Standard plug can last up to 20k -25k kms.. Reccomended to be change every 2 service intervals.. Mean while for iridiums it can last up to 100k kms.. (based on my understanding)

U can google up for better understanding about these plugs...

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Added on December 25, 2011, 8:51 pm
For me what i can see that we install nvg.. We will loose the trunk space..since the trunk is already small..if u wanna install it under the car i guess its impossible...

For me.. Empty tank weights around 45-60kgs (depends on material).. Put more burden on car.. Abs cepat kong.. Tire ware cepat kong..  (i am very particular about weight...) ( ehem.. Camel u know what i mean...) hahaha..

Thats what i see.. Since its a small car i find it not that pratical for me.. Since the fc is already good.. (seems pretty well for me as i can clock 450-500 with a full tank..moderate mixed driving)

But its not wrong to install to your viva.. If u are willing to loose ur trunk space..

sifooo 

anyway bro davinyan,

if Fuel Consumption is your top priority, viva manual is the best choice in the market (manual savvy too ).

i would suggest to go for the 850cc. 660cc will be too underpower. 1L on the other hand, will give you the power and consume a LITTLE BIT more fuel than 850cc. this however depends on your right foot, if you're light on your throttle pedal, 1L might be as fuel saving as 850cc or even better due to the engine might need a little less effort to move the car compared to 850cc.

NGV, apart from the space problem as been highlighted by bro Ilyas, there is nothing wrong with it.

But, if you take a long term calculation onto the table, i will say that the cost of buying a 850cc manual viva+installing NGV+daily fuel and NGV refill+car maintenance will not be much cheaper than buying the 850cc manual viva+daily fuel+car maintenance.

it might save you just A LITTLE BIT due to the fact that viva is already a fuel saving car. so, ask yourself, are you willing to lose the boot space just for that a little bit of saving? i can't, as my boot space is always full with my helmet,glove for my racing activities and of course when i go out with GF, we need that space to put stuffs in after shopping