Hotrod Magazine Slant Six Build Up

Good question. I also was surprised that the Dutra-Duals gave minimal improvement, but they may only work as a system, so a fairer comparison might have been w/ the 4 bbl carb & shortie intake w/ and w/o the Dutras. The head gasket failed before they evaluated the long-runner Hurricane 4 bbl intake, and you can't buy the gasket for the alum engine at Autozone, so they stopped. My understanding is that long runners help most in mid-range (organ-pipe effect), so unlikely they would have done much at high rpm where max power occurs, though might have upp'ed max torque. Newish cars with variable intake manifolds have valves which switch from long runners to short as rpm increases. But, w/ a carburetor, the long runners give more time for the gas drops to vaporize and the Hurricane might also give more-even fuel distribution between cylinders.