RPO Code Clues

[GASoline71]

CHX = 1977 350, 4bbl, 170hp

Gary

['68OrangeSunshine]

V = Flint Mich. [Line 2 maybe?]
03 = March
27 = 27th
CHX = ? not listed in the old LMC catalog I'm using. They are not the last word however.
Waitresses used to use the letters ''CHX'' as shorthand for chicken, but that has no relation here. Just kidding.
Mainstream 327 numbers are YS, YR, YD, YJ, YH, YB, YM, YK, YV etc.

Google ''engine decoders'' under <<67-72chevytrucks.com>> in the black box at the top of the page above subscribers/calender/search. It will turn up several choices.

My '68 C/10 had a 292 with the letters "XAE" when I bought it in 1973. I have never been able to find that suffix anywhere.

[68 TT]

Glad you and the truck made it home safe and in one piece. It is equipped the same as my 68 C20 suspension wise all the way down to the helper springs and 7500 pound GVW. Notice they have 6000 on the bedside? I bet they had it registered at a lower GVW to save on registration fees.

You need to remember these trucks are over 50 years old and have had a whole lot of time for people to monkey around with the engines and parts on them. I have found some pretty odd things changed out on low mileage original vehicles so you need to take everything you see and were told about the truck with a grain or two of skepticism until you can verify it yourself. Parts get changed out with whatever is on hand not necessarily with what is correct. Differentials and transmissions are the prime culprits in non-originality that I come across as they were less expensive to change out than to rebuild for much of the life of the trucks and in many cases still are.

The engine is a prime example of things that get monkeyed with. My 67 Suburban has 90k original miles and had been parked since 1979 and sat under a pine tree for more than 30 years before I purchased it. The engine looked all original at first glance and the owners son who was selling it thought it was the original engine as well. Upon tear down I found the original 327 had been replaced with a 71 Chevelle ID pad coded 350 rebuilt short block and 4-bbl valve size cylinder heads but had the correct to the Suburban 2-bbl 327 intake and all the original accessories reinstalled. It must have been replaced very early on as the engine was covered in crud to a similar degree as the rest of the engine compartment and chassis.

In your case just because the block code says the engine is a 1977 vintage 350 doesn't mean the internal parts or anything from the cylinder heads and intake on out are from that engine. A large journal 327 crank will drop right into a 68-up vintage two-piece rear main seal 350 block making it a 327 so don't discount having a 327 entirely just yet. I would take that with a bit of skepticism though as I have heard many people falsely claim their anemic low HP smog era 350 was a 327 to make it sound better to others

The only way to know for sure is to tear it down and measure the piston travel in the bore or ID the crank casting number.

The casting numbers under the valve covers will let you know if the heads match the short block or if they are from another engine entirely. On the back of the block on top of the bell housing mounting flange will be a casting date code in addition to the block casting number. The cylinder heads will be fairly close to this date if they are correct to the engine. Usually within a month but sometimes a little more.

The seat you have is from an 88-97 body style GM truck. They fit pretty well in our cabs but the seat back angle is a little off so you can't get it back as far as you may want and it is a little tall. Good for short people but not so much for taller people like me. I am in the process of a little seat mount surgery so the seat back angle more closely matches the fuel tank angle and lowering it as much as I need right now for one of my projects. Not sure how it will do as far as seat bottom tilt. I may have to compromise somewhere in the middle to get a seat bottom angle I like with the seat as far back and low as I can get it where the seat back latch locking mechanism still functions. We will see.

[HomeMadeSin]

Yes, given the variations so far I fully understand what you are saying. Although I've been thinking about the path forward for some time, now that I have the truck its kicked up several notches.

Without question, a front disc upgrade is happening. I haven't found a front end donor locally so am looking at the disc kits. No way in hell I'm driving with drums up front.

I'm leaning toward staying with a bench seat, but don't want a hokey frame/support. There appears to be a reasonable chance of finding a decent, period correct bench.

