Spark cut instead of fuel cut?

[skyline_stu]

Yes, your totally right. It becomes a big air pump - much like a decel fuel cut off.

Where the main problem is that many cheaper aftermarket systems have very poor strategies and a small recovery window, like simply cutting off half the injectors. When the injectors come on again, the fuel delivery may be unstable for a few engine cycles due to boost pressure fluctuations. Then you hit on the limiter again repeating the cycle. Typically, the rev limit is active at max rpm and max load, so the injectors provide stuttering fuel delivery, poor afr's and broken parts, This is why there are often several cut and recover points (hysteresis or delay). These unfortunatly cause the harshness of many limiters.

Well thought out systems progressivly cut one cylinder, then more as needed to control RPM, while allowing all cylinders to do an equal amount of work in any given time period.. Motec, for example call it the randomizer - there are 255 types of different cylinder cut sequencing, some modes work better than others to reduce excessive crankshaft torsional vibrations.. You need to understand the physics of what's going on inside the engines at cut point.. I firmly believe most RB26 oil pump failures are due to excessive/prolonged rev limiter use with incorrect vibration/torsional damping. You read it here first !!

And hence, because of these bad experiences that many people have had, the urban 'automotive' legend of spark vs fuel being better came about. Combined that with a lack of understanding and human natures' love of passing bad or misleading information, these rumors just won't go away.

We all know of those 'friends's brother's cousins mate who said spark cut is the only way to go', even though he works in a take away shop!! Magazine journalists get too much stuff wrong..

I'll leave it at that..