l have an Alto of 2004 make in Delhi...Due to the high cost of fuel l am thinking of fitting a CNG or LPG kit...

1. What are the pluses and minuses...

2. What about warranty of the vehicle...???

3. What would be the cost per km as compared to petrol..???

4. Would the maintenance be high..???

Please advice...

l had a service truck that we could run on either gas or LPG. When running on LPG, it would start much quicker in the winter. The truck seemed to perform less while on LPG. The tanks did not seem to last too long either. As for maintenance, there was not any that l was aware of. The trucks were sent out & converted. l believe that there r kits available to convert a lot of cars over. We had a toggle switch, when we wanted to choose fuel. After the novelty wore off, we pretty much just ran them on gas. We got tired of replacing the two LPG cylinders that were in the back of the truck.

Cost of LPG / CNG is less, but mileage is definitely less, so unless u travel around 100 KM per hour, it may not be worth the 30K u will be spending on the conversion.
The installation has to be done by experienced & authorised people, & has to be well maintained, else the thing can get dangerous.
Your is is a 2004 model vehicle whose warranty has expired. So why worry about it?
THe car has to be retuned, so when tuned for LPG/CNG, performance in Petrol is going to be very bad; & when u tune for petrol, performance on gas is going to be bad. A compromise, of course, means that performance on both fuels is bad.
Vehicle sound will change after a few thousand KMs when u run on gas.
CNG is available only in metros & select cities, unlike LPG. Even LPG is available in very select pumps. So u will be in a difficult situation if gas runs out.
When l got a new WagonR, l explicitly decided against the LPG version for just 1 reason - safety. LPG is highly inflammable. If CNG is available in ur area, go for it, but remember that u will have to use petrol on long drives.
l do not think maintenance expenses will be very different.