Fuel & Ignition Systems

Fuel System:  Edelbrock #3500 Pro-Flo fuel injection system controlled by Holley's Commander 950 Management System. The combination includes a Victor Jr. style intake, 1000 CFM 4V progressive style throttle body, 30# Ford SVO injectors (set at 57 psi which equals a 36# injectors), BBK #1714 adjustable fuel pressure regulator for TPI systems, Edelbrock in-line fuel pump, K&N 14"x3" air cleaner, homemade "cold-air" box.

Ignition:  Procomp Electronics distributor #10001 (late model small cap HEI), MSD #8207 Blaster Coil, MSD 6A #6200 ignition box, MSD 8.5 mm Super Conductor plug wires, NGK #3686 - FR45 V-power spark plugs (.050 gap), Optima Red battery, Summit #811001 One-Wire 100 amp black alternator, Summit #2000 billet aluminum alternator bracket.

EFI - Front View   EFI - Driver's Side View   EFI - Passenger's Side View   EFI - Throttle Body  



The Fuel Injection Systems:


Originally I had installed a stand-alone Edelbrock #3500 Pro-Flo fuel injection system, using a Mallory #8548201 cast 356 T-6 aluminum HEI distributor (converted to Edelbrock's Hall Effect sensor). The Edelbrock package is a very cost effective Speed-Density system, utilizing a hand held calibration module that eliminates the need for a laptop. However, where that may be an advantage to some, it later became a disadvantage in my mind. The Pro-Flo's tuning capabilities are very limited (i.e. no datalogging or wide band O2 input and control).

Edelbrock 3500 System

I would like to add that the system did work fairly well, but was extremely sensitive to high air temperatures. And, Edelbrock does have an EFI technical support team that was awesome to work with.

Knowing what I know now, if I were to buy another complete fuel injection system, I would buy either Holley's single plane Commander Multi-Point system (below left) or their Stealth Ram Multi-point system (below right). The cost of either Holley system indicated below is more than the Edelbrock Pro-Flo system, but the few hundred dollar premium would be well worth it when considering the flexibility (datalogging, WBO2, and expandability) of the software and the choice of injector sizes.

MPFI with top mounted TB        Stealth Ram - Assembled  Stealth Ram - Components


After researching other aftermarket engine control systems, I decided to upgrade to Holley's Commander 950 Management System kit, which is also a Speed-Density system. There were four things that convinced me the C950 system was best suited for my application.


1.  Cost:  The 950-101 system which is for GM TPI engines, was $906.36* from Summit Racing (HLY-950-

101). This includes the ECU, software, base maps, harness, MAP sensor, air temperature sensor, 3-wire heated oxygen sensor, and main relay. Because it is designed for TPI systems, it also includes the adapter harness (P/N 950-138) for small cap HEI distributors. *Purchased in June 2005

2.  Features (Power & Versatility):  From page 144 of the www.Holley.com Fuel Injection Catalog:




The Holley Commander 950 ECU provides the customer with a high level of tuning flexibility to control engines from mild to wild. From stock, naturally aspirated engines, to high horsepower supercharged engines, the Commander 950 gives you the power to precisely tune all functions of an engine.

The Commander 950 allows for real-time tuning of all parameters. The Windows-based software is simple to use for the beginner and has all the features necessary for experienced tuners.

All Commander 950 Systems comes standard with the Pro Software. Pro Software comes with many features that help allow the precise tuning of any street or race engine.

