Was at a Thunderhill track day (HOD) yesterday. Filled up with 100 octane before the 3rd 30-minute session. In the middle of the 4th session I only had 3 bars and the car sputtered in a left turn (T9) like S2000s do when running low. I pulled off track and immediately started a slow ~45mph brake-cool-down drive to Willows (about 6 miles away) with 2 bars showing. All bars were gone after about a mile, and I ran out at the trailer park about a mile west of Walmart. There was no leaking fuel, and the car was running fine, it just gobbled the gas (there's normally >2 gallons left when the last bar disappears). Guy at the trailer park helped me get enough gas to make it to Chevron. Made it back to THill fine, and since I trailered there I don't know if the mileage is back to normal.

I only got ~100 track miles on the tank, and drove straight out the gates from the track without stopping. Could the 100 octane gas have caused my car to burn very rich when running hard on track, and that carried over to the slow street drive? I've never had even close to this high a fuel consumption on track before. I won't be able to drive the car again until a Reno Fernley track day in mid-October.

 

No, Higher Octane fuel will not cause your car to burn rich.
Something else has gone wrong...

 

Unless you're tuned for it, higher octane is not doing you any good.

fltsfshr

 

How much would the OEM ECU be able to tune itself with high octane fuel (= less knock) & high engine temps & high loads?

 

I hope it was unleaded.

 

Yes, road-legal unleaded. I haven't had a chance to look at it since Thunderhill, and I'll be at Reno-Fernley this weekend, so we'll see how how it does there.

 

you went from full to 3 bars after 1.5 sessions?

after a track day, i've gone from 2-3 bars to zero after just a few miles. Nothing strange. That's why I started bringing a gallon of gas to the track to put into my car at the end of a track day.

 

Yup, full to ~3 bars in 45 minutes on track. Then 3 bars to run out of gas (not 0 bars, but fuel-starved bone-empty tank) in 5 miles of 50mph steady driving. My fuel gage quickly jumps from 3 bars to no bars, but there's still plenty of gas in the tank (>50 miles worth) under normal conditions.

 

The tank gauge will sometimes read off when tracking - and the recovery to reading accurately may take some time and be abrupt.
This can also happen when you "overfill" the tank. I've filled up at a station with a steep right banking downhill and was able to get at least 2 more gallons than on a flat surface. The tank read 2 bars down for the first 20 miles, then abruptly went to full.
I'm thinking the track session caused your gauge to read higher than actual - and then suddenly read actual.

As for the consumption - I've heard of people getting as low as 6-7 mpg (average) during a hard track session in an S2000. I don't know what your average speed was during your 45 minute track session - but it sounds like your consumption would be a little more than that - perhaps closer to 5 mpg.

As for high octane fuel causing greater consumption - it will happen, but would be really no greater than 10-15% higher than normal. A stock S2000 (no ECU tuning) will see no advantage over ~96-97 AKI. Keeping that in mind, a lot of "100 Octane" fuel is not AKI - it's Research Octane. The equivalent AKI will be around 95-96 AKI, and therefore shouldn't cause excessive consumption.

 

If you got 100 hard track miles on a tank that is not out of line. In several years of track events I consistently got 8 mpg regardless of the type of fuel I used.