They all came with a four barrel. Only the 283 came with a two barrel. Base horsepower was the 275 horse engine. There was also a 300 horse a 350 horse and a 375 horse variant. The two top engines had camel hump heads and mechanical valve tappets instead of hydraulic, the 375 was a Corvette only option and was fuel injected, and the 350 horse was equiped with a Holley. The two lower horse variants had a small triangle on top of the base rectangle called a Power Pack head and used a Rochester Quadrajet.