Reply to "Strip Dominator on stock displacement engine"

> I had heard that the 4v intake port was designed for a 370 cubic inch engine.

A formula for the required minimum port area in square inches is:

Amin = (RPM * Stroke * Bore * Bore) / 190000

This formula is based upon the fact that volumetric eficiency stops increasing
at around a port velocity of 0.6 Mach.

If I did my math correctly, for a 7000 RPM 351C, that works out to 2.06 square
inches. A 4V intake port is approximately 2.5" tall by 1.75" wide which is
4.375 square inches. Under the valve seat, I've measured from 2.37 (untouched
with considerable casting flash) to 2.79 (cleaned up) square inches. Only a
small taper area is benficial so that huge mismatch doesn't help things.
I've got a set of C302B's from Alan Kulwickis shop from back when they were
making in the 750+ HP range with a flat tappet 358. The ports aren't terribly
large.

> I suppose my compensation for that is just to drive the car at a higher rpm?

While they work better the higher the RPM, they will still be oversized unless
your idea of higher RPM is Pro Stock territory.

> I did try a set of the B351 heads, cleaned up in the intake ports and found
> them disappointing. The A3s for my liking were right on it.

Heads are one part of a combination. Without knowing everything else about
the combination, you don't where to pin the blame. Perhaps the cam, intake,
headers or some other part you chose was better suited to the flow characteristics
of the A3's. Local circle track racers prefer the smaller port C302's to the
A3's because of the better throttle response. That's not to say the A3 isn't a
great cylinder. The 4V closed chamber head is a pretty good head, especially
on a larger displacement engine and the A3's are superior to the 4V's. In practice,
it often comes down to the particular head characteristics or the particular
combination of parts. I had planned to demonstrate this by testing several sets
of small and large port C302's and ported/unported A3's on my 403C but the dyno
is broken. It's not clear when the dyno will be back on line (repair parts no
longer available which required an upgrade and an adapter which is on back order)
nor when I'll be able to get back on it. If my white Pantera is ready before then,
that test will have to wait for another time.

> I do have a feeling though that the definition in this case for "optimizing" the
> ports has to do with total area under the curve and not necessarily peak HP, that
> might be where I felt the difference?

Possibly. If the engine made less power in the low and mid range, the
top end might feel stronger by comparison, even if it wasn't. The right size
ports work better across the RPM range but the difference is less as the RPM
increases.

> A little torque kill in the right parameters can be a good thing I think?

It will take a bunch of RPM before you get back to parity, much less make
better power if the head ports are considerably larger than they need to
be.

> So the Holley intake works by increasing port velocities on 4v engines?

No. The Strip Dominator has 4V ports.

> Wouldn't that intake need to be tuned to a specific camshaft profile to work?

It's always best if all the parts are tuned to the same range.

> presuming the ports mismatch to an A3 could be worked out, would it work
> on an A3 head too?

The Strip Dominator has 4V ports so you'd need to weld or epoxy the intake
manifold port floors.

> How much you want for that manifold?

Who are you asking?

Dan Jones