It's all about the proper training, and motorpacing can help a lot with speed. You need to do specific interval training to raise your anaerobic threshold and work on leg speed in a sprint. Practice 20 second spinouts in a 46 x 16, then 46 x 15. Then when you race in 46 x 14 you'll be able to hit a higher cadence, which translates to higher top speed. Also, what type of warmup are you doing before you race? You should first warm up in a lower gear, say 46 x 16, before switching to your race gear. Also, it's good to do some stretching before you race. Note that when I said close to 40 mph in a sprint, I didn't mean sustained for a full lap, but just the final 200m at most and upper 30's, not over 40. Remember that Power = Torque x RPM, so the faster you spin, the more power you produce, which translates into more speed.