Lag is indeed there on petrol on my current car, mostly evident on lift off from wot.
Also drove that BRC LPG 3.2 last week that I mentioned elsewhere, it has very slight lag on wot gear changes, but very slight and very gentle. The BRC has a feature that introduces injectors one at a time so any jolts or power increases when switching over are ironed out, seems to work in that it gets round the problem rather than solving it. Certainly not a jolt as experienced previously.
I'd be happy with lag at that level.
Vap is BRC's own branded and there some other little black boxes around the engine bay, plus extra vac references to the plenum. Injectors lead to what appears to be straws in the top of the plenum. :-?
So does the Stag 300. 
Kevin
Really? So was it working on my old car? There was a definate step in acceleration at wot if switching to petrol at say 4k, when the LPG button was pressed to switch LPG off. That wasn't present on the BRC system. :-/