C950 Wiring Harness & Computer




  • Compatible with 4, 6 and 8 cylinder even fire engines
  • Operates as speed density or alpha-N
  • Can be programmed to run alpha-N at idle only
  • 16 x 16 fuel and timing maps
  • Uses 1, 2 or 3 Bar MAP sensors
  • Maximum RPM of 12,750
  • Controls GM and Chrysler stepper IAC valves
  • Compatible with GM knock sensor
  • Controls 8 high or 4 low impedance injectors - will control 8 low impedance injectors w/ P/N 534-122
  • Operates in closed and open loop
  • Controls narrow band and any wide band O2 sensor with 0-5 volt output - 8 x 8 target air/fuel ratio chart
  • Full tuning for:
    - startup and warm-up fuel enrichment
    - acceleration fuel enrichment based on
  • MAP and TPS sensors
    - timing vs coolant temperature
    - deceleration fuel cut-off
    - fueling strategy
  • Timing control feature can be acheived through the use of:
    - small cap computer controlled GM HEI (stock or aftermarket)
    - large cap computer controlled GM HEI
    - Ford TFI distributor
    - magnetic crank trigger and hall effect crank trigger
  • Integrated rev limiter
  • PC and internal datalogger (logs to ECU) standard. Fully programmable operation
  • Programmable inputs and outputs (timing retards, RPM activated switches, fan controls, AC input to raise idle, etc.)
  • ECU size is 5.5" x 4.75" x 2.0"


3.  User Friendly:  From page 145 of the www.Holley.com Fuel Injection Catalog:



The Holley software included is Windows-based. It is designed for beginning users or expert tuners. The software is compatible with Windows 3.1, 95, 98, 2000, ME and XP operating systems. A computer with a 9-pin serial port is required. The software allows real-time tuning whether on the dyno or tuning on the street.

All sensor data is viewable from both fuel and ignition timing maps which makes tuning easier. The fuel and ignition timing maps can be viewed in graphical form, which helps to better visualize the data. Hot keys allow for quick navigation between screens. Other features such as warning the user when a fuel map number is entered that drives the injectors static makes tuning safer.

A comprehensive, step-by-step tuning manual is included, along with many base maps to get you started and assure success.

A professional level data-logger is included for evaluating on-track performance.

A copy of the comprehensive 100 page Owner's Manual can be downloaded at www.holley.com


This manual is without a doubt the best tool I have ever seen when it comes to understanding EFI. It not only is great for setting up and tuning the C950 system, it is also very good for understanding general EFI terms and components that are applicable to many other systems, including GM's stock systems. Note - If your laptop does not have a serial port, you can still use the included serial cable, but you will have to buy a serial to USB adapter, such as this one from Innovate Motorsports. Below are some examples of just how user friendly the C950 software is:

C950 - Main Menu Screenshot   Screenshot - Engine Parameters


Screenshot - Acceleration Enrichment   Screenshot - Fuel Map   Screenshot - Fuel Graph   Screenshot - Datalogger


4. Technical Support:

Holley has a toll-free phone number to there technical support staff, including EFI specialists. This service was invaluable when researching and deciding on a new engine management control system.

There are many technical forums on the internet. But the EFI forum at www.chevytalk.org is moderated by Doug Flynn with Holley. There are also a number of members who use the C950 system in their cars.

Check out "64duece" and "zwede".


Commentary and Pictures on the Swap to the Holley C950 ECU & Harness:

Since the Edelbrock system utilizies many common sensors as a GM and Holley system, I decided to purchase the most cost effective C950 system, which part no. 950-101, for GM TPI systems. In order to make this swap, I had to convert my IAC from a Ford Style throttle by-pass valve to a stepper style. I bought the adapter block, stepper style IAC (Chrysler type used on Holley systems), and gasket direct from Holley. In lieu of cutting the original Edelbrock harness, I bought new plugs for the TPS and IAC connections. These were spliced into the new Holley harness using quick-connect type fittings. I also purchased a new late model small cap HEI distributor to make the swap a plug-in on the ignition side. I incorporated my MSD 6A box using the wiring diagram included in Holley's C950 Owner's Manual.

Remove the old Edelbrock ECU and harness. Look at the difference between the harnesses. The Holley harness is the lower one in the picture below.

