perf-list-digest Friday, July 24 1998 Volume 01 : Number 039

Ford Truck Enthusiasts - Performance
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In this issue:

FTE Perf - Mixture
Re:FTE Perf - Race truck update
FTE Perf - Mixture & Runners
Re: FTE Perf - Re:Laminar flow
FTE Perf - LONG Re:Laminar flow
FTE Perf - building a 400



Date: Thu, 23 Jul 1998 06:50:50 -0500
From: (William L Ballinger)
Subject: FTE Perf - Mixture

> George and CS bring up an interesting points which also, seems to me,
> introduces the concept of correct mixture. There is a difference in
> physics
> between suspension (atomization is a better word) and vaporization. Smoke
> is a suspension of solid in a gas. Gasoline vaporizes in air and loses
> all
> liquid characteristics. It is no longer "wet" until the air is saturated
> and can no longer "hold" any more vapor. Vaporization, in physics, is a
> change in "energy state". CS is correct-- you have to heat something to
> vaporize it. The heat drives the molecules in the liquid to move faster
> and away from each other and when they lose contact, that is vaporization.

Do you really vaporize the mixture though when you move it in air
suspension? A diesel would, once the mixture reaches the chamber and is
compressesed, the mixture by virtue of the ambient heat and friction of
the molecules bouncing off of one another's similarly charged fields
then becomes a mixture that can spontaniously combust. Vaporization
would then be that little transient state between atomization and
combustion. Gasoline would have also have this state, though to a lesser
degree in its own combustible state without spark applied, but would
reach it fully when spark is applied the moment before the mixture

Atomization on the other hand requires that the mixture be kept in a
state that keeps the droplets small but not so small that they
vaporize. This is accomplished by moving the air/fuel through a
pressurized tunnel with sufficient velocity that atmospheric pressure
can keep the mixture in suspension. Once the mixture vaporizes it is in
it's most volitile state, shedding it's combustilility into the
atmosphere at a much quicker rate than if it's only atomized. If it's
burned, it's then converted to thermal

Summing up, wouldn't atomization describe the mixture in it's state up
to being fully compressed, and vaporization the moment right before
- --
Come on over to my Back Porch
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Date: Thu, 23 Jul 1998 10:14:20 -0500
From: "KKM"
Subject: Re:FTE Perf - Race truck update

Hey Brett,
Do they allow a larger MAF change by the rules, the unit on '92 and larger
should be more suited to your needs. Also if your are running the stock
EEC, you should consider an A/F Ratio Monitor, as the 2.3L runs hog rich
under open loop conditions, which is where you would be 95% of the time.
You could effectively override this condition with an adjustable fuel
pressure regulator and an altered MAF voltage output signal to the EEC.

By the way, what part of the country are these IT events taking place.

Warren Kurtz
Kurtz Kustomz Motorsports

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Date: Thu, 23 Jul 1998 16:35:38 -0700
From: "George"
Subject: FTE Perf - Mixture & Runners

I've always read the plugs to find out out where I'm at with air/fuel
mixture. The big boys use some neat gizmos to read their plugs and usually,
on normally aspirated gas/alcohol race cars, run different jets in each
corner of the carb to compensate for different runner lengths or different
degrees of bends in the runners, atmospheric conditions and those other
tricks that shave fractions of a second off performance times. That reminds
me that, unless it's a ram manifold, a lot of different things can happen to
that mixture during it's travels. The ram tunnel manifolds are fine for
those who live in 5 grand rpm and up worlds.

Those who know their physics tout that a smooth interior runner provides the
fastest and most efficient route for the mixture to reach the combustion
chamber. That sounds good to me until I think about that route being a stop
and go situation, and in a street engine that usually includes at least one
turn from the top of the runner to the combustion chamber.

Others who also know their physics and build racing engines favor a not so
smooth inner runner. They feel that the stop and go mixture travel is aided
in retaining it's ideal consistency by turbulence created by the not so
smooth walls.

Additional information states that certain race manifolds are being cast
with dimples in the inner runner. That boggles my mind when I think about
the cost of a very limited production casting as complicated as a manifold,
and makes me lean towards the turbulence theory.

