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| floridacarlaws |
When the burnt gases move from primary pipes to collector, it creates turbulence across the junction where the area of cross-section changes.
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| verociousmotorsports |
Here I compare the dyno performance of the Chevy 302 engine after the exhaust manifolds are modified. If the exit diameter of primary pipe is closer to the inlet diameter of collector (right column), the engine gives a poor performance at low-rpm range because the collision between the exhaust gases coming from 4 channels is more vigorous. However, this design favors high-end performance because a narrower junction allows the burnt gases leaving the engine more effectively.
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| Measurement data |
The effect of junction turbulence is not obvious here. However, if you want to put your car on pole, it has to be taken into account.