few things here:
1.) Fuel system capacity - Going off the BMW b58, being that this engine is wildly similar, there are 3 "choke" points for the fuel system; high-pressure fuel pump, injectors, low pressure fuel pump. as of right now, I'm not sure anyone has been really able to test the stock fuel system. Maybe one of the people who put the hurricane in different cars using a standalone ecu. I don't have a jb4, so I'm not sure what it can log, but rail pressure, low pressure fuel and injector pulse width would be required to see which of the 3 items above are the weak point of the system. for direct injection turbo enignes, you'll usually see the rail pressure dip in the midrange first. since the hpfp flows more with more rpm, you'll often see the pump unable to keep up when you're at peak boost in the midrange. long story short, someone who has done testing will have to let us know what the system can truly flow.
2.) e85 - making your fuel mixture anything more than e20 without a tune is pointless. adding a little ethanol content will help help with the ecu pulling timing in hot weather or heavy load, but the only true gain would be cylinder cooling and that would be negligible. with a true flash tune, not just a piggyback, you can get some serious benefits from ethanol. You can increase boost, timing, tune the fuel correctly, etc. As long as the stock components are rated/capable of running ethanol, you can absolutely tune a stock engine/fuel system to run 85% ethanol. If the stock fuel system cannot flow enough e85 to support stock boost levels, a flash tune can just lower the boost so that not as much fuel as required, this is not possible with a piggyback. people will run e40, as staed above, because it is a good trade off where you don't need to lower boost due to lack of fuel, but you still get the majority of e85 benefit.
3.) jb4 and e85 - as stated previsuly, i do not have one and have never spoken to anyone there, but basically the jb4 takes your maf and map readings, changes them, then sends them to the ecu. basically, if your making 20 psi, it will take that reading and tell the computer its only making 19 psi, making the computer think it is not hitting its target and it will increase boost. same for airflow from the maf, it will tell the computer the engine is taking in more or less airflow depending on the desired outcome, leaner or richer afr's. when burger says the jb4 adjusts fuel, ignition, boost, etc; it is actually just the ecu making adjustments to false readings. just to clarify, this is not to say the jb4 is bad at all, it clearly has a great history and has been proven on multiple platofrms to work very well, i'm not sure i've ever heard of someone blowing an engine due to a jb4. here's where the e30 mix comes into play, they can only manipulate the sensor readings so much before you have safeties kick in, it becomes unsafe, or a sensor is maxed out. for example, a maf sensor can only output 5v, so without scaling the maf sensor table there's a maximum they can adjust how much fuel is added. I don't know that this is the case with e30 or if it is just the maximum flow of the fuel system, but piggybacks are limited in what they can do.
for those who don't care to read:
if they say a maximum of e30, keep it there
only way to know the fuel system limits is if we have a tuner capable of reaching them
