73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: cwest on March 14, 2014, 10:41:13 am
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I was geeking out and comparing the vin on my 86' K20 350 4X4 to the vin information in a truck catolog. I noticed there's two distinctions for the 350 V8. 'L' just has 350 by it, and 'M' has Heavy Duty 350 by it. Luckily my vin has the 'M' so looks like I've got the cooler of the two! Does anyone know what the differences are in the truck itself that makes it a "Heavy Duty 350"?
Also, just FYI, when I type the truck model into AutoZone's website it says the 'M' is in 73% of models, and the 'L' is in 20%.
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this is a guess but maybe 4 bolt main vs 2 bolt main?
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This is GM's VIN decoder:
http://www.73-87chevytrucks.com/techinfo/73-91VIN/1986truck.pdf
HD is the emissions level not power level even though it made more power.
L - Light Duty Emissions - RPO LS9
M - Heavy Duty Emissions - RPO LT9
http://gmheritagecenter.com/docs/gm-heritage-archive/vehicle-information-kits/Chevrolet-Trucks/1986-Chevrolet-Truck.pdf
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Well that's anti-climatic! I thought it would be something more manly that just emissions:)
I found this yesterday on a 67-72 Chevy Truck site, I thought it might be relevant to what I was asking. Scroll down to the bottom of the page to Cheng's post. Could those be the HD/LD differences? Even though the site is for a different genre of trucks than ours, I think they moved to talking about our years in this thread.
http://67-72chevytrucks.com/vboard/showthread.php?t=510399
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If you look at the link I put last it has the info on the engines.
Chris Lucas
73-87chevytrucks.com
captkaoscustoms.com
squarebody.biz
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Nope just less emission stuff. I would guess what the other thread was talking about would be the rpo code C6P. Which GM offered 2 different 3/4 ton packages. The standard 2500 series had a gvw of 7200 lbs. The heavier 2500 package was designated as a 'C6P' package, which has a GVW of 8600 lbs.
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My computer turns into an ice cube when trying to open larger pdf files.
That's good to know about the C6P package. What's all included with that to bump up the GVWR? I imagine heavier rear leafs and maybe a rear end full floater? Is the frame any beefier?
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Couple of possibilities for why there are two codes/packages.
The mfrs start their model year in the summer, getting the next year's cars in production for Sept/Oct introduction. But the legal standards for pollution measures begin January 1. My dad bought a 1968 Ford Country Squire wagon in late '67, which he got with no pollution controls. Beginning 1/1/68 they started putting on AIR pumps and the like.
One could be California emissions vs. regular emissions. That is unlikely due to the percentage of HD engines.
The last possibility is perhaps most likely. Through 1978, GVW above 6000 pounds required no catalytic converters, so the C-10 had them, but C-20, C-30, K-10, K-20, and K-30 did not. In 1979, this weight limit increased to 8500 pounds. Below that, cats were required, above it, no.
A surprising number of trucks prior to 1979 had 6100 GVW (like my 1978 K-10). After 1979, lots of trucks had GVW of 8600 pounds.
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Cali vs regular was the same motor, just more emissions. I put the engine RPO up for those wanting to find specific info could.
Chris Lucas
73-87chevytrucks.com
captkaoscustoms.com
squarebody.biz
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My '86 Suburban "L" code 350 has two bolt mains.
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Just for information sake the M was 4 bolt main. Not that it was any better than a 2 bolt.
Chris Lucas
73-87chevytrucks.com
captkaoscustoms.com
squarebody.biz
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Thanks for the good info, gents! I'm becoming more knowledgeable about my truck by the post!
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the m code engine is a 4 bolt main and has less emmissions where as the l was a 2 bolt main with the cali emissions i believe if you were to build a aggressive engine you would want the 4 bolt just for the extra insurance
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There is no benefit of a factory 4 bolt over a 2 bolt. If you want strong buy a 2 bolt and install splayed caps. Or just get a 2 bolt.