At least I didn't fall for the Splitfires or Like New Engine Additives, so
perhaps there's hope for me as I attempt to beat this thread into the ground
trying to find the absolute answer. If there is one.

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Date: Thu, 23 Jul 1998 19:26:08 -0700
From: "George"
Subject: Re: FTE Perf - Re:Laminar flow

Has anybody talked to a manifold manufacturer on smooth/textured runners?

George Miller

some of the fuel is vaporized. some of the fuel is in droplets, suspended
in the air column. not all of the fuel is vapor. and, to complicate
matters different fuels have different charactoristic as to how much will
turn to vapor. for example, turbo blue race gas when run in my four
wheeler will cool the carb so much that it will freeze in cold weather, and
have ice on it in hot weather. pump gas does not do anything - the carb
remains hot all the time. i attribute this to that fuels' ability to
vaporize well/quickly. this is also VERY noticable on my friends pull
truck - the carb stays cool even after a WFO run on the track. (BTW-this
fuel does require rejetting for max performance!!.)

so, since not all fuel is vapor, surface texture does matter. Sometimes,
it is arguable, you want droplets entering the chamber, and vaporizing
there, as the same mass of fuel takes up more volume vaporized than as a
homogenious (correct term?) mixture of suspended fuel droplets. so, in
this situation, the mixture can be richened up as more air is pumped into
the chamber. but, the other side is that as vaporization occurs, the
charge is cooled, and at some point will also increase the total amount of
air into the chamber (note: this is one reason alchohol makes more power,
the other is its richer a/f ratio.).

gets complicated doesn't it.


- ----------
From: Neal B. Forbes[]
Sent: Wednesday, July 22, 1998 12:51 PM
Subject: FTE Perf - Re:Laminar flow

major snippage - see previous post!

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Date: Thu, 23 Jul 1998 22:16:47 -0700
From: "Chris Samuel"
Subject: FTE Perf - LONG Re:Laminar flow

Date: Wed, 22 Jul 1998 12:51:39 -0400
From: "Neal B. Forbes"
Subject: FTE Perf - Re:Laminar flow

- -> Rivers of gas in an intake manifold are a problem of
- ->carburetion, not internal texture. The carb jets simply spray (atomize)
- ->liquid gasoline into a moving air stream to assist the process of
- ->vaporization.

Would that this were only true. The texture of the internal surfaces has a
whole bunch to do with the rivers of fuel, even on MPEFI. Not only that, the
poursness(is that a word?) has an effect. I was talking about this subject
with one of the horsepower developers I know (30+ years of dyno time) once;
and was asking about the texture issues. Seems that they once tried coating
the inside of the manifold with a thermal barrier on a race engine; the idea
being to keep the mixture cold. Well the end result was that the engine had
a ton of fuel distribution problems. The only thing that changed was the
coating. It was the exact same manifold.

- ->So, CS, IMHO the discussion about significance of the internal texture of
- ->intake runner should center around the ease of movement of the charge from
- ->the carb to the chamber.

Yes, but, we are not dealing with just a dry or wet situation and when you
have the mixture you have to change the approach a bunch. There are things
that you do to enhance one that will totally disrupt the other. and we have
a mixture of the two! Oh Fun!)

- ->Incidentally, air in the boundary layer moves more
- ->slowly than the air above it because it contacts to wall and is slowed
- ->by friction. Smoother textures make less turbulence in the boundary layer
- ->which makes slicker flow with less work.

True. No Question.

- ->The tendency of condensed fuel to revaporize near the port is because it
- ->hotter there.

