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Since I took delivery of my F, she has been drinking 93 octane. I just realized I can get 94 octane from Sunoco locally without going out of my way. Seems like a no brainer to switch to 94. I have a few questions.
1) The gas cap sticker just says “Premium unleaded fuel only”. What will 94 do compared to 93/91? Increased performance? Any horsepower gains? Increased engine longevity over the long term?
2) I have 3/4 of 93 in the gas tank right now. Do I go near empty before filling her up with 94?
3) After the first 94 fill up, will I notice or feel anything different on my first spirited driving with 94?
Yes, you should notice a slight difference. Octane 93 and Octane 94 difference is very small so you won't notice as much of a difference as you would if you jump from Octane 91 to Octane 94. I only put Octane 94 in the RCF. I have tried Octane 91 as well and there is a very noticeable difference.
To answer your questions:
1) Premium unleaded is a bit subjective. In North America, we call Octane 91 premium unleaded, but Octane 91 is the bare minimum at best. People in California are stuck with Octane 91 and cannot get any higher than that. I use Octane 94 on my RCF 100% of the time and Octane 93 on my IS350 F-Sport. I have read very high compression cars like the RCF (12.5:1) are actually tuned to deliver full power at Octane 93 or higher. I have heard RON Octane 100 (that translates to Octane 95 in North America) is what is considered premium high Octane in Japan. I firmly believe RCF cuts timing on Octane 91 fuel, which why I feel a very noticeable difference between Octane 91 and Octane 94. In short, the car is not gaining any power at Octane 94. It is just that Octane 91 is below what RCF was tuned to deliver full power at.
2) No. Does not matter. You can mix and match fuel Octane levels as much as you want as long as you are above the minimum required.
3) Yes, a small difference going from Octane 93 to Octane 94. Ir could be a bit of placebo effect since it is a very small increment. Octane 91 to Octane 94 is a very noticeable difference.
What would be the maximum octane the RCF could handle in theory? I have read that you can mix different octanes to achieve a higher desired octane. This is probably overkill for street driving anyway but leads to a good discussion
What would be the maximum octane the RCF could handle in theory? I have read that you can mix different octanes to achieve a higher desired octane. This is probably overkill for street driving anyway but leads to a good discussion
RON Octane is not a type of Octane. It is an Octane rating system. Outside of North America, there are two Octane rating systems RON and MON globally. North America uses an average of RON + MON/2. So, Octane 100 in RON system used in Japan, is equivalent to Octane 95 in North America.
Regarding what is maximum RCF can handle, race gas is around 100 Octane in North American rating. I would not go higher than Octane 100.
Have you guys tried running a full tank of 100 octane?
So from my understanding, with Cali's 91 octane I'm not getting the full 472 HP then?
Yeah, I strongly doubt you are getting the full 472 HP from the watery cr*p they sell in California. You can always try dyno'ing your RCF and see what the numbers look like. They should be around 400 - 410 whp SAE corrected stock. Weaker numbers are around 380 - 390 whp when the car is not making full power.
Last edited by 05RollaXRS; Nov 7, 2023 at 11:31 AM.
Let us know if your MPG is affected, as well. The stock ECU may just compensate for any additional (or lesser) amount of octane and you won't even notice a difference.
I'm in Arizona with crappy California 91 octane fuel. My KCLV on my LC was a constant 18 or 19, I could never break 20. For the past two years I have been using Lucas Octane Booster. My KCLV now runs between 22 and 24. And, yes, I can feel the difference. The stuff really works:
I'm in Arizona with crappy California 91 octane fuel. My KCLV on my LC was a constant 18 or 19, I could never break 20. For the past two years I have been using Lucas Octane Booster. My KCLV now runs between 22 and 24. And, yes, I can feel the difference. The stuff really works:
i can confirm Lucas Octane booster. On straight 91 the car feels like the ECU is pulling timing or correcting for the ***** gas we get. Every time I put in an octane booster she wakes up…I thought it was placebo until I read a few people here and on the ISF forums confirm better KCLV readings.
i really hate Cali sometimes but the Mexican food is outstanding…😂.
Does Octane Booster cause long term harm? I have heard it results in injectors getting clogged or something like that. I have used Octane 94 + STP Octane Booster a few times and then car is literally trying to get away from you. There is definitely some difference there with Octane Booster.
Does Octane Booster cause long term harm? I have heard it results in injectors getting clogged or something like that. I have used Octane 94 + STP Octane Booster a few times and then car is literally trying to get away from you. There is definitely some difference there with Octane Booster.
No, quite the opposite. In fact, fuel system cleaner is mostly higher octane gas along with some additives.
Filled her up with 94, only needed 1/2 tank. I let her loose leaving the gas station and the engine sputtered a bit switching gears, not sure why but after that it has felt fine. Like Rolla said I haven’t felt a noticeable difference yet.
Haven’t tested mpg, but I did reset the mpg after the fill.
94 Octane
