys,

    Money is the key factor here so I will have to figure out the least expensive way around it. If I could find two 3" converters and get them on, that may be the best way to go. I have to see if anyone makes them. I thought I had seen some online before.

  10. #10
    hotmtrsports's Avatar
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    3" High Flow Converters...

    Here ya go:

    Dynatech 779-40030 Dynatech PowerCat Catalytic Converters



    Chuck M
    Doesn't everybody have a 4 post lift in their garage?

    Corvette Museum Founding & Lifetime Member #4125

    www.corvetterepairsofmaine.com

  11. #11
    Member 1989 406's Avatar
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    Default

    Thanks for the link.

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