I understand that the ecu contains high and low octane fuel maps as well as high and low octane timing maps - and that the ecu automatically chooses which maps to use based on the octane of the fuel.

Meth/alky injection is basically just a method of increasing the effective octane of the fuel. Obviously the high octane maps on a meth injected car would be tuned with that higher octane in mind.

So couldn't the low octane maps be tuned to compensate for a meth injection failure? Why isn't that an effective (engine saving!) failsafe? Is it because the ecu reacts too slowly in switching the maps? Or is it that even the most conservative possible low octane map still isn't enough to compensate for the high boost conditions?

By the way - I realize there are very good failsafe kits on the market today for meth/alky injection kits, and I certainly wouldn't run without one. I'm just asking to try and understand how the low octane map is typically used on a meth injected car.

 

Depending on the system you use really depends on how you tune. I am using the Snow Performance kit. My failsafe is the solenoid that will cut boost to wastegate which is 12-14psi. I will not even touch the low map because the if the ECU switches to the low map I will not be spraying. I am only tuning the hi map for fuel and timing. Some one please chime in on this.

 

u could make the low octane map overly rich...... im thinking u could figure out how much load your car pulls on 12-14 psi and tune that part of your high map rich but im not 100% sure on that just saw that on a couple peoples maps

 

Short answer is no. The ecu does not "switch" to the lowe octane map, it decays to the low octane map as the octane number decays to zero, by the time you hit 0 and are fully using the values from the low octane map you probably would have had to throw hundreds of knock counts over several minutes and even then it would drift back to the high octane map as soon as the knock subsided.

In short, if your meth tune is agressive, your motor would probably have already let go before you were on the low octane map.

 

Its just not a safe way to tune.. Since the Octane number is a trim, it is what determined which of the maps it uses, but it interpolates in between.

Although one large knock incident can be enough to instantly switch the maps, it would already be too late to save you from damage if the tune was aggressive enough.

This is why we use failsafe products, so if anything does something unexpected, it instantly cuts boost before it can get high enough to cause a problem (with meth pumps and controllers that fail on occasion)

Now, with that said, if you get off it as soon as you see something wrong, the odds of doing damage aren't very high when your dealing with typical pump tunes, But with an alky tune, you would run lean and have aggressive timing, you can still do damage pretty quickly if you push it, especially over time.