Then don’t time lap to lap, time the whole session and then divide by the number of laps.
There is no AMB loop decoder there. The best idea, as already posted by Nick, would be the Hot Lap system;
That is, unless you want to spend the $10,000 for all the neccessary equiment and software, clicking on the “ebay Motor” link is kinda useless 
Base System
TranX2 EL Decoder with cabling $7109.00
Loop set for tracks up to 20m (65 ft) includes coax and connectors $630.00
Software
Orbits 3 Race Timing Software $2275.00