How to Add Ignition Timing Control to Your Holley Sniper Fuel Injection System
Eric Rosendahl is an early EFI adopter and converted his 468ci big-block El Camino to a Holley Sniper throttle body fuel injection system right after it was introduced. It’s been on the car now for over two years and he couldn’t be happier with how well the big Rat motor runs. He matched it with a Sniper fuel tank and high-pressure, internal electric fuel pump and cold start is now new-car-like and his highway cruise rpm with the 4L60E overdrive automatic often achieved 14-15 mpg. For a healthy 525 hp Rat, that borders on impressive.
During the original Sniper installation, Rosendahl followed Holley’s recommendation and fine-tuned the fuel side first before converting to electronic ignition control. With thousands of successful miles on the TBI conversion, the time was right to upgrade the ignition side. The current ignition consisted of a simple HEI distributor but the big Rat balked at adding any vacuum advance since it would detonate if he tried adding anything more than 12 degrees initial timing and 22 degrees of mechanical advance. The promise was that digital control over the ignition could improve drivability by adding non-linear finesse to the ignition curve.
There are three ways to go about combining digital spark control with the Sniper system. Option one is to update to a Holley Dual Sync distributor that incorporates both a crank and cam sensor in the distributor along with a circuit board. The second option is to use a Holley HyperSpark distributor which is the path we chose. The third avenue is to use a typical MSD distributor, lock out the mechanical and vacuum advance mechanisms and then go through a distributor phasing procedure using an adjustable rotor from MSD.
Our main reason for choosing the HyperSpark distributor was because Holley has created a very simple and ingenious way to quickly and easily set the distributor in the engine and phase the distributor. This is achieved with the use of a clear plastic cap that fits over the rotor which makes it incredibly easy to phase the rotor. We’ll show you how it works.
The first step was to remove the spark plugs to allow turning the engine over by hand with the crank bolt. We decided the engine was probably in need of a new set of plugs anyway along with new MSD plug wires. We then rotated the engine to bring the crankshaft to top dead center (TDC) on the Number One spark plug. This is done by placing a finger over the spark plug hole as the engine is slowly rotated. With cylinder pressure building and the TDC mark on the balancer approaching the timing tab, carefully line up the mark on the balancer to zero (0º) timing, which is TDC. If you overshoot, don’t reverse engine rotation but rather turn it over two full revolutions and set 0 degrees by carefully moving the crank with a socket and ratchet instead of trying to bump the engine with the starter motor. We had to raise the front of Eric’s car with a jack to allow sufficient room to turn the engine over with a breaker bar on the crank bolt from underneath because the accessory drive is very close to the twin electric fans, reducing working room.
Next we removed the HEI cap and plug wires and distributor. On a small- or big-block Chevy, the normal engine rotation turns the distributor rotor clockwise, so note that as the distributor is removed, it will rotate in the opposite direction (counterclockwise) as it rides up the helical cam gear teeth. Now we could install the new HyperSpark distributor. Make sure to place the distributor gasket over the body and then carefully insert the distributor into the hole and watch how the rotor twists into place. We want the rotor to point in the same direction as it did when the old distributor was removed.
In most cases, including ours, the distributor body will not drop all the way into the distributor hole. This is because the oil pump drive tang has not engaged the male tang inside the distributor gear. You can turn the oil pump drive shaft with a long flat screwdriver to help align the tang, but that trick doesn’t always work. We prefer to drop the distributor in then turn the engine in the normal rotation until the distributor drops into place. Sometimes this requires a slight downward pressure with your hand on the distributor body. Once the distributor is positioned properly, turn the engine until compression is felt on Number One and again place the harmonic balancer mark at 0 degrees.
Now place the clear plastic cap over the rotor and rotate the distributor body until the two small pins on the distributor fit inside the small insert in the clear plastic cap and the rotor is also nestled into the clear plastic cap. This establishes the proper orientation for rotor phasing for the HyperSpark distributor. Tighten the distributor hold-down bolt to secure the distributor.
