Thanks Clive. No worries. I will keep larger injectors in my back pocket but for now I'm going to try to run without any further upgrades.
Had a long chat with my tuner yesterday to discuss the results in more detail to try and better understand my tune's characteristics and to also contemplate why I showed such a strong result.
According to him (and other tuners I have asked for confirmation) my injector duty is fine and the tune is safe. There should be enough fuel across the entire map for safety and there is definitely enough across the transition (hence the 95% peak injector duty) to protect from detonating in that area where most cars on twins usually let go that are badly tuned. I asked how much room I have to play with colder temps and he said basically on a 0C day (we mapped when it was about 11-13C) you may see an extra 2% injector duty at the very peak. Further, we discussed if there is enough fuel if I boost spike. The fuel cut is set to about 1.15 bar, or another 0.1-0.15 bar above my current settings and thus there should be more than enough fuel to withstand a spike to the fuel cut level if that were to ever accidentally occur.
The Apexi Power FC is very strict in how it operates. It cannot read fuel pressure and it cannot compensate for a lazy or failed injector. It reads the IATs, TPS, O2 sensor (if you have it plugged in), water temp and not much else to determine which part of the fuel and ignition timing tables to utilise (which your tuner will adjust). If your fuel or ignition system is not functioning correctly then the Power FC won't know about it and you may run into issues which may cause pre-ignition or detonation. It is a pretty primitive system.
As for why I made such good power? Well, besides a good tune by my mapper which looks pretty well optimised judging by the graph with only a few small improvements that could be made to smooth the torque curve further, we think it might be the following:
Knight Sports Twin Tube DownpipeThe Knight Sports downpipe has the following dimensions: 60mm (2.36") x 2 pipes feeding into an 80mm (3.15") collector to attach to the mid pipe. This means that the downpipe itself has an internal surface area of somewhere around 90mm (3.54") before the collector.
By contrast, the most popular downpipe for twins, the HKS, has an internal surface area of 75mm (2.95").
After discussion, we believe the larger downpipe has more benefit than initially thought because there is initially less restriction in the exhaust system. However, we cannot say for sure whether the twin tube design itself also has benefits over an equivalently sized single dump like the Australian made SMB 90mm (3.54") downpipe.
Water injection but not too much waterAs we know, water helps to keep intake temps cool so that the air entering the motor is more dense and you make more power since the ECU doesn't need to inject as much fuel and the combustion process is more efficient. However, there is evidence that too much water does have the effect of decreasing power by a couple percentage points and perhaps by running the smallest jet in the AEM kit I am running just enough to drop temps without having a small negative effect on hp. This might be good for a dyno run, but I won't know if I am injecting the right amount or too little until I do a track day next year and see how well it contains IATs and EGTs over a 15-20 minute period of abuse.
Anyway, that's our thoughts as to why the car was running so strong and surprised me a lot and surprised my tuner a little bit on the day. The larger downpipe and the right amount of water could be some differentiators. Or maybe, I have something else done to my car that none of us have noticed. Some secret engine builder sauce from Japan, even if my results are not necessarily out of the range of what's been evidenced by others around the globe with FDs over the past 20 years.
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