Quote:
Originally Posted by Ecky
No reason for higher octane fuel under normal conditions, no, since the ECU will only ever subtract (retard) timing, and never advance it.
Knock sensors are good to have especially on higher performance engines because they allow the manufacturer or tuner to tune advance at higher throttle much closer to the point of knock, since 1) you can't typically advance ignition enough on pump gas to get maximum economy and power at WOT, 2) under these conditions, knock can be very damaging to the engine, and 3) engine knock can vary based on conditions.
Just as an example, the TSX motor in my car calls for 91 octane. It has tables for ignition advance at 6 different cam angles which it interpolates, as well as tables which add or subtract timing from those other tables based on coolant temperature, intake air temperature, and other factors. But, they can't make a table for everything. What if the intake air sensor goes bad? Or, I get a bad batch of fuel? A knock sensor both allows them to be less conservative in their ignition tables and provides protection in case anything goes wrong.
It does, and what you suggest might work, but chances are good that part throttle ignition timing is already very close to perfect and more advance is not necessarily a good thing. Cooler air is more dense, and a higher density charge burns more quickly, so at part throttle it may actually pull timing for cold air, and it might add or subtract at WOT (or have tables for both) depending on whether the faster burn or higher cylinder pressures are more relevant.
I'll take a look at the factors I can modify on my Hondata ECU and get back to you.
|
Thank you for your help! That is a lot more complicated than I thought. I knew ignition timing was complicated, but I had no idea it is this complicated. If the ECU could be tuned, what kind of power/MPG gains could I possibly get by tuning it to run on 93 octane fuel? Maybe nothing if the timing is already ideal from the factory?
Also, since my ECU is from a JDM Honda Stream, is the timing likely to be any different than the stock US ECU because of Japan’s supposedly higher octane fuel?