What is AKI?
What is RON?

 

AKI = Anti Knock Index
RON = Research Octane Rating

Google and Wikipedia are your friends

 

Got it. It would mean that fueling an IS350 with 87 (gas stations in the US use AKI index) meets the manufacturer's minimum requirement of 91 RON (IS350's manual). BTW, thanks for this insight, a subtlety I overlooked.

 

Im Sorry, but this post should be deleted!!! not sure why this question gets asked so often!!

if you drove a lamborghini or ferrari would you fill it up with cheap gas, pretty sure you wouldnt. So its the same for your lexus!!!

treat your car right!!!!!!!

 

Lambo is long way from Lexus. Lol.

 

i know that, but the motor still requires premium fuel! same topic different car

 

There is no such thing as cheap gas, all gas meets some minimum standard define and enforced through regulations. It just so happens that US/Canada uses a different rating that has been marketed by the oil company as "regular" and "premium".

Look at the actual ratings, the definitions behind them and what your car's manual says about what's needed for your car. The IS needs RON 91 which is equivalent to AKI 87. Would you feel better if the gas companies rebranded AKI 87 to Premium and then AKI 91 (RON 95) to Super premium? Not going to happen, they spent way too much in convincing people that their premium is better.

BTW, this doesn't apply to AKI 85 or some of the high ethanol content gas, that is equivalent to AKI 85 and then use ethanol to boost octane rating. Now that is cheap gas, but really not gas as it's simply alcohol with some gas.

 

In Florida, we have options of 87, 89 and then a jump to 93. Based on the ratings is 93 a bit overkill? 89 should be plenty good, right?

 

87 should be plenty good too. Federal Trade Commission and industry pundits insist there is absolutely no benefit (besides losing a few hp) of using higher octane fuel than the minimum recommended by your car's manual.

 

I realize this is 8 years late, but I can answer this.

The compression ratio you are describing is called Static Compression. Think of it as the engine not moving. What you’re asking about is Dynamic Compression (which is when the engine is rotating), and that can actually be much lower.

This is dictated mostly by camshaft lift and duration (how long/far the valves are open), and overlap duration (when both valves are open).

to give you an example, I put a giant Choppy drag race cam in my LS1 Camaro, and I was able to run 87 octane fuel because the dynamic compression was lower than stock. Could I have gotten more HP by tuning for more aggressive timing and using 93 octane? Absolutely. But I was a broke Engineering student, and saving that 10 bucks on a fill-up got me a chipotle burrito for dinner.

in short: compression isn’t everything - engine timing is.

 

Run 91 and nothing else, no discussion on this.

 

Yeah, this is an old thread, bumped for a reason that doesn't really answer the original question... closing.