i thought there was a few VLs around to runing very low times on LPG (and if not im damn sure there are some V8's), but on fullboost its sayin that the RED XE(F?) is the first running 9s on LPG.
as for the backfiring, good systems hsouldnt do it. i was reading up on one the other day, an XR6T makin about 368rwkw (automatically switching between petrol and LPG as the injectors oculdnt supply enough LPG high in the rev range) and supposedly the guy started it and straight away gave it a good hard rev... no backfire, and if he did it that time, it would only have been because he knew it wouldnt backfire... so in short, wait for a bit more developement before going LPG. i thought LPG was at 110 too, but now that i know it isnt, its not lookin as appealing