We marked our HyperSpark distributor body with a Sharpie to indicate where the Number One spark plug wire should be positioned on the cap. The distributor cap only fits on the distributor body one way and this mark will determine where the Number One plug wire will be located. You will also need to know the firing order to accurately place the spark plug wires. All Chevy V8 engines with distributors use a 1-8-4-3-6-5-7-2 firing order.
With the HyperSpark distributor in place, we also mounted an MSD coil bracket and canister style coil that is compatible with the inductive ignition. The Sniper throttle body can also be oriented to use a capacitive discharge (CD) style of ignition that would include a capacitive discharge amplifier box and matching coil.
We chose to run the more traditional inductive ignition and a canister style ignition coil. The main reason for this is simplicity and it is more affordable than using a CD system. This inductive system does require a small amount of specific wiring to connect the four wires leading from the coil driver module. As shown in the accompanying schematic, the wiring is the same for both the Dual Sync and HyperSpark distributors as both use Hall Effect triggers.
There are four wires that must be connected from the inductive coil driver module: pink, black, grey, and white. The pink wire is switched 12v+ power, black is a ground, the grey connects to the negative side of the coil, and the white wire is the rpm sensing wire that is connected to the ECU. That’s it. We prefer to use non-insulated butt and terminal connectors and then insulate these with a heat shrink tubing to make a professional connection.
With all the wiring in place, we next accessed the Holley website to download the latest version of the Sniper EFI software to ensure that both the ignition and fuel sides of the Sniper were all using the same version. Once this was accomplished, we enabled power to the Sniper and called up the ignition Wizard on the handheld and inputted the HyperSpark distributor under ignition type. This tells the Sniper unit which distributor will be used.”
How to Upgrade Your Sniper EFI Software
With this configured, the next step in the instructions had us disable the fuel pump relay and crank the engine with a timing light connected to ensure the initial timing was at 15 degrees BTDC. After timing was verified the fuel pump relay was reconnected and the engine immediately started. We shut the engine down and using the Sniper hand held, accessed advanced timing and locked the ignition at 15 degrees. Locking the timing out is used to verify that the timing the ECU is commanding is actually what’s happening at the engine. This lockout feature is set to 15 degrees. We started the engine and the timing light indicated only 12 degrees, which meant our distributor was off by only 3 degrees. We simply loosened the distributor hold-down bolt and moved the distributor body until the timing mark on the balancer matched 15 degrees BTDC.
Once the ignition is shut off, the lockout feature is disabled. So if you want to check it again, you must go back through the process of locking it out again in the handheld.
As part of the normal Sniper ignition controls, there are only three timing inputs: idle, cruise, and WOT. Rosendahl chose to download the software from Holley to created a personalized spark map on his laptop in a 2D format with timing based on rpm and load expressed in kPa. The top of the vertical scale at 95 kPa is WOT while the bottom of the map at 1 is very high manifold vacuum as seen in deceleration.”
Our initial map was copied from the basic Sniper ignition curve as shown in the accompanying photo. We spent a couple of minutes attempting to optimize the timing curve for this particular engine and what we had observed it liked during road testing. If you want to know more about how to create your own custom curve, Holley has a great instructional video on the details of this process.
We then took the El Camino out for a test drive and noticed the big Rat detonated slightly at part throttle acceleration up to freeway speed so we modified that spot by reducing the timing by 3 to 4 degrees. We also increased the light cruise timing from our initial 36 to 40 degrees which is conservative (it may increase to around 45 degrees once we have more time to evaluate the change) but even on this first test drive the system performed extremely well.
In fact, the next day Rosendahl drove the El Camino on a 124 mile highway jaunt and the big-block consumed a mere 6.8 gallons which computed to an amazing 18.2 mpg. This might be a bit optimistic for a 468ci big-block with a 4L60E lockup overdrive, but nevertheless points out how well the system performed right out of the gate. The previous HEI was not able to use the vacuum advance due to detonation issues and was generally able to deliver around 15 mpg on the highway.
Our efforts to digitize the El Camino’s advance curve were tremendously successful. The engine feels stronger with improvements in both throttle response and fuel economy. Plus we can make WOT timing changes with one degree accuracy with a simple keystroke. It’s especially fun when a simple afternoon upgrade returns such positive rewards.
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