"Blither blither".... whoa hold on a second.
Where did you get the idea that you would want or need a 1 1/2 primary tube header ?
*The 318 ports are the same
*you'll actually only lower peak torque and hit it sooner in the rpm range.
Well, it all started with an article in Hot Rod, which was "10 Steps to Power", and they suggested that on a daily-driven street car, moving down a step in primary header tube size would yield more real-world power on the torque side of things, since focus would not be on top-end on city streets. They suggested on a typical SBC, to move down to 1-1/2" primaries to get that torque at a lower portion of the RPM range, as you mentioned. I agree with this, especially on a 2-barrel powered 273.
I'm not engineer, but wouldn't increasing the primary tube size to something which is larger than the exhaust port equivalent be a detriment to the motor unless, you are going for high rpm?
