Start With The Architecture
The Gen III/IV LS family keeps a 4.400-inch bore-center layout and roughly 9.240-inch deck height across the platform, but displacement, block material, crank/cam signals, intake-port shape and factory controls vary enough that an RPO code is more useful than simply saying “5.3” or “6.0.”
Common Gen III / Gen IV LS & Vortec Variants
| RPO | Displacement | Gen | Block | Bore × Stroke (in) | Intake Port | Reluctor | AFM/DOD | VVT | What it means |
|---|---|---|---|---|---|---|---|---|---|
| LR4 | 4.8L / 293 | III | Iron | 3.780 × 3.267 | Cathedral | 24x | No | No | Early truck 4.8; short-stroke member of the 3.78-inch-bore family. |
| LM7 | 5.3L / 325 | III | Iron | 3.780 × 3.622 | Cathedral | 24x | No | No | Very common truck 5.3; broad donor availability. |
| L59 | 5.3L / 325 | III | Iron | 3.780 × 3.622 | Cathedral | 24x | No | No | Flex-fuel sibling of LM7 in many applications. |
| LM4 | 5.3L / 325 | III | Aluminum | 3.780 × 3.622 | Cathedral | 24x | No | No | Lightweight aluminum 5.3; less common than LM7. |
| L33 | 5.3L / 325 | III | Aluminum | 3.780 × 3.622 | Cathedral | 24x | No | No | High-output aluminum 5.3 truck engine. |
| LQ4 | 6.0L / 364 | III | Iron | 4.000 × 3.622 | Cathedral | 24x | No | No | Workhorse 6.0; lower compression than LQ9 in typical factory form. |
| LQ9 | 6.0L / 364 | III | Iron | 4.000 × 3.622 | Cathedral | 24x | No | No | Higher-compression Gen III 6.0 used in performance-oriented trucks/SUVs. |
| LY2 | 4.8L / 293 | IV | Iron | 3.780 × 3.267 | Cathedral | 58x | No | No | Early Gen IV 4.8. |
| L20 | 4.8L / 293 | IV | Iron | 3.780 × 3.267 | Cathedral | 58x | No | Yes | Later Gen IV 4.8 with VVT in truck applications. |
| LY5 | 5.3L / 325 | IV | Iron | 3.780 × 3.622 | Cathedral | 58x | Yes | No | Gen IV iron 5.3 commonly paired with AFM. |
| LMG | 5.3L / 325 | IV | Iron | 3.780 × 3.622 | Cathedral | 58x | Yes | No | Flex-fuel Gen IV iron 5.3; commonly AFM-equipped. |
| LH6 | 5.3L / 325 | IV | Aluminum | 3.780 × 3.622 | Cathedral | 58x | Yes | No | Aluminum Gen IV 5.3 used in SUVs/trucks. |
| LC9 | 5.3L / 325 | IV | Aluminum | 3.780 × 3.622 | Cathedral | 58x | Yes | Yes* | Aluminum/flex-fuel 5.3; feature set varies by model year/application. |
| LY6 | 6.0L / 364 | IV | Iron | 4.000 × 3.622 | Rectangle | 58x | No | Yes | HD truck 6.0; rectangle-port heads and VVT. |
| L96 | 6.0L / 364 | IV | Iron | 4.000 × 3.622 | Rectangle | 58x | No | Yes | Later HD 6.0; Chevrolet Performance lists 9.7:1 compression for its L96 crate package. |
| L76 | 6.0L / 364 | IV | Aluminum | 4.000 × 3.622 | Rectangle | 58x | Yes | Yes* | Used in car and truck applications; hardware/controls vary by application. |
| L92 | 6.2L / 376 | IV | Aluminum | 4.065 × 3.622 | Rectangle | 58x | No | Yes | Early Gen IV truck/SUV 6.2; large rectangle-port heads. |
| L9H | 6.2L / 376 | IV | Aluminum | 4.065 × 3.622 | Rectangle | 58x | No | Yes | 6.2 truck/SUV variant; no AFM in common applications. |
| L94 | 6.2L / 376 | IV | Aluminum | 4.065 × 3.622 | Rectangle | 58x | Yes | Yes | 6.2 truck/SUV variant with AFM and VVT. |
