[Diy_efi] : Ask the experts #2

[Craig Dotson]

>a) Do they work in practice?

Yep.  Dyno tuned a CBR F4i with several different runner lengths on a constant 
plenum volume and saw moving peaks in the volumetric efficiency (approximated 
with torque) very near predicted frequencies.

>c) When calculating the resonant frequency do you set the period based on a
>single inlet cycle or such that the pressure pulse comes back for the next
>valve opening?

For a 4cyl, 4-stroke engine tune for four times the intake cycle frequency, 
which corresponds to two times the engine speed you wish to tune for.  This is 
done because tuning for the fundamental mode would necessitate extraordinarily 
long runner lengths.  You lose some of the pressure increase, but you pick up 
another mode or two depending on your engine's operating speed range and tuned 
frequency.

Craig Dotson (digest)


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