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Plenum and collector: a symbiotic relationship ?

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Hello all,

I have question, in a naturally aspirated engine with fuel injection, is the relationship between plenum and collector size a symbiotic relationship? I.E. if I make my plenum larger does it effect my optimum collector length? Does anyone know any resources or books/videos that touch this subject?

Thanks to all, stay safe.


Hello Scott,

as far as te testing I have done over the years I have found no relationship to support this theory I have heard of it but never once noted it during dyno testing, I would also be interested to know what others have found

Both of those are just part of their associated systems, the intake and the exhaust. In theory, as Ross said, any change in the gas flow on one side 'should' affect the other, but there are a lot of other factors involved and, unless there is a big, negative, affect that's caused or cured, things like runner/pipe lengths and diameters may be expected to be more critical.

I know there are formulae for all parts of both systems, and by optimising them, and other aspects of the engine, the ACTUAL VE of the engine can be well above 100% - in NA form racing four stroke engines have approached, and may since have surpassed, 150%!

You could do worse than pick up and read this seminal work on the subject - https://www.amazon.com/Scientific-Exhaust-Systems-Engineering-Performance/dp/0837603099

Failing that, there are many good on-line resources.

So what I am understanding the actual design of the structures are more important than the relationship between the two. OK. Since my engine is a little bit odd. It's a 07k 5 cylinder (volkswagen) port injected. The 07k is an under-square engine and has the overlap of firing events Making it even more efficient (I suppose) could this relationship be more important than in a traditional 4,6 or 8 cylinder.? Also, any suggestions for 5 cylinder info /tuning Advice? The vw forums tend to be hit or miss, mostly miss.

Thanks guys,

Stay safe


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