This question seems to pop up every couple months. For $6.99/gal, you're wasting your money big time.

 

you'll have 250HP STOCK!! that's why in japan's s2000 spec is 250HP, because they use 100 Octane in japan. in US for 93 octane you can only get 240HP out of it.

 

Your logic is a bit flawed. The JDM s2k produces 250hp because it has a higher compression ratio than USDM/EUDM -- which is possible because Japan has higher octane fuel readily available at gas stations.

Rephrase: "The power isn't produced by the fuel itself. Its because of the higher octane fuel available that a higher compression ratio can be run."

 

This is certainly part of it.

However, the octane rating system is different in Japan, Europe and much of the rest of the world.
http://en.wikipedia.org/wiki/Research_octane_number
Japan uses the RON (Research Octane Number) system of measurement. The U.S. uses the (R+M)/2 method for octane rating, which is a more accurate measure of octane (follow the link if you want to know the details).
In reality, 100 octane in Japan (RON) is the equivalent of 95 octane in the U.S.. Additionally, the HP measurement system is not the same either.

babys2k: you missed the message.
The facts are in the science. Read my previous post, follow the links - and then maybe try again after you understand it a little better.

 

This is certainly a valid argument.
If you can find 93 (AKI) octane, I believe it's worth it. More for the little bit of peace of mind a 93 (AKI) octane number may provide you concerning detonation, than anything else.
However, race gas really won't do anything for your car unless it's force fed.

It's more important you use a quality gas (Chevron, Shell, Amoco, BP) than use a gas with an octane rating over 91 (AKI).
Using a high quality fuel treatment (like Redline's SI-1) is also very important.

 

Well...from driving through a lot of states from Ohio and moving into Arizona..I was surprised to see the differences in octanes. Mainly east coast is 93, but then driving into Texas it was 90 for premium, and into NM and AZ the highest was 91. You can get 100 octance but the cost of 7 bucks a gallon though. So depends on the area you live and the climate I guess will dicate the octane rating.

 

250ps =~ 246hp

 

One last point is that any fuel listed as "race gas" at the pump is not regulated and typically is rated using the RON method. Many of the fuels listed as "racing fuel" or gas do not have any detergent additives - and this is not good.
In other words, you may be getting a crappy 95 octane gas at best.
Check the pump and/or contact the fuel supplier to determine the method which the fuel's octane rating was determined, and whether or not the fuel is blended with detergents. And once again, do not run a leaded fuel in your S2000 (regardless if you

 

Let me put some prospective on the subject...

If you want better performance from your gasoline, only fill 1/2 tank at the pump. The weight reduction of ~6 gallons of gasoline will be more significant than the difference you'd see between 91 and whatever else you might run.

 

I've posted this before. Using 100 octane and resetting the ECU I was able to draw 16 additional horsepower from the stock engine over the 91 octane.

The factory ECU pulls timing when it senses the slightest ping. Running higher octane will eliminate the ping that pulls timing and you get the full advantage of the timing for this engine.