Miller's Mule Blog

In this post I’ll show you how to generate an ignition map MegaJolt in a RPM only mode. This will most closely resemble the behavior of a weight and spring distributor.

If you were to spin a distributor through an engine’s operating RPM and then record the degrees of advance it generates, you would get a graph similar to the one below.

2d Ignition Map

Here we see our engine has an operating range from about 500 to 7500rpm. Max advance of 32 degrees is achieved at about 3800rpm, and static advance is 12 degrees at about 800rpm. This is the exact terminology used to describe ignition curves of mechanical distributors. Now we just need to translate this terminology into a map or spreadsheet that MegaJolt can understand. This looks like below:

RPM vs Advance Table

RPM bins are represented across the top while the colorful numbers represent degrees of advance. Lets say your engine is running at 2000rpm. MegaJolt will look at the table above, and say “oh! we need 29 degrees of advance!”

However, if you open the MegaJolt Configurator software, you won’t see a table like above.  You’ll see one like what I have pictured below.

Table View

MegaJolt only understands maps with 100 bins. It likes to also use load sensing (MAP or TPS) to look up advance values. We can trick MegaJolt into not caring by copying our simple 10 bin map down each row.

MegaJolt will turn this into a 3d map like below. If you look at the profile of the curve/surface though, you’ll find it is exactly like the curve at the top of this post!

Megajolt Configurator View

You could copy all of the data above manually. Luckily though, MegaJolt works off of a settings or configuration file.  You can download a copy of the above generic RPM only configuration here and then load it into your own MegaJolt! Easy peasy!

For a more advanced map, try Mapping MegaJolt: MAP and RPM, or Mapping: TPS and RPM.

MegaJolt allows many modes of operation. I’ve listed these below, in order of basic to complex. In general, the more resolution (bins) you have, the better. More bins will allow you to tune ignition timing more closely to the ideal ignition timing. Ideal timing will reduce emissions, improve fuel economy, and increase an engine’s power output.

• RPM Only
  This mode is often overlooked, it only uses the RPM input to calculate advance. This mode is most like a standard mechanical distributor with weights and springs. This will produce a 2-dimensional map (RPM and Ignition Advance). You only have 10 bins to work with though. See: Mapping MegaJolt: RPM only
• MAP and RPM
  This mode calculates advance given Manifold Air Pressure (MAP)  and RPM as inputs. This will produce a 3-dimensional map. In this mode there are 100 bins (10×10) to work with. MAP and RPM is ideal for most applications such as single carburetors, mechanical fuel injection, and early electronic injection (Bosch L-Jet etc.) It is the only way to go for boosted (turbo or supercharged) applications.
• TPS and RPM
  This mode calculates advance given Throttle Position Sensor (TPS) reading  and RPM as inputs. This will produce a 3-dimensional map. In this mode there are 100 bins (10×10) to work with. TPS and RPM mode ideal for situations where a steady vacuum signal is not available such as with dual carbs, or individual throttle bodies (ITB’s).
• Adjustments to Advance (Advance Correction)
  In addition to the modes above, you can add another layer of complexity to adjust ignition advance. This can be done via just about any external sensor sending a voltage signal to the MegaJolt. The most popular, and usually most effective, is through the use of an Intake Air Temperature (IAT) signal. This will act somewhat as a multiplier, giving you extra depth to each bin, producing a 4-dimensional map with 110 bins (10×10+10).