Join Date: Dec 2008
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A little history:
Calum brought the issue of the 8012.5 RPM limit to my attention last year saying that if I could figure out how to fix it, a number of people in the community could benefit. Once resolved, we naturally started asking ourselves; Why would the Nissan engineers impose this RPM limit? After many hours (actually days) scouring the code for possible ramifications, and also running an ECU on the bench to very high RPM levels, no apparent problems were found. This does not mean that none exist! (See Caveats below)
What the mod does:
Basically it removes the 8012.5 RPM limit, such that the RPM value used to compare rev limits, perform fuel and timing map lookups, calculate TP, etc., is allowed to increase above 8012.5 RPM when the engine actually revs beyond that.
What the mod means:
The simplest and easiest to implement benefit of the mod is to be able to set rev limits above 8012.5 RPM that actually work. Another benefit is the ability to tune fuel and ignition maps above 8012.5 RPM. This a little more involved, in that it requires the user to 1) rescale the fuel and timing RPM scale tables to expand the RPM range and 2) to re-tune the fuel and ignition maps accordingly. If only the scales are expanded, the fuel and timing maps will be offset such that the map value at what was 8000 rpm is now reached at something less. It also obviously means that the RPM must reach the upper end of the rescaled values in order to use the map values in the far right column. Therefore, after rescaling the RPM scales, the values in the maps must be changed accordingly, or you will probably run lean and retarded throughout the RPM range.
Another aspect that may need to be considered is TP (theoretical pulse). Most of you already know that TP ~ K x Q/N where K is the injector K constant, Q is the air mass flow rate from the MAF VQ table, and N is RPM. Without the RPM mod, N stops at 8012.5, which means that TP continues to climb relatively more quickly as Q increases with RPM (if it actually does with your setup). This tends to automatically richen the AFR. With the RPM mod, N continues to climb with Q such that the TP calculation stays balanced, as long as the MAF sensor doesn't max out. What this means is that the TP scales for the fuel and timing maps, along with the TP Max table, may also need some adjustment.
A couple of obvious ones, that don't really have anything to do with this mod are 1) your MAF sensor does not peak below your desired max RPM, and 2) your injector duty cycle at the higher RPM stays within reason. Caveats that do pertain to this mod are potential, unforeseen issues which may arise at the higher RPM and TP values. There are many tables that are indexed by RPM and TP, and neither Calum or myself have the facilities to test every possible combination. The bottom line is that you and/or your favorite tuner will be responsible for utilizing this mod as you see fit.
All that being said, this is really exciting stuff, as Calum with the RTV2, and myself with TunerCode firmware bust some of the myths surrounding tuning with OEM Nissan ECUs. I can't wait to see how the Nissan wizards among you utilize the capabilities we're working on to your benefit. BTW, when you purchase a Calum RTV2, the TunerCode firmware (which includes this RPM mod, and much more) is included! Also, the TunerCode firmware is available separately and will work with any supported ECU (details soon), however you will need the RTV2 board to take advantage of the extra I/O capabilities it provides.