Race gas?
 

So can the motor take or use anything higher then 93
octane and be ok with it? I tried searching didnt find any info.

I'd see no reason why it couldn't. Just don't use leaded gas. In some areas here in the bay they have 100 octane at the pump.

Why?

The engine is designed to run on premium pump gas. Putting in higher octane fuel will not produce more power, in fact it could produce less HP along with less fuel economy and worse emissions.

It's not the most accurate way to say it but think of Octane as a measurement of the fuels "resistance to ignite", or resistance to detonate.

If your car was designed to maximize the benefit of a fuel with high octane like race gas (over 98) then it wouldn't be able to run 91-93 octane, or maybe it could but with great struggle or great retardation in ignition timing.

Putting high octane fuel in your street car won't hurt anything other than your wallet. Just like having a car that is designed to run on regular won't be adversely affected by running premium, it won't be benefited either. The only thing that will be affected is the wallet.

It will run on Race Fuel, but you will likely see your mileage go down as the ECU isn't programmed to take advantage of the higher octane. Best stick to 93.

Why would mileage go down? That depends on properties of the fuel independent of octane...most driving happens in stochiometric closed loop mode.

Incomplete combustion would leave a surplus of oxygen in the exhaust indicating a lean condition which the ECU would compensate for with more fuel. Hence, lower mpg.

What incomplete combustion? Are you trying to imply that the race gas won't burn as well as normal pump gas?

If the greater resistance to ignite causes the "kaboom" of the combustion to be weaker or later in the phase of the stroke this can decrease power. I would imagine the real world decrease would be relatively negligible, however over the course of a full tank of gas and difference of 8-10 octane points then change could be noticeable or measurable.

The combination of ignition time+Octane rating creates the point of ignition and burn rate to maximize combustion power and efficiency. If you change the octane rating it is very similar to retarding the timing because the higher octane fuel won't ignite as readily and since the combustion chamber pressures aren't any higher to necessitate the higher octane, the ignite point and burn rate will be slightly decreased.

So yeah... What Draco said.

The whole point of race gas is that it's harder to ignite. So it won't burn as readily or as completely if the cylinder pressures aren't at optimal for the octane.

So in a normal engine, yes, race gas won't burn as well as normal gas.

I doubt that the rate at which 100 octane gas burns is significantly slower than the rate at which 93 octane gas burns. There is plenty of time, relatively speaking, for the fuel to "fully" burn in the cylinder, and I don't think there would be a problem with the oxygen sensor calibration if say E85 vehicles don't have a problem, and ethanol burns very slow. If the engine isn't set up to take advantage of the increased octane rating then you won't see an mpg increase, but I think it's crazy to say it'll go down. Even with variation across different fuels, the heat per unit equivalence oxygen is very similar for all hydrocarbons, even alcohols.

There's enough of a difference between 94 and 93 that you can no longer get 94 in most of the US since no cars could fully utilize it, leading to more pollution and lower mileage.

I'm not saying it's a drastic loss, but it might account for 1 or 2 lost mpg average across the tank. But the big issue the lack of any power gains to justify the large jump in price. Not sure about the OP's sources, but most race gas pumps I've seen are around $7/gal.

for street driving it is a waste of $$$....no doubt....

However if you are planning on an autox or especially a track day in high heat, its not a bad idea....

For example my old E92 M3 was a 12.0 CR engine that spun to 8400rpm & also required 93 octane..but in the republic of Kalifornia we only get 91...so when I took it to the track I filled it up with unleaded 100, just to be safe..... Some other M3 forum members did back to back dyno tests in hot weather and found the 100octane DID make more power, probably due to reduced knocks, and the engine running on its max timing map......vs detecting a knock and pulling timing....not much...around 10whp I recall on an engine putting down 360+whp

The M3 did have 8 knock sensors or 1 per cylinder...I don't know how many the FA20 has....prolly 4 since it is a newer design....and has higher static CR....

When I take my FR-S to the track it will have unleaded 100 in the tank...

DracoREX sure, maybe a tiny bit, but I don't even think the fuel consumption should be affected. 94 is pointless since cars don't ever "need" more than 93, blending the 94 down into more 93 is a good idea for the refineries, I don't think 94 and 93 are different enough to affect emissions though. "Octane rating" is something pretty vague and you can't really tie it to burn speed definitively. I don't know how 100 octane and 93 octane gas usually differ, but I would think that they're not different enough to cause a noticable change in performance on the same tune.

1 mpg on a 25-30 mpg car is less than the drop in fuel economy you see from 0% ethanol to 10% ethanol, and that's replacing gasoline with a much much lower (volume) energy density fuel.