Engines are interesting. Not only are they great mechanical beasts that make power, but they are arguably one of the more misunderstood items in our lives. Regular people have little or no clue on how an internal combustion engine actually works, and the sad thing is that many enthusiasts have only enough knowledge to make them dangerous. Engines are riddled with old wives tails and misconceptions and sometimes even legend that has nothing to do with what really happens in an engine. With that said, there are sometimes truths in some of those old wives tails, even if the reasoning behind them is faulty.
But what about port volume? Bigger must be better, because that is what every race head has going for it, right? But do those big heads hurt low speed power? You know, the power that gets you moving from a stop light? Or helps you accelerate easily on the freeway without burying your foot in it?
What’s interesting about this test here is that the test is being done on a variety of engines, not just one specific combination. Watch it and you will get some answers. But you might also have some questions. In fact, Richard himself poses a couple questions for you to answer in the comments and is probably setting himself up for a future test. But what’s the answer to bigger vs smaller?
Watch.
So the takeaway is that cubes make power, heads restrict power…? I.e., you can’t give an engine too much port volume but you can give it not enough port volume?
INTERESTING CLIP THE THINGS I THOUGHT I KNEW I DON’T KNOW THANK YOU
This test would be different with boost. The small stock intake port runs out of steam as boost levels increase (along with power levels). When running naturally aspirated as these tests were, good old atmospheric pressure – defined as 14.696psia at standard conditions of pressure and temperature, is the only thing “pushing” the intake charge past the valve and into the cylinder.. This does vary – but as far as an engine goes, not enough to make a difference. That helps to explain why a carb/intake combo that can handle up to 700hp is limited to minimal differences as shown in the tests here when changing the intake runner volume.