reduced compressor power and reduced charge heating ?
VLI will give the 'free supercharging' benefits over a much wider range of engine rpm
not only below 10500 rpm but also above 10500 rpm
these engines can and need to use a wider range of rpm with high or full demand from the driver
combined 'free supercharging' F1 mep gain from tuned length induction and exhaust systems was 35% (Merc) and 40% (last Cosworth)
tuned length induction systems should be rather useful to the current engines
tuned length exhausts may be less useful than in N/A engines ?
pulse reflections at points of geometrical expansion to atmospheric pressure are weaker relative to boost pressure
and current engines have much earlier exhaust valve closure than N/A race engines ?
as we're not allowed to have variable length exhaust systems
Last edited by Tommy Cookers on 19 Oct 2015, 13:45, edited 3 times in total.
Try to think of compressed charge air as a naturally aspirated engine with a higher pressure differential across the inlet on the induction stroke. This is a simplification as it doesn't take into account spool up and the increased charge pipe length, but for the purposes of the induction, the valve and trumpet behaviour it is not an unreasonable assumption.
The goal of Induction is to have 'good' gas mixing in the cylinder head and this is reliant on the trumpet velocity, which is in turn affected by the trumpet length. As the velocity of the flow in the trumpet will vary periodically with the intake stroke, their will also be a resonance wave that will establish across the trumpet. The resonance frequency is a function of the trumpet length amongst other things and thus can be tuned to match the intake frequency for a given RPM by varying its length.
The same philosophy applies to a compressed charge air vs a naturally aspirated charged air as the velocity of the inlets still vary with the engine speed, the main difference between the two is there is a higher pressure differential for a compressed charge which will drive a higher velocity and more gas molecules per unit area to perform combustion with.
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