Getting MPG down

[Supercuda]

In the 80's, there was a factory 318-4V engine, and I have seen it quoted variously as having 360 heads, and as just having the 360-4 intake. I haven't investigated any further, as most have been in running trucks, but there are some cop cars out there like this, and I am sure that somebody has torn down one of these engines and found out the truth. The port mis-match isn't a huge consideration, and will generally only affect idle quality. As the intake flow increases, the ledge in the flowpath will matter less. An ideal situation for optimum intake efficiency and power with a little economy, is to have the opposite effect, with the intake runners smaller than the ports in the heads. This creates a reversion dam, which partially cancels out the pressure wave generated by the closing intake valve. It has the overall effect of a subtle "ram-tuning" of the intake, not timing the pulses in each runner to "stack up", supercharging the intake flow, but by dampening a detrimental result of the dynamics of a running engine.

[71chally416]

  On the flow bench you find most of the airflow of a rectangular port is in the middle of the port and less so in the corners.

I think what you'll find on the later 318's that had the 4 bbl in the trucks and vans is they also have the 360 smogger heads. It was probably more Chrysler phasing out the old 318 heads and using up the parts they had than anything else, or just that they wanted to stock one part instead of two(?) The later "Magnum" 318-360's both used the same larger port heads.