Lost some oil

I attended training at the drag strip. Did some 5 runs I guess. Best time I could get at 1/8 mile was 10.915. I could write some 0.5 sec off because of shifting problems caused by destroyed synchros, but the car didn`t feel good. I think the ARC cooler gets too hot while waiting for the start.
Anyway. A bit of clutch smell and a bit noisier enginebay were the first negative parts, but then after 2 days I noticed that the engine had lost about 0.5 liters of oil. This is extreme, because after engine rebuild I have never seen any oil lost. Checked under enginebay and oil filter sandwitch, everything seems fine. The car didn`t smoke on drag strip either. Oil catch can is empty. I didn`t take the intercooler off to see what`s inside the turbo yet.
I filled up the oil and now after week driving it seems ok, no oil lost so far. I wouldn`t say that I drive gently in the streets, but not that harsh as on drag strip. Any ideas?