Race Fuel (approx 105 RON)......safe? Make a difference?

[Northnoble]

Daft question for those that are a lot more technical than me.

Last race outing I was offered some "race fuel" by a mate who basically wanted to empty his Jerry can before heading home. Not sure of the exact spec etc but he said it was circa 105 Ron.

Would it have been safe to pit in the Atom and would it have made a difference to performance?

Just curious

[Lord Studley]

If it's good enough for the space shuttle............ Lol.

[phil4]

I expect it'd have been safe, but just as putting 98 in a car tuned for 95 (ie. most normal performance cars) wouldn't do very much at all, I'd doubt 105 would have much benefit to a 98 tuned car like the atom.

[Steve Gibson]

The higher the RON, the more resistant the fuel/air mix is to pre-ignition under compression (i.e. when your piston is rising).

With a higher RON, you're making that pre-ignition (knocking) even less likely. I used to run a supercharged MX-5 back in the 90s and it had a little aftermarket sensor fitted to detect knock. On very hot days, on 95 RON, you could tell when the sensor was retarding the timing to stop the knocking. It felt noticeably less powerful. On wet, cool days it flew along. Ironic really. The ideal conditions for the engine were the most dangerous for the driver.

Nice bit on Wikipaedia here:

In the case of the normally aspirated engine, at the start of the compression stroke the cylinder air/fuel volume is very high, this translates into a low starting pressure. As the piston travels upward, abnormally high cylinder pressures may result in the mixture auto-igniting or detonating, which is why conservative compression ratios are used in consumer vehicles. In a forced induction engine where at the start of the compression stroke the cylinder pressure is already raised (having a greater volume of air/fuel) Exp. 202kPa (29.4Psi) the starting pressure or air/fuel volume would be two times that of the normally aspirated engine. This would translate into an effective compression ratio of 20:1 vs 10:1 for the normally aspirated. This is why many forced induction engines have compression ratios in the 8:1 range.

Many high-performance engines are designed to operate with a high maximum compression, and thus demand fuels of higher octane. A common misconception is that power output or fuel efficiency can be improved by burning fuel of higher octane than that specified by the engine manufacturer. The power output of an engine depends in part on the energy density of the fuel being burnt. Fuels of different octane ratings may have similar densities, but because switching to a higher octane fuel does not add more hydrocarbon content or oxygen, the engine cannot develop more power.

[GTED]

Race gas or gas with higher octane would only increase performance of the car, if the ECU has a properly matched tune, i.e., timing and a/f ratio.  Otherwise, higher octane gas actually is a slower burning fuel, without a proper tune for it, you might actually lose some acceleration...  One time at a top speed shootout event with friends, I had a tank full of race gas (not with my Atom) and on my handheld device, I accidentally selected the regular tune instead of the race tune.....  All the friends with the same car and same/similar set-up as my car reached/broke their target Speed, but I was 2-5 mph slower.  I didn't realize I selected the wrong tune until on my way home, after filling up with pumped-gas, I was going to switch back to the regular tune...., that's when I realize I was running that tune during the event...

GTED