Engine intake runner length?

  • #1
I'm currently adapting a rack of four 36mm carbs to a 1.6L (97.64 ci) 4 cylinder engine. I'm trying to figure out how to calculate the proper intake runner length to use. This is to be a zippy daily driver, not an 1/8th mile drag car. I've found information on "Independant Throttle Bodies" length calculations for fuel injected systems, but this involves a plenum and does not seem relevant. Any help would be much appreciated.:smile:
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  • #2
I can't help with any formulae. As a general rule, however, your power band is partially governed by the runner length. Longer means your band is in a higher rpm range.
  • #3
As far as I know the whole secret of side draught carbs are in the fact that they have very short intake manifolds producing power from a very low rpm. range. part of the m3 power is the 6 individual throttle bodies mounted directly on to the engine. Suggest you make the runners as short as possible.

1. What is engine intake runner length?

Engine intake runner length refers to the distance between the engine intake valve and the point where the air and fuel mixture enters the intake manifold. It is an important factor in determining the performance and efficiency of an engine.

2. How does engine intake runner length affect engine performance?

The length of the intake runner affects the velocity and pressure of the air and fuel mixture entering the engine. A longer runner length allows for more time for the air and fuel to mix, resulting in increased torque at lower RPMs. A shorter runner length allows for quicker airflow, resulting in higher RPM power.

3. Can intake runner length be adjusted?

Yes, intake runner length can be adjusted through the use of variable-length intake manifolds. These manifolds have adjustable flaps or valves that can change the length of the runners based on engine speed and load.

4. What are the advantages of a longer intake runner length?

A longer intake runner length can improve low-end torque, resulting in better acceleration and drivability. It can also improve fuel economy by allowing for a more complete combustion of the air and fuel mixture.

5. Are there any downsides to a longer intake runner length?

While a longer intake runner length can provide benefits in low-end torque and fuel economy, it can also limit the engine's high-end power and performance. This is because a longer runner length slows down the airflow, resulting in less air and fuel entering the engine at higher RPMs.

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