Not completely True. The fuel will not pick up enough heat in this area to
make much of a difference (compared to the "Hot Spot" in the Plenum). The
speed at which it is moving is too great. Consider that the A/F mixture will
go past the sonic threshold as it moves through the throat or pocket area
just above the valve. Yes you read that correctly, supersonic speed. Why is
one of the critical things to know the Mach Number for the port? Most
engines like to be under 0.3 Mach as the aggregate number.
Bunkum and Hogwash you say??? well then try this one out...
What is it that makes the noise that you hear at the end of the exhaust
pipe? You know that loud crackling noise that you get with open headers?
The sound of the vary rapid oxidization to the air fuel mixture???
No, no, no... you can not hear that because the valves had darn well better
be closed during that time! Sooo... all of that noise is contained inside a
metal container, not much sound there.
It is the sound of the exhaust gases breaking the sound barrier as it
escapes past the Valve.
If it were not for the speed that the intake charge reaches the injectors on
the MPEFI would have to be much higher in the system because they don't
break the fuel into good droplet size at pressures under 85-90 PSIG. But
smack that fuel with a shock wave and presto smaller droplets!
Next you must add in the reversals that take place when the valve closes.
These pulses are strong enough to blow fuel out the top of the Carb and
through the Throttle Body on a MPEFI system. Cool. That "DRY" intake system
that we were lead to believe "Tuned Ports" would give is just another
"Marketing Myth".
A "correctly mixed" charge in a normal engine is a mixture of air and liquid
fuel in vary fine droplet form.

- ->But a correctly mixted charge has no liquid to start with.

Not True.
As you pointed out a vapor is simply a molecularly spread out liquid. A
spread out fuel takes up more space (volume).
So to get X number of BTU out of X weight of liquid fuel you have volume X
and 14 parts of air.
But vaporize that volume X of fuel and you have to take in 10X Volume (due
to expansion) AND the original 14 parts of air.
You have to take in more. But you can only take in so much for any given set
of parameter. To make the most power you must take in the most of the
correct mixture that you can(Ok I am getting redundant).
Nothing fancy here Max power is made with:
Cold: and therefore dense dry Air.
Fuel: in the smallest droplet size possible, preferably cold in theory,
At a ratio of +/- 12.5:1 give or take a little.
The air fuel well homogenized and packed into the cylinder in this form
until the valves are closed. Then all of the fuel breaking to vapor just
before the spark occurs.

- ->We could go on to the geometry of runners and talk about straight vs.
- ->single vs. gang, single plane vs dual and on and on. But all changes in
- ->geometry are after the same goal--reduce the turbulence by straightening
- ->path of the charge from the carb to the chamber, and isolate each
- ->feed so that that chamber does only the work it needs and not another
- ->chamber's work. An eight runner tunnel ram is the epitome of an intake
- ->manifold and approaches the concept of a header.

Straight VS Bent No Diff if the Radius is big enough.
Single planes make more power under the curve when properly set up. Period.
My Opinion. Sleddog's Opinion, The Dyno's Opinion. and...
See CamaroCraft this month.
OUCH! That Hurt! A correct bit of Info in a Peterson Magazine!
Both Plenum's and Collectors easily make power, anything else can but it's
hard and may not!
Port walls should taper 7 away from the valve. That is Port Geometry.
A tunnel ram will make the most power of any intake manifold. But... It can
be hard to see past on the Street Strip or Trail:-(

- ->We could also have a great discussion of the mixture but that needs to
- ->encompass the carburetor and all the cool things about them. So CS, now
- ->can talk about the desirability of supplying correct mixtures to the
- ->manifold and how that effects performance.

OOP's I just did... Sorry


And I cut this...

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Date: Thu, 23 Jul 1998 22:24:46 -0700
From: "Chris Samuel"
Subject: FTE Perf - building a 400

One of the big fears many M-block owners have about higher compression
ratios is the pinging problem. So far, in the M-block engines that I've
built w/ higher compression ratios, the pinging is no worse than w/ the
stock low compression engine, and in some cases the pinging actually seems
to be less of a problem. The last 400 I worked on w/ about 9.4:1
compression pings less than my stock 351M w/ 8.0:1 CR. Go figure.

Dave R. (M-block devotee)

Was the engine fresh or fresher then yours?
Easily could have been oil control. I.E.. Better.

As a general rule I only recommend 9.5:1 on these engines as it allows
getting some occasional bad gas with out hurting anything.
If you are only running a 50/50 mix of Av Gas & Prem. Pump go to 11.0:1 and
make some power, or 14:1 or more on Alky.


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