Tmoss Porting



Is there a formula to determine plenum/runner size - for instance, to determine where you want your power at intake

It depends on your RPM range, Engine size and intended use of the engine. For instance, an engine utilizing an automatic transmission will have a much smaller plenum than an engine using a five speed. An engine with a five speed behind it can use another 20% more plenum volume. You must be careful here! The dynamics of the race track vary slightly from the dyno and in this regard, they vary a LOT! On the dyno you can tune an engine to produce max power by adding a considerable amount of plenum volume. In some cases you can almost double the volume and see a considerable power gain. On the track the engine will lag against the converter or worse yet, just not accelerate at all. Smaller engines are much more susceptible to this than larger engines. We know from extensive track tuning that our Pro Stock engines will not take any more plenum volume but on the dyno, I could add more volume and see more power. In this case, equations take a back seat to experience and practicality.

Your total intake runner volume (head and intake) to your cylinder swept volume should be from 78% to 96%. Depending on the rpm range you’re looking for.

Darrin Morgan

R&D-Cylinder Head Dept.

Reher-Morrison Racing Engines

|Engine Cubic Inches |Swept Volume |Swept cc |78% |96% |

|302 |37.75 |619 |483 |594 |

|327 |40.875 |670 |522 |643 |

|331 |41.375 |678 |529 |651 |

|347 |43.375 |711 |554 |682 |

|351 |43.875 |719 |561 |690 |

|377 |47.125 |772 |602 |741 |

|393 |49.125 |805 |628 |773 |

|408 |51 |836 |652 |802 |

|418 |52.25 |856 |668 |822 |

|427 |53.375 |875 |682 |840 |

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