Two Step Rev Limiting a Blown Alcohol Engine

For years Two Step Rev Limiting has been done on non-blown applications like Pro Stock on down to Stockers. Now blown applications are starting to use this technique for more consistent starting line launches. The following will help with the necessary parts and a wiring diagram.

Parts needed:
1 – 8147, 44 amp points box with built in rev limiter.
1 – 8737 Two Step Module Selector.
1 – Control switch pneumatic or electric.Optional,
1 indicator light.

The Two Step will plug into the RPM limiter socket of the 8147 Points Box.The Red wire will connect to the clutch switch.The Black wire connects to Ground.
Module 1 = Low RPM Limit.
Module 2 = High RPM Limit.
The most important part of the installation is the mounting of the switch. It should be located on the clutch pedal for the most consistent performance. The clutch switch will provide power to the Two Step on the Starting line. When the clutch is engaged it will switch from “Module 2” to “Module 1”, “Starting Line Limit”. When the clutch is not engaged the Two Step will be in Module 2, “High RPM Limit”

An optional indicator “light” will aid in adjusting the clutch switch switching “off” to the actual clutch engagement. The light will connect to Red wire of the Two Step, turning on when the clutch pedal is depressed. The clutch switch should be able to be adjusted according to clutch air gap. As the clutch is released slowly the indicator light should switch “Off” releasing the low limiter as the clutch is being engaged. This should provide a smooth transition from staging to launching, preventing a bog or excess wheel speed.

Reading RacePak Timing Charts

You will need Acrobat Reader
to view diagram, download it here.

This chart is intended to help you interpret the data from a RacePak data recorder.
If a problem arises, the information presented here should help you find the origin of the problem.
For starters, the data collected from: TDC indicator, Delay Box 1, Delay Box 2, Engine 1 and Engine 2 is real (“raw”) data and the traces should lay on top of each other if correct.

Traces showing timing stability and / or changes use calculated values. They indicate when a timing change occurred and the duration of the timing event.
By performing calculations on data taken from the Delay Box Tach Outputs, the TDC Indicator, and the Optical Pickups on the coil primary leads, ignition timing changes can be monitored.

For example:

Delay Box Tach Output vs. TDC = Delay Box Timing
Engine RPM (from crank trigger pickups) vs. TDC = Optic Timing

In some cases, when the data is downloaded into the P.C. and only the timing graphs appear incorrect, try downloading the information again. Sometimes the data is merely corrupted during a transfer and any traces using calculated values may appear abnormal.

If at any time you should lose the TDC indicator, all the timing graphs will be corrupted or lost.

Servicing Deutsch Connectors:

How to check connections and crimp qualities:

To check connections pull on wires to make sure that pins are not loose in connector shell. If the wire does pull out, inspect the crimp to see if the wire is crimped on properly. Crimp can be recrimped using 3510 with 3505 crimp tool simply push pin connector in until it "Clicks" back into place.

When making pin repairs make sure that the heavy Red and Black wires are crimped and soldered.
Pin location code:

44 amp mags (Deutsch connector)

#1 = Violet 18 AWG
#2 = Green 18 AWG
#3 = Black 12 AWG
#4 = Red 12 AWG

12 amp + 20 amp (Deutsch connectors)

1# = Violet 18 AWG
2# = Green 18 AWG
3# = Black 18 AWG
4# = Yellow 18 AWG

Magnetic Pickup Connectors

Generator W/ Retard
1# Black/ Violet = Green 18 AWG Green = None 18 AWG
2# Black/ Orange Violet 18 AWG Violet = Yellow 18 AWG
Replacement connector PN 8824

Torque Spec for Cross Drive Nut

Torque Spec for cross drive nut = 20 ft/lb

Strange Looking Head Gaskets and Bearings

You will need Acrobat Reader
to view diagram, download it here.

If you have noticed strange line-like markings or evidence of electrical arcing on you head gaskets, pistons or bearings, chances are you may have a magneto grounding problem. Visualizing the secondary current flow, it would start at the generator, pass through the points box to the coil, through the cap, rotor, wires and end up at the spark plugs in the heads. It should then complete the path back to coil (-), which is ground. However, if the path between the cylinder heads and coil (-) is not optimized, the current will generally find or make it's own path to complete the circuit. Often it is assumed that motor mounts and head studs will provide adequate ground when they really don't. To address this issue, we now suggest that both heads be grounded to a single point via a braided ground. This point should be the same as that shared by both coil (-) leads.

Note: If a Timing Retard PN 8168 is used, make sure that the points box case or cases are grounded to the retard box case. If this is not done, you may experience poor engine performance and "noisy" data traces on the RacePak display.

Do Not Do This!!!

Do not use 12 amp "Kill Switch" on 44 amp mag systems!
Do not use one kill switch for two mags.
The 12 amp kill switch is jut not adequate for a 44 amp Pro Mag -the contact distance is not sufficient and arcing may occur across the terminals inside the switch.
Please use PN 8101 air kill switch for a 44 amp Pro Mag. It has 7/8" separating the contact pins for safe, reliable operation.

Rev Limiters

People often ask "What happens if you pull the RPM module out?" On units with Rev Limiters, the limiter function will be effectively bypassed if a chip is not installed (i.e. no rev limiter).

On 44 Amp Pro Mags you can order a points box with or with out a rev limiter.
PN 8147 with a rev limiter
PN 8145 without a rev limiter.
The 8147 limiter box is slightly larger to accommodate the limiter circuitry. Insert photo of RPM module and socket with and without RPM module.

When using the retard box, PN 8168, the timing will revert to the total mechanical timing if the retard module is removed. The same applies to any stage of the Six Shooter, PN 8158 although we do recommend inserting 0° modules to avoid noise problems.

Broken Woodruff Keys

After any engine explosion, check the bottom drive woodruff key. In some cases when the engine stops suddenly the woodruff key can shear. The size of the key is engineered shear in such an event as not to cause other damage else where in the generator.

8101 Pro Mag Kill Switch

We now carry them and have them in stock on the trailer.

Spark Plugs

There are times when an engine may drop a cylinder or cylinders for no apparent reason. After researching this problem we found one answer, it could be the spark plug. We discovered that porosity or inclusions in the porcelain may allow the spark to travel through the porcelain directly to the metal shell of the spark plug. Looking at the spark plug, it would appear that the plug never fired. One can inspect the spark plug by cutting it apart on a lathe. Machining the crimp off will allow the porcelain insulator to be removed and inspected. Once removed, pin holes or burn marks can be seen with the naked eye. If viewed with a microscope, the evidence is quite clear.

8830 Capacitor

If a battery is being used, a capacitor should be installed across the battery leads. The capacitor will store enough energy to run most timing accessories should vibration cause an open or short in the battery.