The real basics

[Bruce]

For quit some time, I've been getting mail about where to really begin with
EFI.

So here's my notes, and opinions on things. Your results my vary some, but
there is alot of time spent in accumulating this info.. If you wan to
haggle over it, that's fine, but I'm probably not going to be the one to
haggle with. Unlike the talking heads that write magazine articles, every
item of info here is from actual testing, and analysing results. Some
explainations are simplistic, since this isn't a design course. What
matters is what works.

Mixing the fuel:
Fuel is made into a reactionable state thru atomization, and or
vaporization. The net result is the same, but manifolding and the type of
EFI to maximize the results differ greatly.

Atomization:
In this case the fuel is mechanically shredded, into fine particles.
It's how carburetors and TBIs (to a large extent) both work. In the TBI
it's just the venturis, and emulsions tube jobs that are replaced with
Injectors and electrons. The carb has the atomization taking place in the
venturi, and the TBI has it taking place at the edges of the Butterfly.
It works out exactly the same for WOT and MPG. The two advantages for EFI
are cold
starts, and fuel sloush. Both have *wet* manifolds, and for that reason
are, usually hard to compare back to back, but using a Cross Fire lower
manifold and a custom lid for a Q Jet, the results were the same as far as
in the test car running mid 13s, and 27 MPG. The down side is at WOT the
fuel just flows past the butterfly, with min atomiziing. So at higher
speeds, you have to use some vaporization to keep the fuel in a suspended
state. If you relly look at some of the TBI manifolds they are very clever
in what the do. ie., on some they take the heater water out of the back of
the manifold, so in warmer weather the coolant flow thru the manifold for
the heater is min., so in the winter the manifold runs alot warmer. What
I did was run without a heater valve, so that there was always some coolant
running to help vaporize the fuel. In order to make it most uniform in
temp., I did block off oil reaching it, with a lifter valley pan. Also,
ran a 180dF thermostat. This allowed for the best combo of cold hot, high
low rpm drivibility. Everything has it's trade offs.
The wet manifold has some issues that you want to consider. There is an
optimum range for air speed thru it. Too slow and the fuel falls out of
suspension, and too high, and it *sticks* to all the runners, where they
bend. If the manifold doesn't have not enough heat, or wrong plenum volume
you can
also wind up with the fuel traveling in rivers along the base of the plenum.
These details are not to be ignored. First, thing most guys think is that
more air cleaner is better. Nope, it can drop the air velocity down low
enough that the fuel is puddling, and not in a good state for reacting in
the chamber.

Vaporization:
This is where heat is used to evaporate the fuel so that it can be reactable
with air in the combustion chamber. On your TPI type systems the fuel is
just sprayed on the back of the intake valve (well kinda sorta near it) and
then just waits around boiling til the valve opens. SEFI can really help
this process at idle and low rpm, but very low in the rpm range the
advantage is lost. So for a real HiPo engine it can help, that's about the
only reason for it. In the real world of new car sales, it does
matter since they are selling millions of cars and each lil bit helps with
CAFE etc., but in our world you'll not likely see any big difference, till
you get to the large injector area.
With the injectors close to the port the manifold is rather dry, so air
speed tends to be more flexible, since fuel falling out of suspension isn't
such a big deal. BUT, what can be an issue is the runner tuning, to cover
the low speed problem of not enough heat to really boil the fuel. So the
engineers made the compromise of using the runner lenght to really enhance
the low speed cylinder filling.
Also, turbo really like this, since at serious boost levels the air temp is
elevated and boils the fuel nicey (all things being relative).
There is a real problem with TPI and vaporization at high rpm. The
later LT1s, LS1s, have really a well designed system, and in all honesty are
far better then the earlier TPIs. But, again, the TPIs have a fairly nice
series of ecms that can be tuned to min., their short comings.

Matching Components:
Contrary to lots of info., the only hot set up involves testing what your
engine likes. No dyno, or part that looks right means much when the green
flag drops. Testing, testing, testing. Do what the engine tells you it
likes. On some extensive testing, I found a 2.25x14 K+N to be faster then
a 3x, or 4x, and that was optimizing the fuel and timing to within 1%, and
1degree.
If you want ram air, there are two considerations, the volume of the
ducts, and the actual air intake. The ducts seem to work best at equalling
the engine displacement. For it to be real ram air the intake must extend
forward of the sheetmetal by several inches, or the scoop several inches
above the hood line. The Mopar Chassis Book has some good notes on this.
Just as an honorable is cowl induction. I will alow the engine
compartment to vent hot air when standing still, and the as speed raises,
force air into the engine compartment. You can run into some weird cooling
problems, if you soon't understand that the cowl induction is great at
filling the low pressure area under the hood, and that mins airflow thru the
radiator.
Also, remember, that all the airflow bench flow testing is done steady
state, and that just doesn't happen in the real world. Lil airfoils and
such might show a gain on a flow bench and do nothing for an actual engine.
And at some time or another there is reversion, which can be a good thing or
at least managed, that Never shows on a flow bench.

Operating temps.:
No reason for running less then 180, and personally I get best results
with 190dF. Thing most people ignore is oil temps., and that has alot to
do with the actual piston temp....... Some claim better resistance to
detonation, well I can run 3d more timing then peak HP, in my turbo car, and
we'll just say it runs quick. Using a low temp thermostat to control oil
temps to some degree just don't make sense to me.


General Conclusions:
In stock form,
TBI, is for the lower rpm range engines.
TPI, does about the same, but has slightly better metering.

Modified,
They both can do a really grand job if you maximise their strong points,
and min the weaker points.
TBI, you want to use a well thought out manifold. Single plane is best.
You need to run some controlled amount of manifold heat, for High RPM
useage, since you lose the atomization advantage there. No real need in
trying to run a TBI off of a TPI ecm, BTDT. You want the faster pulsing
rates to help with the atomization.
TPI, bigger plenums, shorter runners (or at lest shared runners). You
want textured runners for the increase in surface area. Since they are
basically dry you can get by with a smaller runner manifold for the same HP
level as a TBI.

Detonation:
It occurs in the chamber. First thing to work on is getting the chamber
right. Min., it surface area, and for heavens sake radius the chamber to
cylinder head surface edges, just .01" or so but you should be able to rub
yourfinger all around the chamber and not draw blood...
Want to run 11:1 CR?, Fine, just be sure to have a late closing intake
valve.
The less timing needed the better, 76cc heads WOT 36idh degrees, 64s
34ish, 56 AL 28ish. Again the less the total timing for a given level of
HP the better. Plug gap can reduce the amount needed to, just it's hard on
ignition components.

Thinking:
If it works it works, ain't no more difficult then that.
Reading plugs is necessary, period. Like it or not, they are the eyes
into the combustion chamber.
Experimenting without a base line is just wasting gas.
Be honest with yourself.
Do what you can afford to do.
Don't think cause something worked on your car that it's a universal
truth.
If you think your going get recalibrating a car right for the first time
in 100-200 chips, your just wishing aloud. There are a million combinations
for what may work.



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