01-08-2020, 11:56 PM
For an inline four with a standard firing order (no cross-plane trickery with the crank), the 4 into 1 provides the most efficient exhaust scavenging. The pressure pulses of exhaust gases travelling down the pipes at regular intervals creates a venturi effect at the collector which helps draw the last of the spent gases out of a cylinder that is completing an exhaust stroke. An optimally designed system will be a bit more efficient and/or powerful over a given rpm range.
As a bonus, a 4 into 1 has less mass than a comparable 4 into 2 system made of similar materials.
For turbo or supercharged engines, this is not a concern. The boosted intake charge blows the spent gasses out during the short valve overlap that occurs at TDC. In such engines, the individual pipes don't even need to be joined as no scavenging is needed.
See this excellent video:
https://www.youtube.com/watch?v=m2hZql6tD7c
As a bonus, a 4 into 1 has less mass than a comparable 4 into 2 system made of similar materials.
For turbo or supercharged engines, this is not a concern. The boosted intake charge blows the spent gasses out during the short valve overlap that occurs at TDC. In such engines, the individual pipes don't even need to be joined as no scavenging is needed.
See this excellent video:
https://www.youtube.com/watch?v=m2hZql6tD7c