GM 8.1L Vortec L18 V-8

8.1L Vortec V-8 Specifications and Information

496 cubic inches; what more needs to be said about GM's big block of big blocks? The 8.1L Vortec V8 is far from lacking in the horsepower and torque departments, although fuel mileage might not be much to write home about. On that note, this might be one of those engines you'll only want to start when you really need to. Although it might not be the best for running errands around town, the 8.1L V-8 is (was) a potent alternative to the more expensive 6.6L Duramax diesel option. It was originally introduced as a heavy duty replacement for the long running 454 CID big block (7.4L). The engine peaked at 340 horsepower and 455 lb-ft during its 6 year stint as the biggest engine option for 2500HD and 3500HD models from Chevrolet and GMC.

For a gas engine, the 8.1L displays an impressively flat torque curve, coming on strong in the 1,200 to 1,400 RPM range and finally tapering off below 400 lb-ft just after 4,000 RPM. That's a span of 2,600 RPM of usable torque greater than 400 lb-ft, peaking at 440 - 455 lb-ft (depending on model year) at a respectable 3,200 RPM. Horsepower continues to climb until 4,200 RPM, peaking in the 320 to 340 range.

In addition to 2001 to 2006 model year Chevrolet and GMC trucks/SUVs/vans, the engine is found in the medium duty Kodiak, marine, and various motorhome chassis's. In fact, the engine was manufactured until 2009 for motorhome and various marine applications. The 8.1L is a big bore, big stroke engine with a near square bore-to-stroke ratio and a ~5,000 RPM redline. The engine was only ever been offered mated to General Motor's 4L85E four speed automatic transmission - a manual transmission rendition was never offered.

When broken down, GM's 8.1L is largely a stroked out version (4.00" vs 4.37") of the company's 7.4L Vortec V-8, which was retired in favor of the 496 cubic inch behemoth. Both engines share a 4.25 inch bore, and the undersquare design of the 8.1L improves low end torque and helps flatten the torque curve, both of which are ideal characteristics for a heavy truck engine.

In the wake of fuel economy and emissions standards, General Motors would ultimately retire the engine from their 2500/3500HD lineup in favor of a smaller 6.0L powerplant. While the engine produces a considerably lower 360 peak horsepower and 380 lb-ft peak torque, General Motors possesses the powerful 6.6L Duramax diesel for applications that require serious towing capability.

GM 8.1L Vortec V-8 Engine Specs (Vortec 8100)


General Motors Vortec 8100


90° V-8

Years Produced:

2001 - 2006 Chevrolet/GMC 2500/3500 trucks, vans, and SUVs
• Silverado and Sierra 2500HD/3500HD
• Suburban and Yukon 2500
• Avalanche 2500
• Express 2500/3500
• Medium Duty Chevrolet Kodiak

Various marine and motorhome applications from 2001 - 2009

RPO Code:



496 CID (495.95)
8.1 liters (8.1266)

Cylinder Head Material:

Cast iron

Engine Block Material:

Cast iron

Compression Ratio:

9.1 : 1

Firing Order:

1 - 8 - 7 - 2 - 6 - 5 - 4 - 3

Cylinder Bore Dia:

4.250 in (107.95 mm)

Cylinder Stroke Len:

4.370 in (110.99 mm)


Naturally aspirated

Fuel System:

Sequential multi-port fuel injection


2 valves per cylinder, OHV, typical cam-in-block pushrod engine

Oil Capacity:

6.5 US quarts w/ oil filter

Fuel Requirements:

Regular 87 octane unleaded gasoline

Max Engine Speed:

5,000 RPM (truck, van, SUV applications; governed speed may vary in marine, motorhome, and medium duty applications)

Peak Horsepower:

330 - 340 hp @ 4,200 rpm (truck, van, SUV applications)

Peak Torque:

440 - 455 lb-ft @ 3,200 rpm (truck, van, SUV applications)

8.1L Vortec Horsepower and Torque Curves

GM 8.1L V-8 horsepower and torque curve chart

2006 8.1L Vortec V-8 Horsepower and Torque Curve Chart

8.1L Vortec vs 6.6L Duramax

Sheer displacement contributes largely to the 8.1L's relatively high peak torque rating, which came within 50 lb-ft of the Duramax diesel in the early model years. Moreover, the engine makes peak torque at a reasonable, practical 3,200 rpm. These characteristics are favorable in truck applications. While the 8.1L outpaced the Duramax through 2005 in the horsepower department, the Duramax maintained several important advantages - fuel economy and low end torque. Significantly less displacement (6.6 vs 8.1 liters) and the higher thermal efficiency the diesel offers contribute largely to unmatched fuel economy. The 8.1L V-8 is known for many things, however fuel economy is not one of them and the engine has a tendency to guzzle fuel at a high rate.

Model Year

8.1L Vortec Horsepower & Torque

6.6L Duramax Horsepower & Torque


340 hp @ 4,200 rpm

455 lb-ft @ 3,200 rpm

235 hp @ 2,700 rpm

500 lb-ft @ 1,600 rpm


340 hp @ 4,200 rpm

455 lb-ft @ 3,200 rpm

235 hp @ 2,700 rpm

500 lb-ft @ 1,600 rpm


340 hp @ 4,200 rpm

455 lb-ft @ 3,200 rpm

235 hp @ 2,700 rpm

500 lb-ft @ 1,600 rpm


320 hp @ 4,200 rpm

440 lb-ft @ 3,200 rpm

310 hp @ 3,000 rpm

520 lb-ft @ 1,600 rpm


320 hp @ 4,200 rpm

440 lb-ft @ 3,200 rpm

310 hp @ 3,000 rpm

520 lb-ft @ 1,600 rpm


320 hp @ 4,200 rpm

440 lb-ft @ 3,200 rpm

360 hp @ 3,200 rpm

650 lb-ft @ 1,600 rpm