Hello, I am new to this site and just purchased an 83 High Sierra 2500 4x4 700r4- I am reading about the different GVR and engine codes, can anyone edjucate me on what I have and where to look for more information on this great truck? Thanks and will post pics with full story soon.

Look at the 8th digit of your VIN code. A "C" indicates a light duty application, a "J" indicates heavy duty. C code 6.2 diesels have an emissions doohickey right in the middle of the intake manifold. Many people remove this or replace the entire manifold with a J code model for slightly better performance. I believe the injection pumps are calibrated differently as well.

Mine

Mine is a J code!!! hoora

ok what if it is not the stock motor? I just put new motor in my truck that I pulled out of another. but the donor has already gone to scrap.

Take the lid off of the air filter and look to see if there is an "emissions doohickey right in the middle of the intake manifold".:lol:

Is that the only difference? a little bit more power with J code and a doohickey under the aircleaner with C code?

the doohickey restricts some airflow and restricts a bit of exhaust. hot exhaust in intake also loses some power. changing manifolds to a j caode is pretty much the difference. the j code pump does add a little bit of power

i was under the impression that the j codes had slightly larger valves in the heads as well. Is this correct?

i was under the impression that the j codes had slightly larger valves in the heads as well. Is this correct?
in the first few years, yes. then for most years no. they gave up on it as the heads were cracking to much

What years were the larger valves in? When was the 6.2 first put in trucks? Are there any other good reference websites to find out original GMC 6.2 info/options? every time I do a search links for this website come up!!! Thanks again for all the great information!

This website keeps coming up because EVERYONE knows that these guys are the gurus...(I bow to them regularly):lol:....As far as 6.2's go...82 was the first year. The valve size differences...I don't know. Diaric should be able to shed light on that.

you give me too much credit, i'm just going by what i've read. I think the big valves went somewhere around 84. i've had a few people offer me one, get that, 1. the other was always cracked real bad

you give me too much credit, i'm just going by what i've read. I think the big valves went somewhere around 84. i've had a few people offer me one, get that, 1. the other was always cracked real bad
See how ya are....try to put a man on a pedestal and he crawls under it:lol:

How can I tell the year of my motor? I am pretty sure it is original 83... Wondering if it it original or maybe I should plan on having a set of small valvle heads on hand just in case? Or what do you think of a build up or I was even going to look for a military 6.2, I have found many for surplus purchase, but I would most likely go through it in my spare time just to have it on hand. Sounds like a lot to undertake, but I will need this truck to be back on the road ASAP incase of some tyoe of failure. I have never rebuilt a diesel, but many gassers. You guys are as knowledgeable as my old neighbor Mr. Goodwrench!

There is a stamp on the block under the alternator. "D" is 1985 --- there's been posted a list a few days ago here ...