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Gas Mileage and Hi-Flow Cats.

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by okie k5, Mar 29, 2005.

  1. okie k5

    okie k5 Registered Member

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    Hey everyone thanks for reading. I was wondering what everyone thought about Hi-Flow Catalytic Converters. I am going to get a new muffler and tail-pipe, the old rusted out, and so I was planning on getting flowmaster. I have had them before and I like everything about them. I was considering getting a new cat, have to have one for emmissions, but I did not know if anyone had experience with the "high performance" catalytic converters. I am really interested in gas mileage, but who doesn't like horsepower right? I have heard that hi-flow cats are not worth the time or money because a cat is a cat is a cat. Anyone have any ideas? If you think they are worth it please state a good brand/model. Thanks.
     
  2. jarheadk5

    jarheadk5 1/2 ton status

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    Not all cats are made alike. The way the actual catalytic element is formed has a direct effect on the flow of exhaust gases through it. Here's a good link from a performance cat mfgr.:
    High-flow cat tech
    IMO, if you have to run one, a quality high-flow cat (like one from Random Tech.) is worth the money. There's been so many dyno tests over the years that they can't all be wrong...
    BTW, replacing a trashed stock-type exhaust system with a free-flowing exhaust system is capable of bringing your fuel mileage up, IF you continue to drive the same way. But that never happened to me; I enjoyed the new-found power under my right foot, and took advantage of it, so my mileage went down. But my smile got a lot bigger... :D :D
     
  3. Thunder

    Thunder 3/4 ton status

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    The stock Cat in K5s doesn't flow real well espically when they get old.
    I would definatly get a new high flow cat if you are putting on performance exhaust.. Dont expect big gains in gas milage with performance exhaust. maby 1 to 2 MPG
    Catco cats are a pretty good convertor. Summit has them for 70-80$
     
  4. joefl

    joefl 1/2 ton status

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    i was wondering the same thing about high flow cats.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    You've got an O2 sensor, you could always do the GM test for backpressure, which is to tap into the exhaust with a pressure gauge and make sure it isn't excessive.

    I *think* anything over 4PSI GM determines is excessive.

    That number probably varies between applications, I think that number came from the Camaro service manual for 1988.

    My own opinion about high flow converters is that the testing is always done with a new high flow versus an X year old stock one. An old one is of course much more likely to have flow restriction due to breakage, etc., so the testing has been skewed IMO.
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    You've got an O2 sensor, you could always do the GM test for backpressure, which is to tap into the exhaust with a pressure gauge and make sure it isn't excessive.

    I *think* anything over 4PSI GM determines is excessive.

    That number probably varies between applications, I think that number came from the Camaro service manual for 1988.

    My own opinion about high flow converters is that the testing is always done with a new high flow versus an X year old stock one. An old one is of course much more likely to have flow restriction due to breakage, etc., so the testing has been skewed IMO.

    Not that a stock cat can't be "worn out", just that a lot of the claims are made to sell you stuff. Imagine that. :)
     

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