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GMC L29 specs: 454 ci (7.4L) 8-cylinder, 4.251 x 4.00 in (108 x 101.6 mm) bore and stroke, 9:1 compression. Rated 290 hp, 1999–2000.
The GMC 454ci (L29) is oversquare — the 4.251" bore exceeds the 4" stroke by 6.3% — a layout that favors airflow and RPM over leverage at the crank. The 4" stroke puts mean piston speed at 4,000 ft/min around 6,000 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.534 is short — higher piston acceleration and more side-load, typical of stroker combinations and a reason to watch piston speed closely. Each of the 8 cylinders displaces 56.8 ci (930 cc).
9:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 3 engines in the GMC 454ci family, all of them 454 ci — the differences between them are in compression, heads and rating, not displacement. 2 factory variants share these dimensions, rated at 290 hp across 1999–2000.
| Displacement | 454 ci / 7.4 L |
|---|---|
| Bore | 4.251" |
| Stroke | 4" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 9:1 |
| Rod length | 6.136" |
| Rod ratio | 1.534 |
| Bore/stroke ratio | 1.063 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Firing order | 1-8-4-3-6-5-7-2 |
| Advertised HP | 290 hp |
| Years | 1999–2000 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 1999 | L29 net | 290 @ 4000 | 410 lb-ft @ 3200 | — |
Factory specification sheet.
| Bore/stroke character | 1.063 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 4,000 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.534 — short — more side loading and piston dwell at TDC, typical of stroker combinations |
| Displacement per cylinder | 56.8 ci |
| Static compression | 9:1 — low by modern standards, generally happy on regular pump fuel |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1999 | 290 hp | L29 |
| 2000 | 290 hp | L29 |
2 factory vehicles, 1997–2000. Each year opens that model's engine table.