Chevy 250 I-6 History
The Chevy 250 is part of the General Motors third-gen inline-six platform, which was introduced in 1962. The 250 itself became available in the lineup in 1966 due to the demand for a larger motor on the familiar platform. Contrary to popular belief, the 250 was not the largest of the third-gen Chevy sixes; that title goes to the Chevy 292 engine.
Other engines in the series include the 3.2-liter 194 and the 3.8-liter 230 (not to be confused with the later GM 3.8-liter V6). Chevrolet discontinued the 250 in 1979 for passenger cars and 1984-5 for trucks. Base-model vehicles once equipped with the 250 switched over to the 4.3-liter V6. Interestingly, GM continued manufacturing the third generation inline-six in Brazil until 2001.
Chevy 4.1L Specifications
The Chevy 250 straight-6 engine was a single-cam overhead-valve inline-six. It originally produced 155 horsepower and 235 lb-ft of torque with a one-barrel Rochester Monojet carburetor. The 250 was a stroked version of the smaller 3rd generation GM six-cylinder engines. The 250 has a bore of 3.875 inches (98.425mm) and a stroke of 3.53 inches (89.662mm).
ENGINECHEVY 250 INLINE-SIXMANUFACTURERGENERAL MOTORSYEARS PRODUCED1966 to 1984DISPLACEMENT250CI (4.1L)CONFIGURATIONINLINE SIXFUEL TYPEGASOLINECOMPRESSION RATIO8.5:1FIRING ORDER1-5-3-6-2-4BORE3.875 INCHES (98.425 MM)STROKE3.53 INCHES (89.662 MM)HORSEPOWER (1970)155 HP (115.58 kW)TORQUE235 LB-FTGAS MILEAGE13-22 MPG (EST)
The firing order of the 4.1L straight-six is 1-5-3-6-2-4. Owners could achieve fuel economy of around 13 city and 20 highway. Some of the fuel economy issues of the 250 were due to high rear-end ratios, especially in pickup trucks. The design of the 250 was loosely based on older GM engines that date back decades.
Chevy 250 Applications in Cars
General Motors also used the 250 in passenger coupes and sedans. The 250 I6 was a base-model option in mid and full-size cars from 1966 to 1979. GM phased out the 250 in favor of small V6, V8, and I4 engines such as the Chevy 305 and the GM Iron Duke inline-four.
In passenger cars, the 250 straight-six was most often mated to a three-speed manual transmission or a three-speed Turbo-Hydramatic automatic.
Chevy 250 Applications in Trucks
The Chevy 4.1-liter/250 was used in numerous vehicles, especially Chevy and GMC pickup trucks. Base model trucks used the engine from 1966 to 1984. It was available in most base-model GM half-ton trucks and often coupled to a three-speed manual column-shifter transmission.
Some Chevy 250 engines came mated to the venerable TH350 three-speed automatic transmission, and others came with the SM465 four-speed ‘granny’ manual transmission. The 250 was available in both two-wheel-drive and four-wheel-drive pickup trucks during the 1960s, 1970s, and 1980s.
Chevy 250 Reliability
Is the Chevy 250 a good motor? History says that it is. The Chevy 250 proved to be a reliable engine and stayed in U.S. production for nearly two decades. Owners affectionately referred to the 250 as a ‘sewing machine’ due to its simplicity and reliability.
One of the primary reasons why the 250 worked so well was its simplicity, as these engines were easy to maintain. All parts are accessible in the large engine bays of the time, as the engine was far narrower than typical V8s. And while some would argue that the Chevy 250 six wasn’t as physically durable as the competing Ford 300, it was still a robust engine that held up well to abuse.
Common Chevy 250 Problems
As stated previously, the Chevy 4.1L inline-six was mostly reliable across the board. The engine itself had few long-running problems, helping it earn a reputation for reliability. The engine suffers from the same problems that any other carbureted engine from the time had, which were often related to the fuel and ignition systems. Vehicles equipped with the 250 broke down no more (or less) than any other typical GM car from the time.
250 Inline-Six Performance Builds and Upgrades
Performance parts are available for the 250 six-cylinder engine. The easiest way to improve the power output and reliability of the 250 is to upgrade the fuel and ignition systems. Here are three examples of performance and reliability builds for the Chevy 250. This is not an exhaustive list, but it may give you a few ideas before you start your project.
Basic ‘Daily Driver’ Chevy 250 Reliability Build
This is the Chevy 250 basic reliability build, which is a cheap and quick way to modernize your 250. Anyone with basic tools can do this build. If the engine was built before the mid-1970s, it probably has ignition points. Points systems are fine, but electronic ignition is less temperamental and more reliable.
Additionally, rebuilding or replacing the original Rochester Monojet 1-barrel carburetor is often a good idea. Here’s what you need for the basic reliability build.
- Fuel Filter
- Open-Element Air Cleaner
- Pertronix Ignitor Electronic Ignition Kit (Optional)
- Distributor Cap and Rotor
- Ignition Coil
- Remanufactured Rochester Monojet 1-Barrel Carb (or Rebuild Kit)
- Intake/Exhaust Gasket Set
- Replacement Hoses
- Plugs and Wires
The reliability build is little more than a glorified tune-up, but it can significantly affect driveability. This build can (or parts of it) be accomplished for a few hundred dollars. It’s ideal for when you first purchase a vehicle equipped with a 250 I6, and should provide long-lasting reliability.
Mild 250 Straight-Six Performance Build
The Chevy 250 mild performance build attempts to make this normally gutless engine more ‘streetable’ in modern traffic. This build is ideal for pickup trucks whose owners are used to driving V8s, though it will produce nowhere near the power that a built 350 will. Still, the power gains from these modifications will be noticeable and a vast improvement from stock.
- Offenhauser four-barrel intake manifold
- Holley 350 Four-Barrel Carburetor
- Summit Racing Brand Headers
- Two 18” Glasspack Mufflers
This is a great basic engine build at a relatively low cost. Installation is easy, especially on pickup trucks. Modifications of this type (especially with long glasspack mufflers) make the engine sound like a tractor under load, and the exhaust note has that distinct ‘classic car’ feel.
Hot Rod Chevy 250 Build
If you want to build a hot rod Chevy 250 motor, you can—companies still manufacture some pretty radical camshafts for these motors. You’ll want to port and polish the cylinder head as well, which any machine shop should be able to do. Some people even ‘poke and stroke’ these motors, which is a great way to add power. Remember, there’s no replacement for displacement.
Chevy 250 Resources
The 250 inline-six has a pretty large following on the forums. A great place to find tips and know-how is the 67-72 Chevy Trucks Forum, along with the Squarebody Forum and Jalopy Journal. Performance builders would benefit from purchasing the Chevrolet Inline Six-Cylinder Power Manual by Leo Santucci Amazon. Other resources include vintage shop manuals, which can be found on eBay for around $10.