I still monitor this group when I have a minute, and there is only so much
misinformation that any engineer can stand..
so here goes..
mechanical injection,constant flow
fuel pressure variable with rpm change the pump drive speed to bring in more
fuel on the top end. It makes a steeper curve from idle to WOT pressure
Main bypass drops fuel pressure to change the height of the fuel pressure curve
and maintain the slope set this bypass for correct air/fuel ratio at peak
torque.
then readjust the barrel valve for best idle with no stumble. When you find this
value use your leak down tester to get the value and later reset it if you have
to disassemble the unit.
Secondary bypass spring loaded for activation at a certain fuel pressure, drops
fuel pressure for peak hp. The rpm input for this is pump pressure. plug this
while setting main bypass for peak torque. Use your leak down tester to set the
spring opening point to start at the fuel pressure that corresponds to the
beginning of the torque drop off after peak torque. ex. if peak torque is at
6500 then whatever the fuel pressure is at 6700 should just barely crack the
bypass,shim spring as necessary to get this right. adjust the jet for this
bypass for best air fuel ratio at peak power, you may have to go back and forth
a few times with the jet size and spring tension. This is basically a high end
lean out that is controlled to get the fuel flow curve to match the torque curve
from peak torque to peak power.
Boost compensation, there are diaphragm type units for boost compensation that
basically close off the main bypass and raise pump pressure according to boost,
used mostly on a turbo application as a mechanical supercharger has a basically
linear boost output with rpm and can be described well enough with the standard
main and secondary bypass. The turbo is load related as far as boost is
concerned so you need the diaphragm, it is expensive and cumbersome to work with
but about the only way to do this..
Mechanical injection timed, lucas style
Pump pressure is constant(last I looked it has been a very long time since I
played with one of these) many use electric pumps or small mechanical ones.
fuel is timed to the cylinder, i.e. a v-8 has a 8 output distributor and a 6 has
a 6 output etc.. Phasing is adjusted by setting the position of the metering
unit the same as a ignition distributor. once set it is fixed.
Fuel for throttle position is adjusted by the pump cam in the metering unit.
most any shape that can be machined can be used...fuel for rpm is adjusted by
the metering unit as well.
Much more accurate than the hilborn constant leak system.
If you have either of these two systems your best source of parts and tech help
is Kinsler Fuel Injection.
EFI
All systems operate the same way with slight variations to the scheme.
all control fuel flow by varying the duty cycle to the solenoid type injector.
Typical useable range is 10% to 90% duty cycle. Injector flow is not linear but
close between 30% and 70% duty cycle. The cause for non-linear operation is the
injector opening time.
Common inputs baro, engine temp,air temp, rpm, throttle position, manifold
pressure.
optional inputs that are common gear position, O2, exhaust temp, fuel temp,
exhaust back pressure
Injector drive modes
Batch
all injectors fire once per revolution with no regard to crankshaft position or
cylinder phase
Semi sequential
injectors fire in groups similar to a wasted spark ignition better than batch an
a good overall compromise
Sequential
injectors fire according to cylinder phase and it commonly set that you time on
the injector closing rather than the opening as this is the most important
part.
Throttle body
injectors alternate between the barrels of the throttle body in a pattern
determined by the manufacturer.
Tuning modes
all these modes may use many inputs in many combinations as corrections but the
main necessary ones are listed here. Minimum corrections are for air temp water
temp baro and boost..
Speed density
main inputs are rpm and manifold pressure with accel correction from the TPS
sensor
Good for low end street cars and mild turbo applications. Downfalls include poor
response with wild cams as well as poor resolution with them as well. Great for
small transient loads and steady state operation.
Mass air flow
Main inputs rpm and mass airflow correction for accel by TPS sensor. Basically
another street system of little use to real race cars
Alpha N (Throttle position based)
Main inputs RPM and throttle position
Any cam will work just fine, manifold pressure is of no concern at all. This is
a good candidate to convert a NA engine with mechanical injection to
electronics. Resolution is only limited to the size and range or the tables of
the electronics. Baro compensation is typically used with this and is more
critical with this system than speed density.
