You should not consider LPG for a performance car. There are too many disadvantages and nonsense as well. First of all LPG aka propan butan bottles are very heavy (methanol even heavier) that all the weight you lost from stripping the car is put back on. Second I wouldn't advice going for 50 liter bottle to save on weight because I can only manage 100km and had to switch to benzin to go home. 100 liter is a must. The main reasons why you don't want the converstion is because if you car does 9l/100km the consumption goes to 13l/100km. Corbs whoever said or estimated 10% power loss is a bit short on truth. I won't give it 50% but I'd say............maybe 35% but it's vehicle dependent. Turbo? Put 50% for me then. You will probably save more money by detuning the turbo or removing it completely from your SR20's.
This is my opinion at least. I drove a Golf Mk2, Audi 80, Passat Mk3-4, Lada all on LPG and although I liked it, those cars were run around which is the whole point of LPG. I don't use it anymore and now I drive on Methanol which is a bit dangerous as it doesn't smell and you don't know when your bottle is leaking. Don't worry this stuff is not available in UK. The device is different too. Oh yeah, last summer I managed 130km/h top speed in a 1.6 Golf Mk2 so that kinda speak for itself. And one more important thing to consider. You probably going to suggest 'what if I get the auto switch type, so I can change instantly inside the cabin?'. Well as BOLF already mentioned car must be tuned via ECU, so switching back to benzin some times can cause missfire, but even if it's running smooth the ECU is already mapped to run on LPG and performance is gone down the drain.
p.s Niko if you going to ask me again where I got my facts from, I use this site so check it out:
Yahoo! Answers - Home