This is not possible to answer. On a different note, if you keep taking stimulants consistantly, you can fatique your adrenal glands and end up worse than you started. I appreciate that you want to increase your speed. It's all diet and training. Besides, you are only training 2 to 3 times per week? Hit some explosive weight training on your off days. Eat better etc. If you want pre work out supps then caffeine is not that bad, try arginine or any knid of nitric oxide booster. This dilates your blood vessels and allows more oxygen transport.
I am sorry it's not the answer you are looking for, but if anyone on the board recommends Winstrol (winny) to an 18 year old then you are getting bad advice. Many people on this board are current and ex-pro athletes. If you keep asking, you will get the answer you are looking for sooner or later from some with much less exerience. BUt my advice is to stay the hell away from Winstrol (winny) if you think it's a quick fix to a shorter sprint time.