Originally Posted by
vertigo
Improperly calibrated injector parameters? That is a pretty elegant way to put it :] If we are talking about stock ECU cars, no nissan ecu has been completely reverse engineered to the best of my knowledge, so I highly doubt all of the fuel routines have been calibrated correctly. The larger u drift from stock injectors, the more these issues become apparent. And short of using an injector flow x duration look up table, the curve is going to be different than stock. Sure you can get it somewhat close with tuning, but its all black magic because the people who are tuning cars, are not using the right equipment, and typically dont know enough about engine dynamics to properly tune a car. Their idea of tuning, is getting a certain a/f ratio on a dyno @ WOT. That is why there are so many shitty running cars driving around.
but all of this is irrelevant, you cant deny that 550's are more desireable from a tuning and streetability standpoint. Nothing about waldo's setup says he will be making more than 350whp from what i have seen. Plus if he does go for serious power later, injectors are easy to swap. There is a reason OEM's more often than not, put in JUST enough injector to support max power.
Certainly, for a setup that's 350whp and is flow limited to that, I'd rather see 550's and 4-bar fuel pressure than 740's for a street car. That's not always the rule I use, though. I've found more often that not, that OEM's (Nissan at least) size the injectors to match the max flow of the turbo. That way, if for some reason, there's an issue with the wastegate, the ECU can at least fuel the motor properly, engine strength not withstanding.
The issue with going way bigger than stock on a retuned stock ECU is that you have to know where all the corrections are. Ignore these and the bigger the injector, the more you're off.
About reverse engineering, Hi, I reverse engineered the S13SR ECU injector settings in the source code. The stock ECU mainly injects fuel based on MAF sensor flow, plus fuel map corrections, plus short and long term fuel trim. Everyone knows that part. On top of that, there are 2 settings for injector lag time: a lag scalar and a voltage compensation. Additionally, there is a minimum injection time setting that most tuners trip over. That's it, apart from the numerous warmup fueling routines. Basically how a standalone does it. Not trying to be a dick about this at all, but we're not still stuck in 2002 on the ROM tuning front.