1293cc A+ Series Turbo. High spec engine using SCCR box, SC drops, X-Pin diff, Omega Pistons, Steve Benross big valve head. Garrett T3 turbo. Omex 200 series ECU, Evans Waterless Coolant, 74°C thermostat, etc, etc, etc. A proper engine. Not some cobbled together ebay second hand engine.
Water temp is constantly good, sits at 65°C at normal driving, gets to about 85°C when driven hard on a hot day. Oil pressure sits at about 70 PSi when driven hard, 30-35 PSi at idle when hot.
Above engine has a weird an unexplained misfire.
The background:
Car on the dyno would produce good power and good torque (150bhp. 150 lbs/ft.)
Engine would drop to 3 cylinders on high boost and high load (13 PSI. 4th Gear)
Using the car on the road, the problem persisted.
After doing some research, I ditched the waterless coolant I was using and went back to using normal 50/50 mix of anti-freeze and water.
Using the car on the road again, misfire on high boost, high load = Gone. Excellent!
BUT! Using the car on a race circuit after about 2-3 laps on full chat (so high load. high boost) misfire reappears.
Initially I thought it could be fuel starvation. So brimmed the full tank and went back out, same thing happens after about 2-3 laps. So I do not think it can be fuel starvation. When getting back in the car on the road I can drive it "hard" and the misfire does not happen.
When it begins the misfire, the car pops from the exhaust, I usually get a "pop" sound out of the air filter (could possibly be the dump valve) and then it just vibrates, looses power (but not total loss of power, it will still accelerate but not very quickly). It's hard to hear it every time, but I occasionally get a mechanical "ticking" noise at the same time (sounds like a tappet-type noise?). The misfire gets worse with the more laps I do.
If I put my foot on the clutch and let the revs drop to about 1,000 rpm (so it's off boost and no load) for about 4/5 seconds, and release the clutch, the engine runs as normal and I can continue driving, even when doing 70/80 mph.
My head is telling me it must be something to do with the extra heat generated when using the car at full chat for an extended period of time (i.e on the circuit). Apart from this, I have no idea what it could be?! I don't want to go changing a heap of parts/things to no avail.
Any advice would be greatly appreciated. Thank you.