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Well, I see this old thread has been opened, and since there are some interesting follow-up posts that seem to contradict my earlier writing, I thought I would write in again.
Mike (Swervin) is right about the source for my information. Most of this knowledge comes from original GM truck data and parts books and other factory literature, along with my own personal observation. Of course, he is also right when he suggests that, after all, GM doesn’t do everything “by the book.” And sometimes neither the books- -nor I- -am correct!
Regarding Brian’s (bpmcgee) note about the ’75 C10 454…
I am wondering what the GVW rating of your particular vehicle is, Brian. According to the 1975 factory literature, the under-6,001 lb application of the 454 does indeed have a catalytic converter. So equipped, the ’75 454 had a 215 horsepower rating. And yes, as odd as it seems, GM was able to recalibrate the under-6,000 lb 454 enough to pass light duty truck smog testing without the cat for 1976 and 1977. Horsepower improved as well, with a jump to 245. This output even exceeded the heavy-duty version of the same engine used in the 6,001-plus GVWR pickup and Suburbans, which was rated at 240 horsepower during ’75 to ’78 model years. When the 454 was again forced to wear the cat in ’78 under-6,001 pound models, the horsepower figure plummeted down to 205.
On the other hand, Brian, if your ’75 C10 has a 6,200 lb GVWR, which was optional at the time, then your 454 won’t have the cat. And if this is not the case, perhaps the ’76 light duty emission 454 recalibration I referred to in the preceding paragraph took place as a running change during the ’75 model year, which is not reflected in the literature I have.
Regarding alf444’s comment about his Blazer and that of his friend…
Everything you wrote is consistent with my understanding of this stuff except for one thing. I wonder what the GVWR plate of your Blazer states. The reason I mention this is because all ’76 thru ’80 K5 Blazer/Jimmy (4wd) models- -and K10/15 pickups- -were cataloged with 6,200 lb GVWR’s. This isn’t to say that I and the GM literature are infallible (I am far from it), but I am very curious!
Finally, regarding Jeremy’s (1FaastC10) retrofit 1993 C3500 exhaust system…
Your post has particularly piqued my interest. I wish I knew what the part numbers of your exhaust components were! I am wondering if the “straight pipe” intermediate exhaust pipe is actually from a 454 1 ton model. The reason I suggest this is that the ¾ and 1 ton 454 models for the ’90 thru ’94 model years placed the catalytic converter BEHIND the muffler. Perhaps the 454 straight pipe used in these applications could be fitted directly to the 350 y-pipe and muffler/tailpipe assemblies. Or perhaps your components are GM “off road” or export pieces. Or, maybe I am just wrong, although I am otherwise pretty confident about the accuracy of my original post. Admittedly, I have yet to acquire a GM original parts book that is specific to the ’93 model year.
Anyway, like I said- -interesting posts!
Ken
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