Holley COMMANDER 950 - Manual (Page 67)

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Hot Start Delay – The amount of time the engine will wait before entering closed loop operation when the engine is restarted
while still hot. This should be about 30 seconds.
RPM to Enter Closed Loop – Any rpm above this point will activate closed loop.
RPM to Return to Open Loop – If the rpm falls below this point, open loop operation will occur. This setting should be about
100 rpm below the rpm to enter closed loop. This is so that the ECU doesn’t not “hunt “ between open and closed loop
operation.
Minimum Engine Temp – The minimum temperature of the engine is set before the ECU enters closed loop operation. This
value is typically set between 100 to 160° because below that the engine will run rough if trimmed to a 14.7:1 air/fuel ratio.
Maximum TPS for Closed Loop Operation – An engine needs to run at an air/fuel ratio richer than stoichiometric at WOT
conditions; be sure the closed loop control is turned off and doesn’t try to lean out the fuel mixture. Depending on the throttle
body design, this value is usually about 2/3 of wide-open throttle.
Appendix 2 APPLICATION SPECIFIC TUNING
Specific Information For Race Applications
Many drag racing classes are allowed to run EFI. More popular classes are Stock Eliminator, “Super” classes (9.90, 8.90),
bracket classes, NMCA and NSCA Super Street, Pro Street, and EFI eliminators, Mustang Shootout Classes, Import Racing,
and many others. The Commander 950 is suitable for many of these.
Stock Eliminator allows the use of EFI. The most common engines that run it are TPI (L98), LT1/LT4, LS1 engines, and 5.0L
Ford. The Commander is very suitable and has been successful with all of these engines. TPI engines can use PN 950-101
for an ECU and harness kit. LT1/LT4 use PN 950-105. These engines require the use of a crank trigger. LS1 engines use PN
950-102 and require the use of DIS (distributorless ignition system) PN 800-501 and a crank trigger. 5.0L Ford engines use
PN 950-106.
A special note on LT1 engines. A common problem is for the rotor tip on the opti-spark to come loose. It is advisable to
epoxy the end of the rotor tip.
One of the main tuning decisions to be made with these engines is whether to run Speed Density or Alpha-N. The following
briefly reviews the two methods.
Speed Density: Uses a MAP (Manifold Absolute Pressure) Sensor to determine engine load. It takes the load and RPM to
determine a fuel pulse width value from the fuel map. The sensor reads from 29 In/Hg vacuum (0 KPa) to atmospheric
pressure 0 In/Hg vacuum (100 KPa). Simply, this means it reads from high vacuum to wide-open throttle conditions. This
method is very good at sensing engine load changes. The limits of speed density are engines that generate very low vacuum
at idle. Engines that have less than 9 In/Hg (70 KPa) of vacuum at idle are possible candidates for Alpha-N. Getting speed
density systems to idle properly is a function more of proper tuning rather than limitations when large camshafts are used.
Engines that have a 2 or 3 Bar MAP sensor for boosted applications MUST run Speed Density.
Alpha-N: Uses the TPS (Throttle Position Sensor) to determine engine load. It looks at the TPS and RPM to determine a fuel
pulse width value from the fuel map. Alpha-N is not able to truly sense engine load. For example, the fuel that is injected at
idle with the throttle fully closed is the same fuel the engine will receive when the car is put into gear with the throttle fully
closed because the TPS didn’t move and the ECU can’t sense the change in load. This is not as much of a problem with all-
out race engines that are rich at idle and idle at higher RPMs. Alpha-N should only be used when a satisfactory idle can’t be
obtained with a speed density system.
Both systems have fuel map designs that have characteristics specific to each type.
Most Super Comp type engines are typically run Alpha-N. Many Stock Eliminator engines are run speed density.
Oxygen Sensor in Race Applications: The oxygen sensor used in the Commander 950 has very limited use in race
applications due to several reasons. If a vehicle has open headers and/or short collector extensions, mounting the sensor in
the collector allows back pulses of air to affect proper readings along with possible problems from low exhaust gas
temperature levels. The sensor output, when operating properly, only gives the individual an idea if the engine is richer or
leaner than stoichiometric (14.7:1). This is not of significant use in a finely tuned race application. Leaded race fuels also
degrade the sensor over time and any readings it does emit have to be suspect over time. However, the output from it can be
data-logged to give an idea if the fuel map might need to be changed as weather conditions change. For example, if it is
reading .8 volts and drops to .75 volts when the air changes, it is a sign that the fuel map may need to be richened.