sk429

Oct 94 gas is available here in BC Canada.

In theory 91 Oct and 94 Oct gas shouldn't make a differences because s2000
was made to run flawlessly without knocking with Oct 91 gas, should it?

My S runs OK when I use 91 gas. However, I feel slightly more HP, flywheel
seems to be much lighter and exhaust note is much quiet when I use 94 Oct gas.

Anything wrong with my s2000? If so, what should I take a look?

rob-2

You're getting high 'quality' gas as it's resistance to knock is reduced. However you will not see any power increases between 91 and 94.

Anything you feel, or experience is going to be in your head. As for extra HP measure it. Stop the stupidness with 'feel more hp'. If you cannot measure it, it's not difference. FYI even if you measure, it will be within the margin of error.

sk429

so there is no benefit from using 94 octane gas at all because 91 octane gas has sufficient resistance to knock? And drivers are not supposed to feel any differences?

There must be something differences, aren't they?

rob-2

octane rates are a resistance to knock only. The higher the oc rating the lower the energy level in the fuel as it's additives that reduce the chances of knock.

By your theory if you removed any chances of knock, ie the fuel you were running would never knock, you'd produce more power than stock. Which is simply not true.

Further more this car was designed to run on 91/93 oc. It runs best on that fuel.

If you can feel the difference between 91 and 94 fuels - you're in need of a mental exam.

askin

rob-2 is correct. Strictly speaking octane is the measure of the minimum temperature at which a mixture of gasoline and air will ignite and continue to burn. It has nothing to do with energy content. The 94 octane may have more cleaners in it but you shouldn't feel any difference.

Kirpich

^ Yep. BUT.

But for some funny reason his car, theoretically, could be just slightly more sensitive to knock, say a 'weak' knock sensor, and would run around on 91Oct without throwing a code, but the whole time pulling a few degrees of timing, especially at top RPMs, and mid-range? So when he puts that awesome 94 in, viola, all problems solved, and the 'weak' knock sensor, which used to react to that particular frequency, is at peace now.

Just a theory.

Or maybe that the 94 is considered high-end premium, and has none of that corn oil crap, the Ethanol?

INDYMAC

I think 91 octane is the minmum rating that should be used in the S2000 without causing engine damage. Is it the optimum rating for performance? Maybe for high altitude driving, but not lower elevations. I'm sure that some chart is in existence that guestimates optimum octane rating for high compression engines at a given elevation, but I don't have one.

In the Houston area it is not uncommon for fuel delivery traucks to dump leftover 87 octane gas into a 93 octane tank, rather than take it back to the terminal. The gas station owner pays the 87 price, and the customer never knows the difference. A win-win-lose situation IMO. But it happens.


For those of us that have owned our cars for awhile, we're pretty aware of when it runs well...even if it's a gut feeling and nothing else. If your gut tells you the 94 runs better than the 91, then go with your gut feelings.

SpitfireS

Since I bought the car I've used BP Ultimate 98, almost all of the time.
I remember using Shell V-Power (at the time 95 or 97, NOT 98) for 1 tank, I had to use something else because the filling station did not work, pumps damaged or something and I was close to empty.
So it was a full tank of V-Power.
Didn't notice much but it did seem to be slower between 6k and 9k rpm, at the time I thought I was "feeling things".
So I drove it with the Shell for a week or so, and then used the BP again - a full tank.
The first kilometer after filling up made me decide to never use anything but a proper 98 fuel again.
It was way better between 6k and 9k rpm, no doubt.


Btw.. what does the ECU do exactly to reduce knock, if it happens?
We're talking about true knock, detonation.
The only ECU controlled thing I found was:
Sure, you can change the engine design, load or rpm, but this the ECU can not do while driving

Chaning the timing is not in the list of things I found.

zeroptzero

All ecu's on modern vehicles should be altering timing when knock is detected . One test is to put a timing light on the crank while the engine is running and knock on the engine block lightly with a wooden handle, you should see the timing light make adjustments.

INDYMAC

This article does a nice job explaining how octane requirements can vary for each of us with the F20 (11.0:1) and F22 (11.1:1) engines based on where we live and drive...especially for Spitfire who lives below sealevel:

http://www.pinux-products.com/octane-rating/