I was at my local car show the other day and I talked with a guy who built an inline Chevy 6 for his street rod. I was interested in the engine because it’s different. I’m getting tired of seeing small-block Chevys and LS engines everywhere. I don’t know much about these engines. Are they worth building for a mild rat rod?
Jeff Smith: There is a whole subculture of hot rods out there running around with “alternative” engines. While most street rods built before WWII were Flathead-powered inline fours and later V8 Fords, Chevrolet was always considered a very conservative company with inline six-cylinder engines with overhead valves. The biggest drawback to an inline six is its physical length and it will be smaller in displacement because it only has six cylinders. But for a lightweight street rod with an open engine bay, a Chevy six could be a great engine. We’ll go over some material for the Chevy 6 as it’s the most popular—but the AMC, Ford, Pontiac OHC 6, Mopar slant six, and Jeep engines are other obvious candidates.
If you’re into a dramatic-looking engine, consider the Pontiac Overhead Cam (OHC) inline six that came in the 1966-67 Tempest and 1967 Firebirds. These engines are very modern looking with the factory ribbed cam and front timing belt covers. There was power with this engine as well—in 1967 the 230-cubic-inch Pontiac OHC 6 was rated at 215 horsepower with 240 ft.-lbs. of torque, a Rochester Q-jet four-barrel carb, and 10.5:1 compression. There are parts available for these engines, although usable core engines are becoming scarce.
As we mentioned earlier, Chevy has built overhead valve inline sixes since 1929, but we will deal with only the later model engines used from 1962. This lineage of Chevy inline six came in four different bore/stroke/displacement combinations: 194, 230, 250, and 292 cubic inches. The largest was used only in Chevy pickups because of its taller deck height. The deck height allowed a very long 4.12-inch stroke compared to 3.25 for the 230, which is probably the most common of the Chevy sixes that you’ll find. The 230-cubic-inch engine came in mid-1960s passenger cars like the Chevy II, Camaro, Chevelle, and some full-size cars as well. It was rated at 140 horsepower with a one-barrel and 155 horsepower with a two-barrel carburetor and 8.5:1 compression.
All early Chevy six engines place the intake and exhaust manifolds on the driver side of the engine. This is not the optimal placement for the intake since the exhaust puts lots of heat directly into the intake manifold, which hurts power. But the good news is there are lots of parts available for these engines. Offenhauser offers a single four-barrel intake manifold, several companies grind cams, and there are headers available. Keep in mind that most headers will be designed for pickups and it’s probable that they may need tweaking to fit other chassis.
One odd thing about the Chevy six is its paired intake ports. Three common ports feed all six cylinders. Worse yet, a head bolt boss intrudes into these ports, restricting flow. We discovered a small company in Iowa called AutoWerks (12bolt.com), owned by Tom Lowe. Lowe has spent several decades working on these little six cylinders. He has developed a part called The Lump. Its name is descriptive, if not necessarily attractive. Lowe’s approach was to remove the large cast iron boss that surrounds the stock head bolt. He then spot faces the bottom of the port for an Allen head bolt and places an aluminum cover (The Lump) over the Allen bolt head to improve airflow. The conversion can be done on your workbench and the increase in airflow is significant enough to reward the effort. You can check out an installation video and all the particulars on Lowe’s website 12bolt.com. Lowe also offers a new intake called the P.E.S. Ram that is about the best looking Chevy inline intake I’ve seen.
For power, a mild street V8 will make roughly 1.1 hp per cubic inch with stock heads. The heads on these older Chevy six cylinders are not very good so making 1.1 is about the most you can expect. With a 230-cubic-inch inline six with a mild cam, headers, and the cylinder head work we’ve described, you could expect to make around 250 to perhaps 260 horsepower. Because the inline six crankshaft is so long, even with 7 main bearings it’s probably not a good idea to spin these engines much beyond 6,000 rpm.
Overall, internal parts are readily available and they’re not overly expensive so you could assemble a decent performance street inline Chevy six without draining your bank account. It might be a fun adventure and surely one to garner more attention than just another small-block.