Tapered intakes, port velocities etc.

[Beaubien, Matthew]

Fred (& Todd),

. Thanks for posting the article. I for one found it very interesting.
. Haven't seen any discussion on it, so I wanted you to know at least
one
. person appreciated the time you took to type it in.

I'll second that. It really gave some food for thought. Recently, I've
been helping a friend build a flow bench and we had discussed some of
what was mentioned in the article.

One "rule" about flowing heads is that you want as much low-lift flow as
possible. I never came across any reasoning behind the statement. The
way I saw it was that you have the smallest pressure differential when
the valve is first opening, and thus, the least potential to flow a/f.
What I didn't take into consideration was the flow through the valve
while it was closing, when the interia of the a/f mixture is probably
close to its maximum. It sounds like a large part of the cylinder
filling may happen when the valve is closing/near closed.

Am I on the right track?

Todd, you mentioned the velocities seemed high compared to what you work
with. You mainly work on turbo flat 6's, correct? The article seemed to
be more bike orientated (obviously) which would mean multivalve engines
that spin about twice as fast as your used to. I would assume those
factors would have some bearing in the velocities. However, the pressure
differential you're dealing with is greater (ie. turbo boost) which
should speed things up. When talking about velocities, are they measured
or calculated? Don't hold me to any observations as I haven't taken
fluids yet ;-).

Does anyone know of any good SAE articles on manifold/port/valve design?
I remember reading a good one by GM on their Vortec engines where they
gave some good real-world data (ie. dyno graphs) of various port
configurations (mainly size). I believe there was some info on the
manifold design they chose and why (it had the widest torque curve if I
remember correctly).

Interesting stuff. I just hope we don't have another "blood-letting"
with a DIY-EFD (engine fluid dynamics) group
forming ;-). Maybe I'm wrong and there would be enough interest/support
for it.

Comments?

Matt Beaubien
mbeaubie at gpu.srv.ualberta.ca
3 '71 Datsun 510's (one turboed on M85), 1 1.3L '77 Civic 1200