There's more to it than just the momentum (inertia) of the air in the stack.
Way back in 1960 I wrote a student engineering paper on ram induction after
Stu Hilborn, Leo Goosen (of Meyer Drake/Offy),GM, and Chrysler all kindly
responded with lots of info and photos after I asked them about the subject.
The 1960s Chrysler ram induction used inertia, but the main point was that
the combined ram tube plus port length was selected such that the natural
frequency of the compressable air in the "tube" was reinforced by the intake
valve frequency. This acoustical "tuning" created a resonance condition that
boosted the pressure at intake valve opening above that available from the
inertia effects alone. For the long tube Chrysler manifolds, Chrysler
claimed a torque boost of 10% at 2800 RPM selected design point (with some
torque boost over a 1500 RPM range) for the ram tubes compared to a
"standard" manifold, so their claim included both the increased inertia plus
the resonance tuning effect. They actually lost some torque below 1200 RPM.
The tuning effect can be designed for a peak torque boost at any given RPM
and a higher RPM design point was selected by Hilborn/Chrysler for the
destroked Hemi powered Kurtis Roadster that they tried at INDY in 1953.
My 1960 paper has a lot of stuff on the inertia/resonance effects (suprised
this old man taking a look at it now!) and has some qualitative road
test/drag strip comparisons between two 59 and 60 Dodges--the only
difference between the cars was the ram induction manifold on the 1960. If
anyone wants a copy of the paper, let me know and I'll try to scan/email it.
Lance
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Tom, Redding CA wrote:
> If you remember the Ram Induction that Chysler was using in the early
> 60s, you will note that their design was changed from the original long
> rams to shorter ones for high performance engines. The long runners gave
> gobs of torque in the lower rpms, but sacrificed hp on the top. The
> shorter runners moved the torque up the rpm scale. The idea behind this
> system was to use the momentum of the air movement to stack air against
> the intake valve while closed. This gave a more dense charge when the
> valve opened.
>
> Tom, Redding CA - #216 D/CC
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