The real question is the motor and transmission. I want to stay with a manual gearbox but the SM420 might drain my enthusiasm at highway speeds (it is a 4.56 rear). Besides, it would eliminate many potential thieves that don't know how to shift...

Given the expense of rebuilding what appears to be a late 70's crate motor, I think buying a modern Vortec-based system would be more ideal. That's the course I'm chasing at the moment.

[HomeMadeSin]

Seriously considering the big thirsty 8.1 Vortec.....

[jocko]

SM420,465,3 OTT, TH350, and TH400 all have the exact same effect on fuel economy on the highway. You hit the nail on the head: 4.56.... even an overdrive trans will suck for fuel economy with a 4.56. I recommend a rear gear or whole rear end swap if you’re trying to reduce highway rpm a noticeable amount. How much of a higher gear depends on how you plan to use the truck and whether or not you plan to add an overdrive trans in the future. Personally, I’d just swap the rear gears to a manageable highway ratio and let the granny gear worry about the occasional stump pulling if required.

['68OrangeSunshine]

I used to run a '67 K/10 Suburban,
I called it ''White Fang'' after that big dog in the Jack London book. It had a huge appetite for 91 octane fuel, due to the PO shoehorning a junkyard '77 BBC 454 under the hood. He had it lashed into a TH350/NP205 and 3.73 geared-differentials [fore and aft] on 33x12.50x15LT tires. Sucker would pass anything on the road but a gas station.
As 68TT has noted, things get modified over the course of time
The guy I bought it from said he took out the 283 and SM420, and first went with a 350/TH350/NP205, but his reason for having that big a truck was to run the family and boat up the mountains to Pinetop from Mesa AZ. Although they are only 150 -180 miles apart, that trip runs thru an elevation change of 5,550', When he found the 350 wouldn't run his boat up the hill as fast as he wanted, he found a 454. [Don't know if the boats got progressively bigger, too, but it would figure.]
I did rebuild the 12-Bolt 3.73 rear end, adding in new Moser 6-lug axles and an Auburn posi.
The doghouse (front body clip) would shimmy and bop like a go-go dancer once over 80 MPH. He never bothered to build up the front leaf springs to cope with the heavier big block. Stopping was another issue. Drum brakes all around, but being a K/truck the front drums were an oddball size.
Rear drums were the same as my '68 C/10 Stepside -- which did just fine with drum brakes if well kept up.
Sometimes in that Sub, I'd have to select the softest target to plow into.
Never came to that, but it would be a lot better if I felt more secure with a post-'69 Dana 44 front with power disc brakes and powersteering. The automatic would not work for engine braking, it would just shift up by itself.
I stopped running that rig after I had an engine fire on an away job, one state over. I towed it home, but foolishly made a claim on my insurance and they totalled it, and sold it back to me as a salvage title. Since gas was rapidly rising, I saw no sense in rebuilding an engine that got 6 MPG City, and 8 highway.
So White Fang has lain fallow, while I run a Stepside and a '71 Jimmy K/1500.
Someday, when my ship comes in...

[HomeMadeSin]

The front drums are definitely getting discarded. Will make a visit to a salvage yard or two this weekend and see what turns up. Got her on 4 dollies in the garage now - that was fun to do solo. But out of sight from the neighbors and can focus on getting things moving.

Definitely want to get her moving first and do upgrades over time. The 8.1 liter looked good because they are cheaper than the mainstream sizes, but that ratio would drink fuel. Hmmm.....

[LONGHORN1962]

An sm420 will have reverse to the left and down, sm465 is to the right and down.

[HomeMadeSin]

['68OrangeSunshine]

420

[HomeMadeSin]

Yes sir. And here's the driver side head casting number:



Blah.

[GASoline71]

One of the most common 350 head castings GM ever produced. Nothing special 1.94's and probably 76cc chambers. They fit right in with the fact that it's a 1977 350 block.

Gary