Old Pro-Flo ECM Harness Penetration   Old Pro-Flo ECM in Glovebox   Firewall Hole for Old Edelbrock Harness   Compare Wiring Harnesses  


After installing the new Holley harness, I can tell you that it is much easier to fit in the car, at least in my Camaro. I had to fabricate some sheet metal pieces to form a 2" diameter opening for the Holley harness. This was done to clean-up the hole and use the big rubber grommet provided by Holley. If installing this from scratch, I would have used a 2" dia. hole saw. But whatever you use to cut the opening, be very careful of items obstructed from view behind the firewall. You can see how close a vacuum canister for the HVAC controls is located behind the hole. The little curled up piece of hard tubing is my vacuum source for the HVAC vent controls. The new Holley ECU fits nicely inside the glove box area. But since I mounted it to plastic, I was sure to run a ground to the engine. You can see the loop in the picture below:


Compare ECMs   Holley ECM in the Glovebox   Hole in Firewall for New Holley Harness   New Holley Harness Installed  


I had to remove the Ford style by-pass valve for a stepper style IAC, such as the one used on Holley MPFI systems. Holley uses a Chrysler stepper style IAC with a bolt on connection and a flat four pin plug. I purchased an aluminum adapter plate, gasket and IAC directly from Holley. I spliced in a plug purchased from Carquest (P/N S-551 -about $20) which works perfectly. When splicing the IAC wires, the connections are as follows: Purple/White (IAC "B" Lo) - C, Purple/Black (IAC "B" Hi) - B, Purple/Yellow (IAC "A" Hi) - D, Purple/Blue (IAC "A" Lo) - A.

Splicing the TPS was just as straightforward. I used a plug also purchased from Carquest (P/N S-574 - about $15). For the Edelbrock TPS, the connections are as follows: Black/White (Analog GND) - A, Green (TPS signal) - C, Orange (+5 Volt reference) - B.

Old Edelbrock Ford Style IAC   Old Edelbrock Ford Style IAC   Compare Old & New IACs


New IAC & Adapter Installed   Close Clearance on Adapter to Bracket   Picture of TPS


Installing a new small cap HEI distributor and remote mount coil. I purchased a new billet distributor from Procomp Electronics. This is a MSD knock-off at one-third the cost. It is manufactured in Australia. I purchased an MSD #8207 E-coil and mounted it to the firewall. Since the coil has rubber isolator mounts, I had to fabricate a sheet metal bracket that could be attached to the fire wall. The rubber mounts use nuts and there is not clear access behind the fire wall. The spacer plate is attached with four sheet metal screws, spaced with 3/8 nuts. Before installing the new distributor, I set it to 10* BTDC on the No. 1 firing order. I test fit the new distributor without the gasket to make sure it would not be in a bind. I installed the new gasket and distributor and installed a nice billet clamp, also from Procomp Electronics.


Set the Damper to 10* BTDC   New Procomp Small Cap Distributor   Distributor Installed - Pass Side View   Distributor Installed - Driver Side View


Billet Hold Down Tab   Hold Down Tab Installed   Fabricating a Sheet Metal Bracket for the Coil   Coil, Distributor and Wires Installed


Since I felt my engine needed bigger injectors than what came stock with the Pro-Flo system, I decided to upgrade to some cost effective, yet durable injectors from Ford. Their SVO 30# injectors are only $230 from Summit Racing. Since they are rated at 40 psi, by increasing the pressure to 57 psi, I have in change the injector rating to 36#. This will work nicely with the base map I installed (383SBC36), and give me comfortable level of HP potential for both the injectors and my engine combination. In the picture below, you can see the original 28# Pro-Flo injector (Pintle style rated at 51 psi) and the Ford units. The blue is a 24# SVO unit and the red is a 30# SVO unit. Both the Ford are pintle style injectors as well.

Note: when installing injectors, always remember to install them in the rail FIRST. I knew better, yet failed to do this. Luckily I only damaged two O-rings in the process. Take note of the incorrect installation in the bottom left picture, the large gap between the rail and the plug area. The correct installation is shown in the first two picture below. I also installed a separate relay for the fuel pump. Holley states that fuel pumps that draw 10 or less amps can be powered directly from the harness wire. I opted to install a separate 15 amp fuse with a 30 amp relay, and used the fuel pump wire from the Holley harness only to activate the relay.

New Injectors Installed - Pass Side View   New Injectors Installed - Driver's Side View   Compare Various Injectors


View of New Injectors & Distributor   Torn O-ring   Fuel Pump Relay & MSD Box