[zdkel]

For years, I have seen long narrow runners on engines designed for low end torque and short flowing runners on engines designed for high rev HP. I don't question that.

But can anyone explain why? Is it to do with the time available to fill the cylinder and how fast the air/fuel charge moves?

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[FordmanT]

[QUOTE=zdkel;3722054]For years, I have seen long narrow runners on engines designed for low end torque and short flowing runners on engines designed for high rev HP. I don't question that.

But can anyone explain why? Is it to do with the time available to fill the cylinder and how fast the air/fuel charge moves?

I believe you have that backwards, Usually tall intake runners are for high rpm applications such as drag and race motors so high hp. Short runners are generally better for more torque since they help make power at lower rpms, generally speaking this is where an engine will make it's peak torque. All has to do with flow distribution. Old carburetored engines are not street friendly (unless you drive like your at the track) with single plan intakes or tall (sometimes called ram-jet) intakes since the engine is trying to pull air/fuel in equal to the entire volume of the entire intake. So at low rpms the engine will run rich because it cannot effectively draw in the needed air to match the fuel it receives until very high rpm. Where as with a dual plan intake, even though it isn't completely blocked off side to side typically, each cylinder only has to attempt to draw the air/fuel mixture in from half the intake. Same idea carry's over to the tall and short intake runners. When an engine is turning high rpm (6500+) each cylinder needs this volume available to attempt to draw in the maxim amount of air/fuel per cycle since it only has a fraction of a second to do so. Hope this helps