89 octane on 91 setting with flashpaq???
JK Newbie
Joined: Dec 2007
Posts: 79
Likes: 0
From: Denver, CO.
If you run shy on the octane fuel you are running as compared to the octane setting of the programmer, you will start to run up against the knock sensors and retard your timing. If you are retarding the timing, you are taking away the benefits of running the higher octane tune. This isn't to say that it won't work, as the PCM will correct A/F mixtures but it won't work optimally.
My preference is to always run at the Tunes octane or higher. I don't want to droop any of the advance and I don't want the problems associated with running lean.
The half and half method works fine although it is a pain in the ass. Personally I would just aim high and forget about it.
Lastly, in my opinion and with the winter months, I always fall back to the lowest octane tune. I know because of how much longer it takes to get to operating temperatures I'm going to see a 10% hit in fuel mileage. Lower temperatures also reduce octane requirements and lower octane levels create more heat. That's why engines tend to knock more in the summer.
In round numbers, a 20 degree drop in intake air temperature reduces your octane requirements by 1. Of course the PCM takes care of most of this, but why would I dump a high octane, slow burning fuel in my tank when I can get a hotter/faster burning low octane fuel to go along with the cold dense air?
My preference is to always run at the Tunes octane or higher. I don't want to droop any of the advance and I don't want the problems associated with running lean.
The half and half method works fine although it is a pain in the ass. Personally I would just aim high and forget about it.
Lastly, in my opinion and with the winter months, I always fall back to the lowest octane tune. I know because of how much longer it takes to get to operating temperatures I'm going to see a 10% hit in fuel mileage. Lower temperatures also reduce octane requirements and lower octane levels create more heat. That's why engines tend to knock more in the summer.
In round numbers, a 20 degree drop in intake air temperature reduces your octane requirements by 1. Of course the PCM takes care of most of this, but why would I dump a high octane, slow burning fuel in my tank when I can get a hotter/faster burning low octane fuel to go along with the cold dense air?
That sounds reasonable. How about altitude? It stands to reason that with lower atmospheric pressure and the subsequent drop in compression, I should be able to run a lower octane fuel with a higher tune number without knocking. What are your thoughts on that?
JK Junkie
Joined: Jul 2008
Posts: 3,017
Likes: 0
From: Lakewood, OH
Yep, I agree. In round numbers you should be able to drop about 1 octane per 2500 feet.