243 vs 799 vs 706 vs 317 heads
All four are cathedral-port LS heads:
| Casting | Chamber | Found on | Notes |
|---|---|---|---|
| 243 | 64 cc | LS6, LS2 | Best-flowing common cathedral head |
| 799 | 65 cc | Aluminum 5.3 trucks (e.g., L33) | "Truck 243": nearly identical ports; lacks LS6 valve springs/lightweight valves |
| 706 | 61 cc | 4.8/5.3 trucks | Small chambers, 1.89/1.55 in valves; good for raising compression |
| 317 | 71 cc | Iron 6.0 trucks (LQ4) | Large chambers, lower compression (boost-friendly) |
Speedway's 5.3 project with lightly shaved 706 heads and a BTR Truck Norris cam made about 430 hp. For a 5.3 upgrade, 243/799 heads are the classic budget swap. Rectangle-port heads (823 etc.) need a rectangle-port intake.
Confidence: medium — sources disagree or are limited; check the sources below.
Related questions
- Which LS engine is best for turbo/boost?
- How much horsepower does a stock 5.3 make?
- How much horsepower can a stock 5.3 handle?
- How much boost can a stock 5.3 handle?
- Junkyard 5.3 turbo build: what do you need?
- Best cam for a 5.3
Sources
- General Motors LS-based small-block engine — Engine table — Wikipedia
- Best LS Heads for 6.0/5.3/4.8 | Cathedral Port Heads vs Rectangular — Speedway Motors
- Decoding LS Head Casting Numbers — Malex Motorsports