Mixing

Can I mix, let’s say e85 with 93 octane to help with some extra power? If so what would I have to do to find my final octane mixture and my afr? Or would it be a better choice to just install a flex fuel system to do all the work for me? Thank you in advance.

You can tune for any fuel and optimize the power for that fuel. Whether it will make anymore power than strictly 93 octane not necessarily a given. If your engine can benefit from E85 (i.e. make more power, run cooler, etc), then it's usually best of you can run a flex fuel system so you can run 93 if E85 isn't available.

E85 on its own doesn't add power. This is a common misconception.

It enables you to do things in your tune, you might otherwise be limited by due to petrol's nature

What E85 enables is a more controllable combustion as its a less volatile fuel, eg it will likely only go bang when told to vs petrol which is far more volatile and can go bang unexpectedly, this is what we refer to as knock or pre-ignition where the cyclinder conditions means that the petrol will combust before the spark plug fires.

Some of the things that can increase the likelihood of pre-ignition is too much timing advance, too much cylinder temp, and cylinder pressure

So if your fuel is more stable, you can add more ignition timing advance as its far more predictable when the bang will occur, and that it will occur when the ecu commands, not before (knock) which can mean the piston may still be traveling up when it goes boom, this is a great way to eject poor rodney out the block.

And because E85 is less energy dense than petrol, you need more of it, lots more to produce the same amount of energy in the combustion (power), this need for more fuel is why E85 has a cooling effect. Its basically like using a spray bottle on a hot day, it helps cool the combustion chamber simply because of the amount of liquid being injected.

Also worth noting, adding too much E85 to a petrol tank without accounting for it in the tune is potentially dangerous as you could lean out the engine. This is why flex fuel sensors exist. They allow the ECU to add more fuel to ensure the correct AFR's are still hit based on the amount of ethanol in the fuel.

Thank you guys this helps me understand better what I’m doing and what I need to do to help my engine run more efficiently. I am planning on using the Cobb flex fuel kit. Anyone here using this currently that could give me some pointers?

Almost every modern vehicle is made to accept a degree of ethanol in the fuel, some quite high levels - but older vehicles may have plastics and, especially, rubber/flexible hoses that break down when exposed to fuels containing ethanol.

I'd suggest you check carefully. I don't think it applies to you, but some vehicles, for different markets will, or will not, be OK for these fuels. I know my vehicle is fine acording to the manufacturer (checked several reliable sources, including the manufacturer), being "NZ new" spec', but the equivalent JDM imports are not.

Andrew,

The flex kit is the way to go. I'm very familiar with the COBB flex fuel kit if you run into trouble, but COBB has great customer support as well.