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Wondering about GVWR

Discussion in 'The Garage' started by RaisedK5, May 1, 2002.

  1. RaisedK5

    RaisedK5 1/2 ton status

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    So , i've had many people look at me funny when i tell them that my truck never came with a cat. And while reading thru the service manual, i finally figured out why, vehicles up to 6200lbs GVWR were required to have cats, and my Blazer is rated at 6300lbs. and has the Heavy Duty 350 and is supposed to fall into the Heavy Duty classification for emissions, according to the sticker in the engine bay, So i was wondering what the GVWR is for other years, Did they just up the GVWR to get around emissions or is it really that high? So what's the GVWR on your trucks and what do you think???
     
  2. m j

    m j 1/2 ton status

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    my 77 1/2 ton was a regular fuel vehicle therefore no cats
     
  3. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I think 78 was the first year for cats...

    Rene
     
  4. Twiz

    Twiz 1/2 ton status

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    Just to confuse you further.....

    At some time (I'm guessing around 81/82, when the VIN numbers became uniform) I think they also changed the GVW rating system.

    8600 and up is now the heavy-duty weight rating. It seems to me that the older models with, more-or-less, the same equipment had a lighter GVW ratings, some where in the 6s.
     
  5. gtkustoms

    gtkustoms 1/2 ton status

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    my 80 burb doesn't have them but its a 3/4t dont know the gvwr off the top of my head.
     
  6. gokartergo

    gokartergo 3/4 ton status Staff Member Moderator

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    My 77 is that way..Stock with No cat..But my dads 77 vette as cats..My brother is a smog tech and it went by GVWR in those years...Dan
     
  7. m j

    m j 1/2 ton status

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    hmm californian EH.
    think maybe you guys got stuck with differing smog rules back then as well?
     
  8. HarryH3

    HarryH3 1 ton status Author

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    In the mid-70's the feds came up with the rule about catalytic converters. The first time around, any vehicle with a GVWR over 6,000 lbs would be exempt. Ford quickly upped the GVWR on the F-100 to something like 6,050 lbs. and badged it the F-150. GM did something similar with their half ton trucks and called them "Heavy Half". Over the years, the GVWR limit kept creeping upward. Once it got high enough that adding another leaf to a spring pack wouldn't get a vehicle over the limit any longer, they got the cat. /forums/images/icons/wink.gif
     
  9. RaisedK5

    RaisedK5 1/2 ton status

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    Ok that makes sense, cause i gave my stock packs to one of the other guys with an earlier blazer and he said they were at least a leaf or two thicker. I see, so they were just trying to beat the system.
     
  10. barbastard

    barbastard 1/2 ton status

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    I live in Northern CA and I bought my 77 K5 from my dad last year and he told me it was "Smog exempt" because of the weight (listed at 6360), and I never understood how that worked. Especially since every 2 years I still have to go get it "smogged", but even on the smog cert. it states "smog exempt". NOW IT ALL MAKES SENSE!!! I'll find out this August how well the smog technicians buy off on that one....my dad had a hard time finding techs that had heard of this or believed him.
     
  11. gokartergo

    gokartergo 3/4 ton status Staff Member Moderator

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    My brother is a smog tech. That is how I found out about it..But the weight is above 6100 pds for 77.. And the gvwr on a 77 is 6300...Dan
     
  12. MudbogAD

    MudbogAD 1/2 ton status

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    My GVWR is 6200 on my 79 Jimmy. It doesn't have cats now and I don't think they came stock on mine either.
     

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