ON ROADCIRCUIT ASSOC.

ORCA rules (aligned with EFRA) mandate 16% EU-spec nitro — no exceptions, no imported higher-% fuel. Using 20% or 25% fuel gets you excluded on the spot at scrutineering. At 16% a medium plug (OS #6, Novarossi R4) is your standard choice. Go hotter (OS #8) on cold damp Irish mornings when the engine struggles to stay lit. Always use fresh fuel from a sealed container — opened fuel absorbs moisture, causes inconsistent mixture, and can score a piston by running lean without warning.

A failing glow plug is responsible for more DNFs at club level than anything else — and it's almost entirely preventable. Check the filament before every qualifying heat: touch your glow starter to the plug header and look for a bright orange glow. Dull red or no glow = it's failing, replace it now. Don't wait for it to die mid-final. Carry at least 3 spares in your pit box. Change proactively every 2–3 race days regardless of how it looks. OS #6 is the club standard at 16% nitro; Novarossi R4/Medium are also popular with Irish GT runners.

At 16% nitro your car should trail a faint blue-grey wisp of smoke at full throttle. White billowing smoke = rich (safe but slow). No smoke at all = dangerously lean and engine damage is imminent — richen immediately. Always tune in one-click increments. The HSN (high-speed needle) controls full-throttle mixture. The LSN controls idle and corner exit — if the engine stutters or dies coming off corners, richen the LSN a half-turn. In cold, wet conditions at St Anne's: richen both needles slightly. Cold dense air holds more oxygen per volume and your engine will lean out compared to a warm dry day without any needle changes.

1/8 GT cars don't have a centre diff — they use a 2-speed gearbox instead. You only have two diffs to tune. The front diff runs extremely thick oil — typically 500,000cst up to 1,000,000cst (i.e. effectively locked). This keeps the front end planted and stable under power on smooth asphalt. A thinner front diff will make the car feel darty and unpredictable. The rear diff is where the real tuning happens: 30,000–50,000cst is the normal working range. Thicker rear = more straight-line traction and stability. Thinner rear = more steering, especially on entry. Start at 30k rear and build up if the car feels loose on power. Never change both diffs at the same time.

ORCA rules permit tyre additives — use them. Apply 20–30 minutes before your heat and store treated tyres in a zip-lock bag to retain the effect. Medium compound is your dry St Anne's starting point. In wet conditions softer compound is not optional — hard rubber on a wet track is a skating rink within 2 laps. EFRA's 2025 GT European Championship confirmed the softer PMT Q3 compound outperformed harder choices in variable conditions. The rule almost everyone breaks: never rotate tyres front-to-rear — it fundamentally unbalances the car. Mark each tyre FL/FR/RL/RR and keep them on the same corner all day. Pre-glue inserts the night before; cold CA glue in an Irish morning doesn't fully cure.

1. Drain the fuel tank completely — old fuel left in causes carburettor varnish. 2. Run the engine lean until it stops — burns residual fuel from the carb throat. 3. Clean the air filter with dedicated filter oil — a clogged INS box starves the engine and is illegal under ORCA rules (INS box mandatory). 4. Squirt after-run oil into the carb inlet and turn the engine over by hand several times to coat the bore. 5. Check all ball studs — grab each suspension link and try to wiggle it; any play = replace the ball stud. 6. Check brake pad wear and glow plug condition. 7. Gently pull the tyre bead from the rim on each corner — a loose tyre discovered in the pits is far better than one departing at 60+ km/h on the straight.

ORCA runs 3×4 minute qualifying heats on a stagger start (Rule 6.4) — you're racing the clock, not the car in front. Let faster cars through immediately or risk a Stop-Go penalty. In qualifying: consistent clean laps beat one fast lap with a spin every time. For finals (20–30 minutes): at 125ml max tank capacity you need 1 pit stop in a 20-minute final, 2 stops in a 30-minute. Practice your stop — target under 25 seconds (fuel, plug check, bodyshell clip). Each extra 20 seconds in the pits costs you approximately one lap at club racing pace. The top 3 cars face scrutineering immediately after the final (Rule 4) — do not touch your car until the scrutineer releases it. Corner cutting (all 4 wheels off track, Rule 8.4) earns a penalty even if you rejoin without advantage.

Under ORCA rules (Rule 6.10) a wet race is decided by drivers' vote and opens up a second car option (non-shareable). Wet setup changes that actually work: richen both needles 1–2 clicks (cold dense air needs more fuel), switch to softer tyre compound without debate, reduce front wing angle to reduce aquaplaning drag, raise rear ride height 2–3mm for puddle clearance, go 5–10wt softer on shock oil front and rear for more mechanical traction when rubber grip disappears. Key St Anne's note: the concrete pit exit apron turns to ice in the rain — exit the lane at walking pace or you'll be the day's entertainment before you even reach the track.

The scrutineer can inspect your car after any heat and will definitely check the top 3 after the final. ORCA specs to know by heart: minimum weight 2,350g (ready to race, tank empty), max engine 3.5cc, max carburettor bore 9mm, max fuel tank 125ml, 16% nitro only, INS air filter box mandatory, EFRA-approved exhaust only, EFRA-approved body or within EFRA measurements. Gurney flap permitted — max 5mm above the rear body line. Electronic driver aids are absolutely prohibited. Rule 6 also requires that your car number is correctly displayed (Rule 7.3) — a car with the wrong number won't be permitted to start. If you have any doubt about a part, ask the Race Director before the race, not after the result.