| LS1 | 5.7L / 346 | III | Aluminum | 3.898 × 3.622 | Cathedral | 24x | No | No | Original production LS-family performance engine. |
| LS6 | 5.7L / 346 | III | Aluminum | 3.898 × 3.622 | Cathedral | 24x | No | No | Higher-output Gen III car engine; 243/799-style head family is popular in swaps. |
| LS2 | 6.0L / 364 | IV | Aluminum | 4.000 × 3.622 | Cathedral | 24x/58x* | No | No | Transition-era engine; reluctor/sensor details must be verified by exact year/application. |
| LS3 | 6.2L / 376 | IV | Aluminum | 4.065 × 3.622 | Rectangle | 58x | No | No | Chevrolet Performance lists 10.7:1, 430 hp crate configuration, 58x reluctor. |
| L99 | 6.2L / 376 | IV | Aluminum | 4.065 × 3.622 | Rectangle | 58x | Yes | Yes | Automatic-Camaro sibling to LS3 with AFM/VVT. |
| LSA | 6.2L / 376 | IV | Aluminum | 4.065 × 3.622 | Rectangle | 58x | No | No | Factory-supercharged; Chevrolet lists 9.1:1 compression. |
| LS9 | 6.2L / 376 | IV | Aluminum | 4.065 × 3.622 | Rectangle | 58x | No | No | Factory-supercharged Corvette engine; forged rotating parts in Chevrolet Performance spec. |
| LS7 | 7.0L / 427 | IV | Aluminum | 4.125 × 4.000 | Raised/unique | 58x | No | No | Large-bore 7.0; unique raised-port/bolt-pattern considerations. |
*Transition-year and application exceptions exist. LS2 is the classic example: do not buy a harness/controller based only on the “Gen IV” label. Physically verify crank/cam sensing and reluctor arrangement.
What Bore And Stroke Actually Change
Bore
A larger bore increases displacement and can provide more room around the valves. The 6.0's 4.000-inch bore and 6.2's 4.065-inch bore are a major reason those engines pair naturally with larger rectangle-port cylinder heads.
Stroke
Stroke is how far the piston travels. The 4.8 uses a shorter ~3.267-inch stroke, while most 5.3/5.7/6.0/6.2 engines use a ~3.622-inch stroke. That is why a 4.8 and 5.3 can share a 3.78-inch bore yet have different displacement.
4.8: 3.78 bore × 3.267 stroke ≈ 293 ci. 5.3: the same 3.78 bore with a 3.622 stroke ≈ 325 ci. 6.0: 4.00 × 3.622 ≈ 364 ci. 6.2: 4.065 × 3.622 ≈ 376 ci. LS7: 4.125 × 4.000 ≈ 427 ci.
Port Families Matter Before You Buy An Intake
ICT Billet’s LS intake-port guide groups most Gen III engines as cathedral-port and many Gen IV engines as rectangle-port. LS7/selected LSX heads use a raised-port arrangement and different bolt location, so an LS7 intake is not a direct bolt-on to standard LS3 heads.
- Cathedral examples: LS1, LS2, LS6, LR4, LM7, LQ4, LQ9, LY5, LMG, LC9.
- Rectangle examples: LS3, L99, LSA, L92, L94, L96, LY6, LS9.
- Raised/unique: LS7 and selected LSX combinations.
RPO Code Beats The Valve-Cover Sticker
When buying a used engine, record the block casting, crank sensor color/location, cam sensor location, intake-port shape, throttle-body type and whether AFM/VVT hardware is present. That prevents the most expensive kind of swap mistake: buying the wrong controller, harness, cam timing set or intake because a seller called everything a “5.3 LS.”