94 K2500 350 "heavy duty"?

[Kennyray]

The difference between 6 lugs and 8 apply to the 2500

[jbarker]

The plot thickens. Chilton GM full size trucks 88-98 (book #28624) p 1-9 general engine specs for the 5.7 TBI calls out a comp ratio of 9.1:1 with a footnote #8. The footnote #8 reads, "heavy duty 8.3:1". So in my mind heavy duty is not just the frame/suspension, it's the engine also. So I go to p 3-6 for the engine specs: 5.7L VIN K comp ratio 9.4:1 (huh?), no footnotes for HD. Bore 4.00" stroke 3.480". So comp ratio difference must be a difference in the head. I was buying engine parts and kept running into the HD/non-HD question on AutoZone's computers & I was not buying heads. The engines must differ. So where is the RPO code for that?
What am I missing here? BTW VIN R 5.7 same 9.4:1 comp and bore/stroke.
JB

[1500cheyenne96]

The only code i can find for HD 5.7L is LT9 but that lists as "V8 5.7L 4BBL HD" so i doubt that has any thing to do with your truck but the list could be wrong also look for MT1 that lists as "transmission heavy duty THM 4L80E" I don't know if the means just the normal 4l80E or if that it the HD variant of it and from what i can find the 6 lug 2500's were the equivalent of the todays 1500HD

[jbarker]

No code LT9 but I do have code MT1. Based on the link posted earlier in this thread,this is a tranny code and seems to have a half dozen different meanings.
I'll crawl under the truck this weekend and count bolt heads.

Any idea what the comp ratio is supposed to be on an LT9?

Maybe someone replaced the glovebox on my truck . . .
JB

[1500cheyenne96]

The book i have says its 8.2:1 and i'm an idiot it's the engine for HD trucks from 79-87

[jbarker]

GM-Trucks.com| RPO Code Lookup

So I worked a little on the hyperlink above on a few of the codes in my glovebox sticker. For example, G80 (which is on my list in the glovebox) could be (copied verbatim from website):
G80 Differential, heavy-duty locking rear
G80 Differential, automatic locking rear
G80 Differential, heavy-duty automatic locking rear
G80 Differential, limited slip rear
G80 Differential, limited slip
G80 Differential, locking, heavy-duty, rear
G80 Differential, Zexel-torsen, limited-slip, rear
G80 Differential, automatic
G80 Rear Axle: Positraction
G80 Locking, Rear Axle
G80 Axle Positraction Limited Slip
G80 Differential, locking, rear
G80 AXLE POSITRACTION LIMITED SLIP

As I inferred before, I am a ******* newbie to RPO codes (but I am getting a lot smarter really fast with every post from this forum). The list above does not help much in the HD/non-HD differentiation.

Unless, do all of the above descriptions mean the same hardware?
Seems impossible - limited slip is in no way the same as locking, for example. Therefore, what information do the RPO codes really impart? Family?

[1500cheyenne96]

Thats all the different variants as Gm used the G80 axle in in the vette, Z28, SS, Trans am, impala, caprice light and medium duty trucks your truck probably has the limited slip version of the G80

[crabtruck]

With regards to "HD" in 94 CHVs:
This only applied to the 5.7 (350) eng.
The purpose was to adjust for over/under 8,500 GVW.

3 flavors: 5.7 w/MT-not hd, 5.7 w/MT-HD, 5.7 w/AT-HD or not.
No "HD" with other engines gas. (for eng diffs)
Unless you like a "typo" I found in factory book saying there's 4.3HD.
Diesels had the courtesy to use 3 VINs: P=L49,F=L65turbo,S=L56turbo - S is the HD.
(And nobody sees the Y=L57 nat. asp'd. )

HD is primarily a weight cutoff for smog purposes in 1994.
HD will use a different EGR, has no Evap Purge Cntrl, etc.
If that's what you're working on, then it's a good time to bring
your EGR to compare, that are about 5 different types used.
HD have 8.3:1 vs 9.1:1 said above via head, not cyl.
LD valve guides are simply bored holes,
HD exhaust valves use seperate pressed in valve guides
and are serviceble.
Exhaust only not both like 7.4.

HD for tran, frame and suspension is seperate game.
Also paint has extra layer of wax becaise they know
it's not going to happen again.

JB: the MT1 code is for an auto trans HD 4spd w/OD
(as opposed to the M30 which is same but LD)
An MG5 is the MT HD 5spd w/OD.
Q4B is 6,200 LBS GVW (LD)
You may see the NA4 HD code as well.

[BernieB]

Originally Posted by crabtruck

With regards to "HD" in 94 CHVs:
This only applied to the 5.7 (350) eng.
The purpose was to adjust for over/under 8,500 GVW.

3 flavors: 5.7 w/MT-not hd, 5.7 w/MT-HD, 5.7 w/AT-HD or not.
No "HD" with other engines gas. (for eng diffs)
Unless you like a "typo" I found in factory book saying there's 4.3HD.
Diesels had the courtesy to use 3 VINs: P=L49,F=L65turbo,S=L56turbo - S is the HD.
(And nobody sees the Y=L57 nat. asp'd. )

HD is primarily a weight cutoff for smog purposes in 1994.
HD will use a different EGR, has no Evap Purge Cntrl, etc.
If that's what you're working on, then it's a good time to bring
your EGR to compare, that are about 5 different types used.
HD have 8.3:1 vs 9.1:1 said above via head, not cyl.
LD valve guides are simply bored holes,
HD exhaust valves use seperate pressed in valve guides
and are serviceble.
Exhaust only not both like 7.4.

HD for tran, frame and suspension is seperate game.
Also paint has extra layer of wax becaise they know
it's not going to happen again.

JB: the MT1 code is for an auto trans HD 4spd w/OD
(as opposed to the M30 which is same but LD)
An MG5 is the MT HD 5spd w/OD.
Q4B is 6,200 LBS GVW (LD)
You may see the NA4 HD code as well.

Ya know... I had to take calculus twice in college before I passed the course, but this actually makes perfect sense.

[crabtruck]

I do apologize for that.