Which of the '73-'80 Chevy's had catylitic converters and which didn't?

[big83chevy]

smog pumps hardly ever seen on anything cept cars, at least int he 48 states other than cali, i cant recall seeing a 73-up with smog pump, i have a 79 big 10 bonanza 350 th350 out here its got a cat on it and is not cali truck

so..

[1FaastC10]

Originally posted by Fast68Chevy
ALL '75-up trucks have them.

WRONG! my '93 C1500 has a C3500 exhaust system from the "converter" forward. all factory GM stuff too, 3" y-pipe and my "converter" is a straight piece of 3" tubing. these are genuine GM parts that i ordered through GMSPO when i was working at the dealership. like Chris said before, it all has to do with GVWR.

[79BIG10]

Originally posted by big83chevy
i have a 79 big 10 bonanza 350 th350 out here its got a cat on it and is not cali truck

You got a pic of it? I've got the same thing here.

[Grim Reaper]

My understanding is that on TRUCKS that 78 was first year for cats in the states Except Cali. I think Cali got them in 75.
On the core suport or the Air cleaner (it was on the air cleaner on my 75 Jimmy) there will be a sticker and if it had Cats it should say CATALIST accross the top and have the Gap and timing info on it as well. That sticker ended up on the core suport from I think 76 up.

[swervin ervin]

Talk about bringing back the dead.

Here's some info from our friend KIILew, thanks again Ken.

----------------------------------------------------------

For 1973 thru 1974, no converters on any models, anywhere.

For 1975 thru 1977, catalytic converters were used on all C/K 10/15 trucks nationwide with GVW's under and up to 6,000 lbs, except 1976 and 1977 C10/15's with the 454 V8. Models with GVW's over 6,000 lbs (i.e. all 1975-77 C10/15's with the F44/Big 10/Heavy Half, all 1976 and 1977 K10/15's and all 1975, 1976, and 1977 C/K 20/25/30/35's) did not use catalytic converters.

For 1978, all C10/15's with GVW's under 6,000 lbs have converters regardless of engine. All other '78 models (i.e. Big 10's/Heavy Halfs, K10's, C/K 20/25/30/35's)had GVW's over 6,000 lbs, and therefore did not use converters. EXCEPTION: For 1978, all California models with GVW's under 8,500 lbs had cats. Therefore, this California exception included ALL and ONLY 10/15/20/25 series vehicles, including Big 10's/Heavy Halfs.

For 1979, Federal laws, like California statutes in '78, raised the GVW threshold. So, all 1979 models, except for C/K 30/35 vehicles, had cats, nationwide.

For 1980 through 1986, the same models as those for '79 used cats. However, a new C6P heavy duty option was offered for C/K 20/25 models which provided an 8,600 lb suspension package. These new, heavier 3/4 tons cleared the 8,500 lb limit, and so did not use converters during this time period, nor did C/K 30/35's.

For 1987 and beyond, all Chevy/GMC fuel injected engines used cats regardless of location or weight class. Only a few 30/35 series chassis cab models offered carbureted 292, 350 and 454 engines, and those were the only models that did not use catalytic converters for 1987 on.

Note: The above applies only to U.S. vehicles. Canadian Chevy/ GMC trucks followed a much simpler story, I think. From what I have seen, no Canadian carbureted Chevy/ GMC C/K/R/V used cats, while all '87 and later fuel injected models did.

[old Rusty C10]

i have a 1976 C 10 custom deluxe with a six cylinder and three on the tree and that bad boy has no cat from what i see most of them until 1977 had no cat ( according to the Walker Exhaust book)

[1FaastC10]

Originally posted by swervin ervin
For 1987 and beyond, all Chevy/GMC fuel injected engines used cats regardless of location or weight class. Only a few 30/35 series chassis cab models offered carbureted 292, 350 and 454 engines, and those were the only models that did not use catalytic converters for 1987 on.

does anyone know where this information came from? it appears to be incorrect. the exhaust for my '93 is for a C309(03) truck (1 ton, SCLB) with the TBI 350. there are definitely no cats involved.

[bpmcgee]

KILLew,

I have a question for you regarding your info on 75-77 trucks.

You state that all had cats except 76-77 454 V8's. Do you mean 75-77? I've got a 75 silverado C10 with a 454, and I have no indication that it ever had cats. Also, it would seem odd to have 75 454s with cats, and then remove them for 76-77.

Thanks,

Brian

[swervin ervin]

Dang, looking back through this very old thread, I see Ken posted exactly what I just did. Must of been where I copied it from.

I'm pretty sure Ken gets his info from GM publications. Not sure, but I think this is it.

As we all know, GM has done some strange things. They never were one to go exactly by a book anyway.

[BillGent]

Why dont you run the VIN number through CARFAX? If It had a different engine in it when built that sight should tell you. It cost like $15 bucks to run it so if you dont want to do that, I have unlimited reports till May 30th or so. Reply or Email with the VIN and I will run it. Lawboybill@yahoo.com (in the subject line..please put CARFAX REPORT so I wont just delete it..I dont read emails from people I dont know.)

[Grim Reaper]

My 75 Jimmy is listed as a 6300lb GVWR. GM side steping and using a loop hole.

I know a bunch of folks with K5's and except cali models, it's rare to see a cat before 78.

[alf4444]

I will add to the confusion. My 78 1/2 ton blazer originally had a 400, does not say "unleaded fuel only" anywhere, had no diagram on radiator support and had no cats. Its GVW is under 6000. It also has no smog pump or anything emmisions related that i can see, unless you count a PCV valve. My buddies 78 truck was identical. Both of these vehicles have resided in emmision counties of Utah for their entire lives. And his passed, hope mine will too

[Bill W]

My 78 Chevy 1/2 ton has a GVW of 6,200 which gets it over the hump of requiring a cat. It also have factory dual exhaust according to the factory sticker in the glove box. Heat riser on the passenger side exhaust and PVC valve. Simple and keeping that way.

Bill

[KIILew]

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

[TIMSPEED]

My 75 C10 SWB MIGHT have originally had a cat...I dunno now though...if you guys say that it will say "CATALYST" on the radiator core support Emissions sticker..then I DIDN'T originally have a cat, cuz my Emissions sticker only says EGR, EFE, and OC Exhaust". But I figured OC Exhaust meant a cat, but maybe it doesn't...

[fastr68]

Originally posted by TIMSPEED
My 75 C10 SWB MIGHT have originally had a cat...I dunno now though...if you guys say that it will say "CATALYST" on the radiator core support Emissions sticker..then I DIDN'T originally have a cat, cuz my Emissions sticker only says EGR, EFE, and OC Exhaust". But I figured OC Exhaust meant a cat, but maybe it doesn't...

check around your fuel cap and on your fuel guage for unleaded fuel warning

i had a 78 big 10 that was 6200lb and it had no cat but im scrapping a 79 big10 and its got a cat and both trucks are 350/th350 12 bolt trucks, i forgot GVW of the 79, ill have to look

if your GVW is over 6,001lbs then it definitely had no cat that year, look on your VIN tag for the GVW

[old Rusty C10]

my 76 c 10 with a 250 and a 3 spd doesnt but the c10 that has the 4.3 has one its a 1986 automatic

[jimfulco]

My 79 Suburban (half-ton 2wd) was a Texas truck. It had a 2ft length of pipe welded in where the cat should have been, a cat instruction sticker on the sun visor, a wallered out restrictor-type fuel filler, & a plate over the EGR port.