Reply to "Strip Dominator on stock displacement engine"

> Notice he wrote his 351C 4V pulls hard all the way and never stumbles.
> A 351C 4V with throttle response described as pulling hard!

Hard is relative.

> The ports are too big my arse!!

For most uses, including the power levels that you advocate for the street,
the ports would work better if they were smaller. Larger ports mean slower
velocity and slower intake flow port flow is more susceptible to reversion.
Momentum is the product of mass and velocity. If the velocity is low, the
momentum is low and may not be able to overcome the rise in pressure that
occurs when the intake valve closes which allows reversion flow (from the
cylinder back into the intake tract). A low air speed also implies a weak
pressure wave action (and subsequently weak resonant tuning).

There are waves that travel the length of the intake tract. The frequency
of these waves are a function of the runner length and cross-sectional area.
Note that these waves move within the intake (and exhaust) flow. Depending
upon their direction, they can either aid or hinder flow motion. One
characteristic of an finite amplitude wave is that when it hits an abrupt
area change (such as a runner opening into the plenum in an intake manifold
or a primary pipe ending in a header collector), it will change direction.
So an expansion wave moving up the intake tract will change direction when
it comes to the plenum opening changes and become a compression wave heading
towards the intake valve. By timing (via the valve opening events, intake
runner length and cross-sectional area, header lengths and diameters) the
waves can aid in cylinder filling on the intake side and cylinder evacuation
on the exhaust side. Get these events right and you can certainly have
volumetric efficiencies of over 100%, especially near peak torque but also
near peak power.

There's a reason Engine Masters competitors like Kaase and Storlien shrink
the ports of their heads to match the RPM range and displacement. There's
also a reason why Ford engineers made the ports smaller from 4V to A3 to B351
to C302. For a given engine configuration, it is reasonable to assume there
is an optimal timing of the wave harmonics which would also determine an
optimal runner cross-sectional area and length which imply an optimal velocity.
This cross-sectional area would only be optimal for one RPM and perhaps its
harmonics so picking the area needs is a compromise for the RPM range desired.

Dan Jones