These systems when well done are seamless for race car use for a street car they
are subject to problems with small load dumps not being taken into consideration
so cruising down the interstate is a little jerky so to speak as the engine goes
slightly in and out of tune at light loads.
These systems are also the only way to correctly run an IR type induction all
the accumulators and tying together the runners to try and get a manifold
pressure reading are just hopeless in the end for anything other than steady
state or slow throttle movement.
Alpha N with boost compensation
Same as above with the baro sensor connected to the boost signal. World class
turbo performance period! Any cam and any boost you can dream of( I have some
cars running a 5 bar map sensor that will read correctly to 58 lbs of boost I
have sensors to go to 10 bar if you are brave enough). Coupled with a sequential
system pretty hard to beat.
O2 sensing
many systems use it but it is generally only useful at low loads and low speeds.
The main problem is it is reactive as opposed to proactive. That is is corrects
for what the mixture was not what it is is now. Coupled with sensor degradation
it is suitable for dyno work but not racing. If you have a system set it up for
good steady state readings and then do a 1000 rpm per second sweep on the dyno..
the numbers will be different by a lot at times. There are 2 reasons for this.
The most important is the length of the loop. The injector is generally many
feet away from the sensor. So changes will have to reach the sensor before it
stops correcting the fuel mixture. The sensor ends up chasing itself a lot in
the end. Good for those that don't know how or won't spend the time to correctly
tune the engine but that is about all when used on the car rather than when on
the dyno. Even worse if if is not a good 5 wire sensor it is subject to +- 10%
error at best from exhaust temp in most cases.
Boost control
self explanatory.. program the boost to whatever the turbo will make according
to rpm and throttle position. This will only lower the boost! Also can be
coupled to gear position and wheel speed or wheel slip :>) This is not traction
control per se it is boost control under a set of conditions deemed dangerous to
the engine running away. When you get into the high boost areas over 32 to 35
lbs this is almost mandatory.
Timing control..
any timing any rpm any load...any curve the engine wants limited only by table
size..
Fuel control
resolution limited by table size good systems are every 250 to 500 rpm and 20 to
32 load sites at each rpm.
This all sounds very complicated but it is not. What it does require is someone
spend the time on the dyno to properly set up the engine the first time. After
that there is very little that needs to be done at the track other than download
the data out of the computer after a run to make sure all the sensors are
working and nothing is damaged. If you are tuning at the track with EFI you did
not do your homework at the dyno or something has changed most often the fuel or
the specific gravity of the fuel ( the reason to monitor the fuel temp of a
known fuel). If it s a different fuel entirely then you have some work to do but
generally no more than changing the overall trim of the system to compensate for
specific gravity..
There are many good books to read on EFI a good primer is
"Bosch Fuel Injection and Fuel Management"
Published by Bentley Books
ISBN 0-8376-0300-5
The BEST way to get started is to purchase a system from a reputable dealer than
has a lot of experience in what you are trying to do and then paying them to set
it up and tuning it the first time and for their time to help you get proficient
in the maintenance and troubleshooting of it. At that point you will be able to
'buff it up' ( fine tune it) as you change engine combinations. This is the same
as any other engine control system you would acquire.
(begining of rant)
Oh I didn't mention carbs because they are just that trouble some in the long
run, the ultimate retro tech, whose first beginnings were a wick and heated
fuel.. They work great for lawnmowers, or anything else that is steady state and
the weather never changes, great too for those who just love to tinker until
their fingers bleed and their hair hurts. Favored by racing organizations that
are comprised of people that can't see the future or love to use the phrase
'when I was young we....' you fill in the rest... I used to have a new Holley
750 in a fishtank in my office but gave it to the neighbors kid to play with in
the sandbox..
(End of rant)
Class dismissed.....
Go win a race my fingers are tired from typing..
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