DIY mapping experience

[Oliver Sedlacek]

I thought I'd share my experiences trying to map the ignition myself. When I initially installed the Megajolt I just loaded up a map that matched a standard distributor. With a bit of tweeking it ran better than a distributor, and gave better gas mileage. Just fiddling with the map didn't really make much difference, so I left it like that for a while.

Recently I thought I'd like to do better, and I eventually came up with this methodology for tuning the low RPM response, which really affects street driving. I decidied to focus on a smell RPM band, in this case 1000 RPM to 2000 RPM, which is covered by three map RPM points. I measured how much throttle the engine would take whilst accelerating from 1000 RPM to 2000 RPM in top gear. This meant holding the engine at the limit of audible knock and using the TPS to measure the throttle opening. I then retarded the ignition map at these points and repeated the process.

This is a somewhat timeconsuming process, but I'm really pleased with the results so far. Running the engine into knock is not ideal (but it's only brief) and I don't know how to do higher RPM bands, but the concept of only trying to tune a small region is paying off for me.

[brentp]

Sounds like the inexpensive way of doing the same as tuning on an load bearing dyno, like the Mustang. Tune for maximum torque in each RPM band, under varying conditions.

The thing to consider is to have enough margin for varying ambient conditions, or when the coolant / air inlet temperatures start rising - in which case you'd want to pull back ignition timing to save the engine.

I'm considering doing this on our race car as a type of 'fail-safe' in cases of slight overheat situations.