[mrg666]

Originally Posted by CSG Mike

It depends on the impulse.

In the FA20's case, the E85 is easier, because the amount of **time** spent pushing the piston down during combustion is greater, rather than the amount of **force** against the piston. This is courtesy of the ignition timing advance, rather than exploding more gas with more air to get a bigger boom.

Another persoective: more timing advance allowed by ethanol allows you to harness more of the energy in the fuel used. You have the same energy density, because stoich hasn't changed, and your air intake hasnt changed. You are able to use more of it because you can advance timing without knocking. More boost = more fuel = bigger kaboom = more torque. However, because it's MORE boost, you (long story short) get LESS ignition timing, so while the boom is bigger, you are able to harness less of it.


Remember, engines don't deliver a constant level of torque like an electric motor, but rather, deliver pulses. These pulses are smoothed out by things like heavy pulleys, flywheels, clutches, transmissions, etc. E85 = longer pulse. More boost = stronger pulse. Net torque output = sum of the pulse, whether longer and/or stronger.


Hopefully that made sense. I can elaborate more. There's many other factors as well, but this is just a very surface level version.

I know new tune is necessary for E85. But I am wondering if JR factory tune can take advantage of higher than 93 octane fuel by advancing the timing?