One thing to note is that we use different octane rating systems on opposite sides of the Atlantic.
In Europe, they use Research Octane Number (RON), which gives a higher numerical result than Motor Octane Number (MON).
In America, we use AKI, which is the arithmetic average of RON and MON, calculated as AKI = 0.5 RON + 0.5 MON.
93 AKI American premium gasoline has equivalent knock resistance to 98 RON European gasoline, and has ever since we went to E10 as ethanol increases RON faster than MON.
Checking IAME’s manuals, all of their engines are designed for pump gasoline. The KA100, Mini Swift, X30 Shifter all require 98 RON. The X30 requires 95 RON (91 AKI), while no specific recommendation is given for the SSE 175. Vortex says that their Rok Shifter, Rok GP and VLR 100 use 95 RON fuel. TM specifies 98 RON fuel for their KZ engines. Rotax specifies 95 RON or 91 AKI for all FR125 engines; I have used 87 octane in a Max without visible detonation. While every currently popular kart engine runs on pump gas there are old modified motocross engines that have compression ratios higher than some diesels and really do require 100+ AKI fuel - if your track bans leaded gasoline, you may have to switch to methanol, which has its own issues but is 120 AKI.
Our fuel has as much ethanol and butane as the volatility and energy specifications can allow, as they are less expensive than petroleum-refined fuel components. Both of them are octane-rating enhancers and it has been at least a decade since I’ve seen a news story about a distributor or station being busted for selling fuel that didn’t meet the octane-rating specification. European pump gasoline doesn’t have as much butane or ethanol as neither of them save their oil companies money like they do here.
Now, can you just take out your 110-octane leaded fuel or 100/130LL avgas and pour in 93? !!!No!!!
Ethanol has a 9:1 air-to-fuel ratio, while butane and most ‘straight’ gasoline are around 14.7:1. You will need to enrich your fuel mixture because what was correct before is too lean now - by enough to cause a seizure if you used to be jetted correctly.
On my new X30, I switched from 110 leaded non-oxygenated fuel to 93, enriched the mixture, and re-tuned on track, then measured how far I moved the needle before getting it correct. It was 15 minutes (1/4 turn) more open on the low-speed jet and 10 minutes (1/6 turn) more open on the high-speed jet. On a Rotax the rule of thumb is 5 jet numbers on the mainjet (from 115 to 120) to compensate for pump gas.
If you are an American track owner and you’d like to get the lead out, go ahead - nothing is likely to go wrong. With this many kids hanging around the pit and driving in tight packs, and studies showing that any amount of lead is worse than no lead, getting rid of leaded fuel can help your image and perhaps benefit your drivers’ health and wallets.