>Subject: [alfa] Re: Porting in general...

[RonHorowitz <RonHorowitz@xxxxxxxxxxxxxx>]

Erik, et al.,

>
>Ah, Ron, to disagree, part of the essense of the Digest.

So it would seem....

>To consider porting without thinking of the cams is a big mistake.

To think the cams come first is a bigger one. Displacement and RPM yield
target CFM, thus target port cross-section, and target valve sizes. It's
iterative, but the cams are chosen to suit the balance of the metal, not
vice versa.

>If you port
>the intake to give you great momentum dynamics at, say, 7000 rpm, and you
put
>cams in the engine that have short duration and low overlap, the car will
not
>perform well at all.

I think we should start off by defining "great momentum dynamics," but be
that as it may, if you have a port with _great_ momentum and an
inappropriate cam, it will peform far better than an engine with _poor_
momentum and an inappropriate cam.  Also, I suspect you may be confusing
resonance, another can of worms, with momentum.

>The point of the cam timing is to take advantage of the momentum 1) while
the
>valve is still open,

It should be obvious that no air flows when the valves are closed. The
example of high velocity gasses slamming into a closed valve is the
limiting case.

>and to a lesser extent 2) when there is overlap.

On an Alfa, or any of the typically crappy Italian cross-flow hemi-heads,
high-momentum and high-overlap aren't fully compatible. Get the intake
screaming into the chamber while the exhaust valve is open and it'll just
keep screaming right on back out the exhaust. Take my word for it, try it
for yourself. or refer to Sir Isaac Newton, but you can see what I mean.

>If you
>port the head for high momentum, you will need cams that close rather
late, so
>that the pressure in the intake is higher than the combustion chamber even
>while the piston travels back up.

Nonesense. You are confused. Think about what I'm saying, not about what
you're thinking. If you port the head for higher momentum at _the_same_
CFM_, you don't need high-duration, late-closing, or any of that. Get the
ports to breath, and you don't have to leave them open all day. Not to
mention you'll have natural anti-reversion due to high momentum.

>But lets say I port the head to flow freely, to minimize the restrictions,
and I
>use shorter duration cams, I could say that even with the lower momentum,
I can

Again, you are confusing free-flow, minimum-restriction, and low-velocity.
If you can get _exactly_ the same CFM at either high or low velocity, you
will _always_ have a better result with higher velocity. Raising the
velocity while retaining the required CFM is the practical goal of
performance porting. If you don't get that, you don't get that, but if
you'll think about it for a minute, you will.

>put the same charge in at the high rpm assuming I also properly match the
lift.
> One is about using the momentum to put the charge in, the other is about
>minimizing the restriction.  Can one do both at the same time?

This is exactly what I'm talking about. The Kartamalakis port design
unecessarily slows the gasses in order to reach his CFM target. He gives up
more momentum than in required to achieve _the_same CFM.

>Sure- but I
>would not want to drive it on a car with limited gear ratios...

You are either confused or inexperienced. You get the velocity up while
delivering the CFM and you have an engine with a broad, flat torque curve.
You "hog out the ports" with a sub-optimal geometry because you don't know
any other way to get the CFM up, and you get an unecessarily peaky power
band.

>The nice thing about my short duration cams is that at the lower rpms,
where one
>can not use the momentum as well, I still have a high charge.  Which is
really
>increasing the area under the power curve.

Ay, carumba....

>It is a SYSTEM, one can not cam without thinking of the ports, and one can
not
>port without thinking of the cams.  You can not optimize one wihtout the
>other.

No one said otherwise. What I said was that a high velocity port is better.
You are confused in that you equate high velocity with low CFM. These are
not synonyms.

>Also, I don't see how I contradicted myself when I mentioned that all CFD
models
>have problems modeling exhuast revision.

You are missing the point. You contradicted yourself about the benefits of
high velocity versus valve events, i.e.,:

>>Especially all the back flow from the combustion gasses into
>>the intake when the valve first opens, during overlap.

Think about it.

> I've never known port flow to be
>steady, ever- there is nothing steady about it.

Beside the point, and no one said it was. Quasi-steady-state measurements
are about as good as you're likely to get. If you know what you're reading,
the data you get on a quasi-steady-state flow bench correlates extremely
well to the practical realities of power production _regardless_ of the
time variences. This is why every race engine buider worth his salt has a
flow bench. It's why Superflow and all the rest are in business. This isn't
snake oil, it's the way the things are done.

Besides, you're getting off the subject.

>Again, Ron, unless you've actually done the research, one can not blanket
say
>that Jim K's book won't work.

I didn't say that the Kartamalakis _book_ wouldn't work, I said that his
_port_design_was NFG. The port design is sub-optimal. I don't need to ruin
a perfectly good head to figure that out.

>Considering who it is, I'm fairly sure he has
>done the work,

Considering who I am, (whatever the hell that's supposed to mean,) I'm
fairly sure he didn't do a very good job with the ports. Maybe if you see
the data, you'll understand. OK, so here's a constructive offer to put this
issue to rest.  Get me a Kartamalakis ported head and I'll flow bench test
one of his intake and an exhaust  ports _for_ free_. You'll see what I mean
when you see the numbers.

I'm out of town building race cars for the next few days, but email me off
the digest if you're interested.

RON
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